Eye tracking device

Abstract

In one example there is provided a device for tracking movement of an eye. the device comprises: one or more light sources for illuminating the eye; a first cylindrical lens and a first linear camera for imaging the eye, wherein the first cylindrical lens and the first linear camera are positioned so that the first linear camera images the eye through the first cylindrical lens, the first cylindrical lens being oriented substantially parallel to the first linear camera; and a second cylindrical lens and a second linear camera for imaging the eye, wherein the second cylindrical lens and the second linear camera are positioned so that the second linear camera images the eye through the second cylindrical lens, the second cylindrical lens being oriented substantially parallel to the second linear camera, wherein the first cylindrical lens and the first linear camera are oriented substantially non-parallel to the second cylindrical lens and the second linear camera.

Description

[0001] EYE TRACKING DEVICE

[0002] 1. FIELD OF THE TECHNOLOGY

[0003] The field of the technology relates to devices, systems and methods for tracking movement of the eye. In particular, but not exclusively, the field relates to eye tracking devices for obtaining information on eye tracking for use in assessing medical conditions, for example in the ability of the eye to follow a target.

[0004] 2. BACKGROUND TO THE TECHNOLOGY

[0005] The human eye is a complex and delicate organ used to perceive the world around us. The eye captures light and forms an image on the retina. This generates electrical signals which are transmitted to the brain and interpreted as visual information. Scientists and medical professionals have come to understand the importance of tracking eye movement in diagnosing and treating various medical conditions. In particular, the movement of the eye has been found to be a useful indicator of brain function, including the presence of certain medical conditions.

[0006] One example of a medical condition that the movement of the eye may be used to assess is traumatic brain injury, including mild traumatic brain injury (mTBI) or concussion. Mild traumatic brain injury is a complex neurobehavioral phenomenon caused by deformation of the brain tissue under acceleration of the head. This may also be caused by mechanical forces directly impacting the skull. It can cause a range of symptoms, including headaches, dizziness, fatigue, depression, anxiety, irritability, loss of consciousness and impaired cognitive function, which may last between days and years as microstructural damage to axons and neurometabolic changes result in brain network disruption. The impact of a concussion can affect the brain's ability to control eye movements, leading to symptoms such as double vision, blurred vision, and problems with coordination.

[0007] The diagnosis of a concussion may be based on a combination of self-reported symptoms, and physical and neurological examinations. One classic method is a physician asking the patient to look at their finger as they move it around and watch how the patient's eyes track the movement. Such methods can be subjective and prone to error, and may ideally require a clinical environment suitable for careful tests. There are many situations where a quick, accurate assessment of the likelihood of a concussion may be required away from clinical environments. Such situations include during play of a contact or combat sport, for example football (NFL, soccer, Australian rules), rugby, boxing, martial arts, etc, or at the scene of an injury, for example a road vehicle accident.

[0008] More reliable diagnosis methods like brain imaging such as CT and MRI scans require expensive, bulky equipment that is not portable and therefore not suitable for in situ diagnoses as required in the above situations.

[0009] Scientists are also increasingly understanding that other types of medical condition may also be assessed by observation of the movement of the eye.

[0010] One example of an existing system to help assess concussion is the EyeBOX® by Oculogica. This system requires a dedicated terminal which, although marketed as "portable", is the size of a computer screen. Another example is described in US Patent No. 10,849,492, however this device images the eye using the front facing wide angle camera of a smartphone held at arm's length. As a result the image of the eye is captured with few pixels which makes it difficult to accurately image and assess the eye's movement.

[0011] Other examples include AR / VR headsets. However in such headsets, cameras are positioned to image the eye at a position that is at a significant angle to the eye. This reduces the resolution of the captured images of the eye and makes assessment of eye movement less accurate.

[0012] There is a need for more tools that allow the evaluation of medical conditions through eye movement in a way that is more convenient, objective and / or accurate than certain existing diagnostic tools.

[0013] 3. OBJECT OF THE TECHNOLOGY

[0014] It is an object of the technology to provide an improved device, system and / or method for tracking movement of an eye.

[0015] Alternatively, it is an object of the technology to at least provide the public with a useful choice. 4. SUMMARY OF THE TECHNOLOGY

[0016] According to certain aspects of the technology, there is provided a device for tracking movement and / or determining the position of an eye or part thereof, for example in its ability to follow a target.

[0017] According to one aspect of the technology, there is provided a device for tracking movement of the eye, the device comprising a cylindrical lens and a linear camera for imaging the eye. The cylindrical lens and the linear camera may be positioned so that the linear camera images the eye through the cylindrical lens, the cylindrical lens being oriented substantially parallel to the linear camera. The device may further comprise a light source for illuminating the eye. In some forms, the device may comprise a display screen to show a target for viewing by the eye when the linear camera images the eye.

[0018] According to one aspect of the technology, there is provided a device for tracking movement of an eye. The device may comprise one or more light sources for illuminating the eye. The device may further comprise a first cylindrical lens and a first linear camera for imaging the eye. The first cylindrical lens and the first linear camera may be positioned so that the first linear camera images the eye through the first cylindrical lens. The first cylindrical lens may be oriented substantially parallel to the first linear camera. The device may further comprise a second cylindrical lens and a second linear camera for imaging the eye. The second cylindrical lens and the second linear camera may be positioned so that the second linear camera images the eye through the second cylindrical lens. The second cylindrical lens may be oriented substantially parallel to the second linear camera. The first cylindrical lens and the first linear camera may be oriented substantially non-parallel to the second cylindrical lens and the second linear camera.

[0019] In some forms, the first linear camera and the first cylindrical lens may be oriented substantially perpendicular to the second linear camera and the second cylindrical lens.

[0020] In some forms, the device may be configured so that, in use, the first linear camera and the first cylindrical lens are oriented perpendicular to the transverse (or horizontal) plane of the eye, and the second linear camera and the second cylindrical lens are oriented perpendicular to the sagittal plane (vertical) of the eye. In certain forms, the first and second linear cameras may be infrared-sensitive linear cameras. In some forms, the one or more light sources may comprise an infrared light source. In further forms, the one or more light sources may comprise two infrared light sources associated with each linear camera. One of the infrared light sources may be positioned either side of each linear camera. In some forms the one or more light sources may comprise one or more infrared LEDs.

[0021] In some forms, the one or more light sources may be adjustable in brightness. Additionally, or alternatively, the frequency of light produced by the one or more light sources may be adjustable.

[0022] In some forms, the eye tracking device may be configured so that light from one of the light sources is incident on the eye substantially along the optical axis of a respective one of the linear cameras.

[0023] In certain forms, the device may comprise a display screen positioned such that, in use, the eye can view the display screen. In certain forms, the display screen may be comprised as part of a first portable electronic device, for example a first smartphone.

[0024] In certain forms, the device may comprise a reflector. The display screen may be positioned relative to the reflector such that, in use, the eye views the display screen reflected in the reflector. At least one of the linear cameras may be positioned to image the eye through the reflector. For example, the reflector may comprise a one-way mirror.

[0025] In some forms, the reflector may comprise an opening and at least one of the linear cameras may be positioned to image the eye through the opening in use.

[0026] In alternative forms, the reflector may be semi-transparent and the device may be configured so that at least one of the linear cameras is able to image the eye through the reflector.

[0027] In certain forms, the reflector may have a reflective side and the reflective side may be concave in at least one plane.

[0028] In certain forms, the device may be configured such that the eye substantially fills the field of view of each linear camera. In certain forms, the device may include a housing adapted to provide a light-controlled environment.

[0029] According to one aspect of the invention, there is provided a processor-implemented method for determining the position of a pupil of an eye within a field of view of a camera. The method may comprise receiving a set of image data values, each value in the set representative of the total intensity of light from a respective slice of a plurality of parallel slices within the field of view. The method may further comprise analysing the set of image data values to determine the position of the pupil in a direction perpendicular to the orientation of the slices.

[0030] According to one aspect of the invention, there is provided a processor-implemented method for determining the position of a pupil of an eye within a field of view of a camera. The method may comprise receiving a first set of image data values, each value in the set representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view. The method may further comprise receiving a second set of image data values, each value in the set representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view. The method may further comprise analysing the first and second set of image data values to determine the position of the pupil.

[0031] According to one aspect of the invention, there is provided a processor-implemented method for tracking the movement of an eye within a field of view of a camera. The method may comprise receiving a first set of image data values, each value in the set representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view. The method may further comprise receiving a second set of image data values, each value in the set representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view. The method may further comprise analysing the first and second set of image data values to determine a position of the pupil at a first time. The method may further comprise repeating the previous steps at each of a plurality of times over a period of time to generate a set of pupil positions over the period of time. The method may further comprise analysing the set of pupil positions generated at the previous step to track the movement of the eye.

[0032] In certain forms, the first and second set of image data values received may be representative of a two dimensional image of the field of view, each value in the first set of image data values generated from a sum of light intensities in a column of the two dimensional image and each value in the second set of image data values generated from a sum of light intensities in a row of the two dimensional image.

[0033] In certain forms, the step of analysing the first and second set of image data values to determine the position of the pupil may comprise determining a location of one or more peaks and / or troughs in the first and second sets of image data values.

[0034] In certain forms, the step of analysing the set of pupil position values to track movement of the eye may comprise identifying changes in the pupil position values over the period of time and tracking the movement of the eye based on the changes over time.

[0035] In certain forms, the method may comprise the further step of providing data representing the tracking of the eye movement to a user interface for display to a user.

[0036] According to one aspect of the invention there is provided a system for determining the position of a pupil of an eye within a field of view of a camera. The system may comprise an image data generator for generating a first set of image data values, each value in the set representative of the total intensity of light from a respective slice of a plurality of parallel slices within the field of view. The system may further comprise a processor for analysing the set of image data values to determine a position of the pupil in a direction perpendicular to the orientation of the slices.

[0037] According to one aspect of the invention there is provided a system for determining the position of a pupil of an eye within a field of view of a camera. The system may comprise a first image data generator for generating a first set of image data values, each value in the set representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view. The system may further comprise a second image data generator for generating a second set of image data values, each value in the set representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view. The system may further comprise a processor for analysing the first and second sets of image data values to determine a position of the pupil.

[0038] In certain forms, the first and second image data generators may be configured to generate image data values at each of a plurality of times over a period of time to generate a set of pupil position values over time. The processor may be configured to analyse the set of pupil positions over the period of time to track the movement of an eye.

[0039] In certain forms, the system may further include a user interface for displaying data representing the eye tracking movement.

[0040] In certain forms the first and second image data generators may comprise two linear cameras oriented substantially non-parallel to each other. In some forms, the two linear cameras may be oriented substantially perpendicular to each other.

[0041] Further aspects of the technology, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the technology.

[0042] 5. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] One or more embodiments of the technology will be described below by way of example only, and without intending to be limiting, with reference to the following drawings, in which:

[0044] Figure 1A is a front view illustration of a human eye;

[0045] Figure IB is a cross-section of the eye 101 of Figure 1A in a sagittal plane;

[0046] Figure 2 is a schematic illustration of an eye tracking device according to one exemplary form of the technology;

[0047] Figure 2A is a schematic illustration of an eye tracking device according to a further exemplary form of the technology;

[0048] Figure 2B is a schematic illustration of an eye tracking device according to a further form of the technology;

[0049] Figure 2C is a schematic illustration of an eye tracking device according to a further form of the technology;

[0050] Figure 2D is a schematic illustration of an eye tracking device according to a further form of the technology;

[0051] Figure 3 is a schematic illustration of an eye tracking device according to a further exemplary form of the technology; Figure 4 is a schematic illustration of part of an eye tracking device according to a further exemplary form of the technology;

[0052] Figure 5 is a schematic illustration of part of an eye tracking device according to a further exemplary form of the technology;

[0053] Figures 6A-B are illustrations of movements of a target on a display screen according to certain forms of the technology;

[0054] Figures 7A-C are schematic illustrations of eye tracking devices according to further exemplary forms of the technology;

[0055] Figures 8A-B are schematic illustrations of an eye tracking device according to a further exemplary form of the technology;

[0056] Figure 9 is a schematic illustration of an eye tracking device according to a further exemplary form of the technology;

[0057] Figure 10 is a schematic illustration of an eye tracking system according to one exemplary form of the technology;

[0058] Figure 11 is a schematic illustration of an exemplary data analysis system according to one form of the technology; and

[0059] Figure 12 shows an example of an image of an eye captured by an eye tracking device according to one form of the technology, and two sets image data values related to the image.

[0060] 6. DETAILED DESCRIPTION OF EXEMPLARY FORMS OF THE TECHNOLOGY

[0061] 6.1. Eye

[0062] Forms of the technology are directed to devices, systems and methods for tracking movement of an eye, for example in the ability of the eye to follow a target. Some relevant aspects of the anatomy and movement of the eye will now be described. Forms of the technology are primarily concerned with tracking movement of a human eye although the technology may be applied to the eye of any animal.

[0063] In this specification, anatomical terms of location relative to the body may be used, for example "superior", "inferior", "anterior", "posterior", etc. These are used as convenient labels to provide clarity to the position of components in exemplary forms of the technology relative to the body of a patient or subject of the eye tracking assessment during use of the technology and to accommodate the prospect that the patient may not necessarily be in a vertical (e.g. standing) orientation when the technology is used. It should be understood that the use of these terms to describe the relative position of certain components does not require the device and its components to be so situated with respect to a body at all times. A device may be removed from proximity with the body and / or may be oriented differently while still existing as the same device and embodying certain forms of the technology.

[0064] 6.1.1. Anatomy of the Eye

[0065] Figure 1A is a front view illustration of a human eye 101, including eyeball 104 and pupil 106. Movement of the eye 101 may be characterised by movement of the eyeball 104 and / or the pupil 106 in two mutually perpendicular axes, for example an axis in the lateral direction relative to the body (i.e. the horizontal direction when the body is standing upright), illustrated as x-axis 107 in Figure 1A, and an axis in the superior-inferior direction relative to the body (i.e. the vertical direction when the body is standing upright), illustrated as y-axis 108 in Figure 1A. These axes are also illustrated on Figure IB, which is a cross-section of the eye 101 of Figure 1A in a sagittal plane (vertical when the body is standing upright).

[0066] 6.1.2. Movement of the Eye

[0067] Bodies have muscles that control movement of the eyeball 104. In the human eye 101, these are the extraocular muscles and the intrinsic eye muscles. The main function of the extraocular muscles, of which there are seven per eye, is to control eye movement and eye alignment. There are three intrinsic eye muscles per eye and they control movement of the lens and pupil dilation, which enable the eye to focus on near objects and control how much light enters the eye.

[0068] Multiple different types of eye movement have been characterised, including:

[0069] • Saccades - are rapid, ballistic movements of the eyes that abruptly change the point of fixation. They range in amplitude from, for example, the small movements made while reading to the much larger movements made while gazing around a room. Saccades can be elicited voluntarily, but occur reflexively whenever the eyes are open, even when fixated on a target;

[0070] • Microsaccades - are a kind of fixational eye movement. They are small, jerk-like, involuntary microscopic eye movements, similar to miniature versions of voluntary saccades. They typically occur during prolonged visual fixation to prevent fading; • Square-wave jerk - a form of fixational eye movement which move away and back from a fixation at equal magnitudes, occurring within approximately 200-500 ms;

[0071] • Prosaccades - a saccade towards a target, generally reflexively generated;

[0072] • Antisaccade - a saccade away from a target, generally volitionally generated;

[0073] • Drift - the brain mechanisms behind ocular drifts are not fully known, but these are slower, more gradual movements that take place between microsaccades, during fixation;

[0074] • Tremor - small, high-frequency perturbations that take place between microsaccades;

[0075] • Fixational eye movements: for example microsaccades, square-wave jerks, tremor, and drift;

[0076] • Fixation: a fixation is composed of slower and minute movements (fixational eye movements) that help the eye align with the target and avoid perceptual fading. The duration may vary between, for example 50-600 ms; and

[0077] • Smooth pursuits: these are movements that are much slower tracking movements of the eyes designed to keep a moving stimulus on the fovea. Such movements are under voluntary control in the sense that the observer can choose whether or not to track a moving stimulus and occur between saccades.

[0078] Forms of the technology may be used to track any one or more of these types of eye movement.

[0079] Eye movement dysfunction occurs when there is some abnormality or impairment of normal eye movement, for example saccades and smooth pursuits may be inaccurate with reference to a target, or may be interrupted in motion or irregular in timing. Saccade dysmetria is a motor error resulting in over or under shoot of the eye to the target accompanied by corrective saccades. Certain measures may be used to quantify eye movement dysfunction, for example saccade gain is the ratio of the eye movement to target location, and stimulus delay is the delay in reaction before the onset of the motor command when stimulus in the form of a target is presented in the visual plane.

[0080] 6.1.3. Eye Tracking

[0081] Forms of the technology relate to devices, systems and methods for "tracking" movement of the eye 101. Unless the context clearly indicates otherwise, the term "tracking" is intended to mean the act of identifying the way in which the eye 101 moves over a period of time. By identifying movement of the eye 101, the movements may be able to be characterised and analysed. In certain forms, movement of the eye 101 is tracked by observing movement of the pupil 106. The pupil 106 is the aperture through which light enters the internal parts of the eye 101 and its position is therefore indicative of the direction of the eye's vision. The eye is tracked in its ability to follow a target, for example which moves on a display screen presented to the eye. Any errors in tracking the target may be characterised and analysed.

[0082] 6.2. Eye Tracking Device

[0083] There will now be described exemplary forms of devices 200 and / or systems 300 for tracking movement of an eye according to certain forms of the technology. Such devices / systems may otherwise be referred to as eye tracking devices 200 / systems 300. The device / system according to certain forms of the present technology utilises a linear camera in conjunction with a cylindrical lens to measure the position of an illuminated pupil along an axis. By combining data produced by multiple linear cameras along different axes, eye pupil position at a point in time, and therefore eye tracking over time, can be established.

[0084] 6.2.1. Components of Eye Tracking Device / System

[0085] Some components common to several of the exemplary forms of the technology will now be described. It will be understood that, where these components are later described in the context of particular forms of eye tracking devices / systems, the description of the components in this section applies to any of the forms of the technology unless explicitly stated otherwise. In certain forms of the technology, the eye tracking system 300 may be any assembly of components that is configured to track movement of an eye 101 and to output data representative of the movement of the eye 101.

[0086] 6.2.1.1. Camera(s)

[0087] In certain forms of the technology, for example as shown in Figures 2 to 5 and 7A to 10, the eye tracking device 200 comprises one or more camera(s) 220 / 221. In some forms, the camera(s) comprise at least two linear cameras, for example the two linear cameras 220 and 221 shown in Figure 2. The linear cameras 220 and 221 may comprise any optical device configured to capture and record lines of pixels in one dimension, and may alternatively be referred to as line-scan cameras. In certain forms the linear cameras are infrared-sensitive linear cameras. Such cameras may be used in forms of the technology in which the eye 101 is illuminated by infra-red light. The two cameras 220 and 221 may be controlled to capture images at substantially the same time.

[0088] In other forms of the technology, for example as shown in Figure 10, the eye tracking device 200 may comprise a single camera 220. The camera 220 may comprise any optical device configured to capture and record two-dimensional visual images.

[0089] In some forms, the captured image data may be displayed on a display screen, which in some forms may be comprised as part of the eye tracking device 200, while in other forms the cameras may be configured to transmit the image data to another device, which may itself comprise a display screen for displaying the images or a memory for storing the image data for analyses and display elsewhere. The image data may be transmitted through a wired or wireless connection, for example to a display screen located remote from the eye tracking device 200. The image data may be displayed on the display screen in real-time, near-real-time, or at a later time compared to when the images are captured by the camera. In some forms, the cameras 220 and 221 may each comprise a memory configured to store the image data. It should be appreciated that the cameras 220 and 221 may be digital cameras and reference to images may mean the data recorded by the cameras as being representative of the image.

[0090] 6.2.1.2. Cylindrical Lens

[0091] In certain forms of the technology the device comprises at least two cylindrical lenses 206 and 207, one lens associated with each of the linear cameras 220 and 221. A cylindrical lens has differing radii in mutually perpendicular directions (e.g. the X and Y axes), focussing the light passing through the lens substantially into a line. In some forms, the cylindrical lenses 206 and 207 may be in the shape of cylinders, but in other forms other shapes may be used, including plano-convex, plano-concave, round or oblong cylindrical lenses. In some forms, the radius of curvature of the lens in one of the mutually perpendicular directions may be substantially infinite, i.e. the lens may not curve in one direction.

[0092] 6.2.1.3. Light Source

[0093] In certain forms, the eye tracking device 200 may comprise one or more light sources 350. The light sources 350 may be positioned and arranged to illuminate the eye 101 sufficiently for imaging by the camera(s) 220 / 221. In some forms, the light source(s) 350 may be a source of infrared light, for example with wavelengths outside the visible spectrum in the range 750 nm - 1000 pm. Infrared light may be particularly suitable for forms of the technology that rely on identifying the position of the pupil 106 of the eye 101 from light reflected from the fundus. At infrared wavelengths, the eye exhibits the "bright eye effect" where pupils may reflect almost all the IR light they receive back. In some forms, the one or more light sources 350 may produce light with a wavelength of 780 nm, since this was found in some experiments to provide the brightest illumination of the pupil when imaged. The light source(s) 350 may comprise one or more infrared LEDs, illuminators or lamps.

[0094] The light source(s) may be located at a position suitable to brightly illuminate eye 101, in particular the pupil 106, during use of the device 200. To utilise the bright eye effect of infrared light to a sufficient degree to identify the position of the pupil 106, in some forms, the eye tracking device 200 may be configured so that the illumination of the eye 101 is substantially axial with respect to the camera 220, i.e. light from one of the light sources 350 is incident on the eye 101 substantially along the optical axis of the respective camera 220. Exemplary arrangements that may achieve this are described below. In certain forms, one of the light sources 350 may be positioned proximate the optical axis of each of the cameras 220. For example, the light source 350 may be positioned within approximately a 0° - 20° offset from the optical axis of the respective camera. In some forms the infrared light source is within 0° - 5° offset from the optical axis of the camera. The closer the light source is to the optical axis of the camera, the better the bright eye effect, and therefore light reflection to the camera, may be. It will be appreciated that, the closer the light source 350 is to the eye 101, the closer the light source 350 needs to be positioned to the optical axis in order to achieve the same angular offset.

[0095] In other forms, the light source(s) 350 may be a source of light in the optical region of the spectrum. In such forms, the light source 350 may comprise the first display screen 210 that is also configured to display gaze targets to the user (as described below).

[0096] In certain forms, the light source(s) 350 may be adjustable in brightness.

[0097] In certain forms, the light source(s) may be sources of diffuse light. To illuminate the eye 101 with diffuse light, the device 200 may comprise one or more diffusers. Each diffuser may be positioned in front of one or more of the light sources 350 in order to diffuse the light emitted by the light sources. Additionally, or alternatively, in certain forms, the frequency of light produced by the light sources may be adjustable. For example, the light source may be configured to selectively generate light of one or more parts of the infrared spectrum. Changing the frequency of the light may be useful to generate different types of reflection from pigments in the iris, which may be desired for certain types of analysis of the eye 101.

[0098] 6.2.1.4. Reflector

[0099] In certain forms of the technology, the eye tracking device 200 may comprise a reflector 230. The reflector 230 is a structure able to reflect light incident on the reflector.

[0100] The reflector 230 may comprise a reflective side 232 which in certain forms may comprise a mirror. As will be explained, in some forms of the technology, the reflector 230 may at least in part comprise a one-way mirror (which may also be referred to as a half-silvered or semi-transparent mirror) such that the reflector 230 reflects light incident on the reflective side 232 but transmits light incident on another side. In other forms, the reflector 230 may comprise a prism configured to reflect incident light.

[0101] As will be explained in more detail further below, in some forms the reflector 230 may be non-planar, or curved, for example concave in at least one plane.

[0102] 6.2.1.5. Display Screen

[0103] In certain forms of the technology, the eye tracking device 200 may comprise one or more display screens, for example first display screen 210 and second display screen 211. The display screens 210, 211 may comprise any device configured to present information visually to a viewer. The information may be in the form of images, for example. The display screens 210, 211 may be controllable to alter the information displayed to the viewer. For example, a moving target may be displayed to the viewer and may follow different testing protocols such as described in more detail later. The range of ocular motion may be important in detecting some medical conditions, so in certain forms the display is positioned to occupy over 100° of the field of view and, in some forms, the eye tracking device may be configured so that the display occupies approximately 120° of the field of view. This means the target may be moved on the display so the viewer must move their eye larger distances to follow the target's movement (e.g. up, down, left and right).

[0104] In certain exemplary forms, one or more of the display screens 210, 211 are an electronic display, for example an LCD, LED, OLED screen. The information displayed on the display screens 210, 211 may be controllable by a controller or microprocessor, which may be comprised as part of the display screen 210, 211, or may be configured to control the display screen 210, 211 through a physical or wireless connection. In some forms, the display screen 210, 211 is comprised as part of an electronic device, for example a portable electronic device 250 such as a smartphone, tablet, laptop computer or the like.

[0105] In some forms, each of the display screens 210, 211 may be self-illuminating, for example the display screen 210, 211 may comprise light-emitting elements such as LEDs. In other forms, either or both of the display screens 210, 211 may be non-self-illuminating, for example the display screen may display information using electronic ink (e-ink). In such forms, a separate light source may be used to illuminate the display screen.

[0106] 6.2.1.6. Data Analysis System

[0107] Figure 11 is a schematic illustration of an exemplary data analysis system 400 according to one form of the technology. Data analysis system 400 may comprise a hardware platform 402 that manages the collection and processing of data from eye tracking system 300, for example the data representative of the movement of the eye 101 and the data representative of the movement of the target 303. The hardware platform 402 may comprise a processor 404, memory 406, and other components typically present in such computing devices. The hardware platform 402 may be local to the eye tracking system 300 or it may be remote from the eye tracking system 300 and receive the data over a suitable communications link, such as network 416. In the exemplary form of the technology illustrated, the memory 406 stores information accessible by processor 404, the information including instructions 408 that may be executed by the processor 404 and data 410 that may be retrieved, manipulated, or stored by the processor 404. The memory 406 may be of any suitable means known in the art, capable of storing information in a manner accessible by the processor 404, including a computer-readable medium, or other medium that stores data that may be read with the aid of an electronic device. The processor 404 may be any suitable device known to a person skilled in the art. Although the processor 404 and memory 406 are illustrated as being within a single unit, it should be appreciated that this is not intended to be limiting, and that the functionality of each as herein described may be performed by multiple processors and memories, that may or may not be remote from each other or from the processing system 400. The instructions 408 may include any set of instructions suitable for execution by the processor 404. For example, the instructions 408 may be stored as computer code on the computer-readable medium. The instructions may be stored in any suitable computer language or format. Data 410 may be retrieved, stored or modified by processor 404 in accordance with the instructions 410. The data 410 may also be formatted in any suitable computer readable format. Again, while the data is illustrated as being contained at a single location, it should be appreciated that this is not intended to be limiting - the data may be stored in multiple memories or locations. The data 410 may also include a record 412 of control routines for aspects of the system 400.

[0108] The hardware platform 402 may communicate with a display device 414 to display the results of analysing the data. In some forms, the display device 414 may be the display screen 320 that is comprised as part of eye tracking system 300. The hardware platform 402 may communicate over a network 416 with one or more other devices (for example user devices, such as a tablet computer 418a, a personal computer 418b, or a smartphone 418c, or other devices including sensors), or one or more server devices 420 having associated memory 422 for the storage and processing of data collected by the local hardware platform 402. It should be appreciated that the server 420 and memory 422 may take any suitable form known in the art, for example a "cloud-based" distributed server architecture. The network 416 may comprise various configurations and protocols including the Internet, intranets, virtual private networks, wide area networks, local networks, private networks using communication protocols proprietary to one or more companies, whether wired or wireless, or a combination thereof.

[0109] Following analysis of the data representative of the movement of the eye 101, the data analysis system 400 may be configured to output certain information gained from the analysis process, examples of which will be described in more detail below. The information may be output by the data analysis system 400 by sending the information over network 416 or by outputting the information via an output device, for example display device 414, tablet computer 418a, personal computer 418b, or smartphone 418c. Alternatively, the information may be stored in a memory, for example one or both memory 406 or 422, for later outputting from the data analysis system 400. In certain forms, the hardware platform 402 of data analysis system 400 may comprise a computing device, for example a laptop or PC. In other forms, the hardware platform 402 may comprise a plurality of computing devices configured to operate collectively to perform the data analysis / processing.

[0110] 6.2.2. Exemplary Forms of Eye Tracking Device - Linear Cameras & Cylindrical Lenses

[0111] Figure 2 is a schematic illustration of an eye tracking device 200 according to one exemplary form of the technology. The eye tracking device 200 comprises two linear cameras 220 and 221. The device is configured so that, in use, the linear cameras are positioned to image the eye 101. The linear cameras may be oriented at a non-zero angle relative to each other, i.e. so that the linear cameras 220 and 221 are oriented substantially non-parallel to each other. In this specification, unless the context clearly indicates otherwise, reference to the orientation of a linear camera should be understood to mean the orientation of the axis along which the linear camera records a line of pixels.

[0112] In some forms, the linear cameras 220 and 221 are oriented substantially perpendicular to each other. In some forms, the eye tracking device 200 may be configured so that, in use, a first linear camera 220 is oriented perpendicular to the transverse (or horizontal) plane of the eye, and a second linear camera 221 is oriented perpendicular to the sagittal (vertical) plane of the eye.

[0113] A configuration in which the linear cameras are oriented non-parallel to each other enables the image data to be interpreted in two different directions, and for this to be used to ascertain information on the direction of the gaze of the eye in two-dimensions, as explained below. A configuration in which the linear cameras 220 and 221 are substantially perpendicular to each other enables simultaneous capture of image data of the eye in mutually perpendicular directions, which may improve information on the pupil position that can be ascertained. The device 200 may be configured so that the linear cameras 220 and 221 capture any desired width or height of pixels in the orientation of the respective camera required to image the eye 101 including the pupil 106.

[0114] In certain forms, such as shown in Figure 2, two cylindrical lenses 207 and 206 are positioned between linear cameras 220 and 221 and the eye respectively such that light entering the linear cameras passes through one of the cylindrical lenses. Each cylindrical lens may be positioned and oriented to focus incoming light onto the sensor of the respective linear camera. Consequently, as shown in Figure 2, each cylindrical lens 206 and 207 may be oriented substantially parallel to the respective linear camera 220 and 221 into which it focuses light.

[0115] Since the cylindrical lenses are arranged substantially parallel to the linear cameras, the comments above on the non-parallel arrangement of the linear cameras relative to each other also apply to the arrangement of the cylindrical lenses relative to each other. That is, in certain forms, the cylindrical lens 206 is oriented substantially non-parallel to the cylindrical lens 207. For example, the cylindrical lens 206 may be arranged substantially perpendicular to the cylindrical lens 207. In certain exemplary forms of the device 200 may be configured so that, for example as shown in Figure 2, cylindrical lens 207 is oriented perpendicular to the transverse (horizontal) plane of the eye and cylindrical lens 206 is oriented perpendicular to the sagittal (vertical) plane of the eye in use. In other forms, the eye tracking device 200 may comprise three or more cylindrical lens / linear camera assemblies, with each assembly oriented at angles relative to the other assemblies. For example, in the case of three assemblies, they may be oriented at 120° to each other. However, it may be challenging to position too many lenses and cameras sufficiently close to the eye in appropriate orientations.

[0116] One or more light sources 350, for example infrared light sources in the form of LEDs, illuminate the eye 101 from a position suitable to sufficiently illuminate the eye for capturing images with linear cameras 220 and 221. In the exemplary forms of Figure 2, a pair of light sources 350 is associated with each linear camera. In some forms, positioning the light sources 350 close to, for example immediately adjacent to, the camera and / or respective cylindrical lens may enhance the amount of IR illumination passing through the pupil due to reflection off the fundus. For example, the IR LEDs may be positioned proximate to, for example immediately adjacent to, and optionally on opposing sides of, cylindrical lenses 206 and 207. This may enhance the bright eye effect, enabling more accurate measurement of the pupil position based on light reflected from the pupil. In other forms, a single light source 350 may be used, or a single light source 350 may be associated with (e.g. positioned proximate) each camera. The single light source 350 may be positioned proximate to, for example immediately adjacent to, the camera and / or respective cylindrical lens. Alternatively, the eye tracking device 200 may be configured so that the light source provides axial illumination, such as described further below.

[0117] In use, light from the light source 350 is reflected off the fundus at the back of the eye 101, passing through the pupil, and the reflected light is focussed by cylindrical lenses 206 and 207 onto the sensor of the respective linear camera 221 and 220. The resultant image data generated by each linear camera represents a one-dimensional line of light intensities across the field of view of the camera. The cylindrical lens acts to sum the intensities of light in slices of the field of view in a direction perpendicular to the orientation of the lens, e.g. a horizontally-oriented cylindrical lens 206 acts to sum the intensities of light in vertical columns of the field of view onto the pixel sensor of the linear camera 220 that receives light from that vertical column of the field of view. Similarly, a vertically-oriented cylindrical lens 207 acts to sum intensities in horizontal rows of the field of view for detection by the sensor of the linear camera 221. Simultaneous operation of the first and second linear cameras results in image data values being collected in two different directions, e.g. two mutually perpendicular directions, from the field of view, which contains the eye 101 in use.

[0118] Eye tracking devices 200 according to forms of the technology similar to that of Figure 2 are also shown in Figures 2A and 2B.

[0119] In some forms, for example as shown in Figures 3 to 5 and 7A to 10, an eye tracking device 200 may comprise a display screen 210. The eye tracking device 200 may be configured to position the display screen 210 so that an eye 101 may view the display screen 210 and the camera 220 may image the eye when the eye is viewing the display screen. In at least one example the relative positioning of the display screen, camera and eye is such that the camera tracks the eye movement as it follows a target at substantially the same angle as the direction of the eye's gaze, thus giving accurate real-time data useful to detect medical conditions linked to delayed or erratic eye movement. Examples of how an eye tracking device 200 may be configured to position a display screen 210 suitably are described below.

[0120] In some forms of the technology in which the eye tracking device 200 comprises linear cameras 220 and 221, such as described above, the eye tracking device 200 may further comprise an additional camera 222 (not illustrated) configured to capture two-dimensional visual images of the eye 101 while the linear cameras 220 and 221 are also capturing images of the eye 101. In some forms, the 2D camera 222 is capable of capturing images with a sufficiently fast frame rate for the images to be considered to capture video footage of the eye, for example in some forms the 2D camera may capture images at a frame rate of approximately 500 fps or faster. Images captured by the 2D camera 222 may be viewed in real-time, i.e. simultaneously with images of the eye 101 being captured by the linear cameras 220 and 221, for example viewed on display screen 211, so that a user can view the eye 101 during the eye tracking process to ensure that the process is being conducted as intended. Alternatively, images captured by the 2D camera 22 may be viewed at a later time, i.e. after images of the eye 101 are captured by the linear cameras 220 and 221, for example on display screen 211 or on any of the display devices of data analysis system 400, such as display device 414. Viewing images captured by 2D camera 222 may additionally or alternatively be useful if any difficulties are caused in the determination of the position of the pupil and / or eye tracking if the eye 101 adopts a wide ocular pose, i.e. a direction of gaze that is at a significant angle compared to the direction of the cameras 220 / 221. In such a scenario, the amount of light reflected back from the eye 101 towards the cameras 220 / 221 may be lessened, and possibly to a sufficient extent to impact on the ability to determine the position of the pupil or track the eye. As explained below, illuminating the eye 101 substantially axially with respective to the optical axis of the cameras 220 / 221 may avoid this issue.

[0121] 6.2.3. Exemplary Forms of Eye Tracking Device - 2D Image Capture

[0122] Another form of eye tracking device 200 is illustrated in Figure 10. The eye tracking device 200 comprises a display screen 210 and a camera 220. The camera 220 in this form may comprise any optical device configured to capture and record two-dimensional visual images. In the illustrated form, both display screen 210 and camera 220 are comprised as part of a portable electronic device 250, for example a smartphone or tablet, although in other forms the display screen 210 and camera 220 may be provided as separate components. The device 200 is positioned so that an eye 101 may view the display screen 210 and the camera 220 may image the eye 101 when the eye is viewing the display screen 210.

[0123] This configuration is simple and may require only a single device, for example a smartphone or tablet, to implement the eye tracking system. However, imaging of the eye 101 may be low resolution because the device needs to be held sufficiently far from the eye for the patient to be able to focus on the display screen 210. A typical mature human eye may find it difficult to focus on anything that is closer than approximately 200 mm from the eye. At this range, the camera on a typical smartphone or tablet would image the eye 101 with only a subset of the available imaging field of view, which may not provide high enough resolution for detailed eye tracking, particularly of some of the smaller movements described above. On the other hand, positioning the display screen 210 further from the eye 101 constrains the range of the motion the eye exhibits in following a target on the display screen because the display screen occupies a smaller proportion of the field of view of the eye the further it is positioned from the eye. Symptoms of some medical conditions may require a full ocular range of eye movement to be exhibited. In addition, in this form of the technology, ambient light illuminates the eye 101 and the variable intensity and quality of ambient light may affect imaging quality. This section has described several forms of eye tracking device 200 which comprise a camera 220 that captures two-dimensional images, as distinct from the forms of the previous section in which the eye tracing device 200 comprises two linear cameras. Exemplary methods of eye tracking based on two- dimensional image data obtained using such exemplary devices will be explained below.

[0124] 6.2.4. Schematic Layout of Eye Tracking Device Comprising a Display Screen

[0125] It has been described that a display screen may be used to present information visually to a viewer for the purposes of eye tracking, e.g. a moving target may be displayed for the user to follow with their gaze. In some forms, the display screen may be provided separate to the eye tracking device 200. In other forms, the display screen 210 may be comprised as part of the eye tracking device 200. Exemplary such forms of the technology will now be described.

[0126] In some forms of the technology, the eye tracking device 200 comprises a reflector 230, as exemplified in Figures 2A to 2D, 3, 4, 5, 7A, 7B and 7C. This advantageously enables the optical distance from the eye 101 to the display screen 210 to be increased, while maintaining the camera(s) 220 / 221 at a position to image the eye 101 at relatively close proximity and consequently with high resolution. It should be understood that, in all of the forms of technology shown in these figures, the depicted camera may take the form of two linear cameras 220 and 221, such as described in relation to the form of Figure 2, or may be a single two-dimensional camera 220. Reference to "camera 220" in this section of the description may therefore be interpreted to alternatively refer to "cameras 220 and 221" in other forms. The method of processing image data from the camera(s) may differ between these two sets of examples, as described in more detail below.

[0127] As shown in Figures 3, 4, 5, 7A to 9, the eye tracking device 200 comprises a display screen 210. A display screen 210 may also be present in the forms shown in Figures 2A and 2B, despite it not being shown in the figures. The display screen 210 is positioned relative to the reflector 230 such that, in use, the eye 101 views the display screen 210 reflected in the reflector 230, as shown by the rays indicated in Figures 7A to 7C. In the forms shown in Figures 3, 4, 5 and 7B, the display screen 210 may be comprised as part of a portable electronic device 250, which is positioned proximate a patient's body with the display screen 210 facing away from the patient. The reflector 230 is positioned anterior to the eye 101 and further from the patient than the display screen 210. The display screen 210 and reflector 230 are positioned and oriented to enable the eye 101 to view a reflection of the display screen 210 in the reflector 230, i.e. so that light emitted by the display screen 210 reflects off a reflective side 232 of the reflector 230 and is incident on the eye 101. In the illustrated form, the reflector 230 is oriented with a reflective side 232 facing generally towards the display screen 210 and eye 101, i.e. the display screen 210 and eye 101 are positioned on the same side of the reflector 230.

[0128] As shown schematically in Figures 3 to 5, during use, the display screen 210 may be positioned superior to the eye 101. For example, the display screen 210 may be positioned anterior to (e.g. directly in front of) the patient's forehead. The display screen 210 may be tilted accordingly to enable the eye 101 to view the display screen 210 on reflection from the reflector 230, for example as shown in Figures 3 to 5, the superior end of the display screen 210 may be positioned more anteriorly (i.e. further from the patient's body) than the inferior end of the display screen 210. In other forms, the display screen 210 may be positioned in a different position and / or in a different orientation. For example, in some forms, the display screen 210 may be positioned inferior to the eye 101, for example directly anterior to the patient's cheek. In other forms, such as shown in Figures 7A, 7C and 8A, the display screen 210 may be positioned at a similar distance in front of the patient's body as the reflector 230 and may be located directly superior to, or inferior to, the reflector 230. It will be appreciated that, irrespective of the position of the display screen 210, it is oriented appropriately so that the eye 101 may view what is displayed on the screen as reflected in the reflector 230. For example, in the case of the display screen 210 being located directly superior to the reflector 230 such as shown in Figures 7A and 7C, the display screen 210 is oriented with the plane of the screen generally parallel to the patient's transverse (or horizontal) plane and with the display screen 210 facing in the inferior direction towards the reflector 230 which is positioned directly inferior to it.

[0129] In certain forms, for example as shown in Figures 2A to 5 and 7A to 7C, the reflective side 232 of the reflector 230 may be concave. The concave shape of the reflective side 232 may assist in reflecting light from the display screen 210 into the eye 101. This shape may also assist in keeping the overall size of the device 200 relatively compact, e.g. allowing the viewer to focus on the display 210 while still enabling all of the display screen 210 to be in focus with a wide field of view, for example of over 100°, for example 120°. That is, the concave reflector 230 makes the display screen 210 appear further away to the eye 101, and easier to focus on compared to its actual distance. For example, in certain examples, the reflective side 232 of the reflector 230 may be positioned approximately 40-80 mm, for example 60 mm, from the eye 101 during use. The display screen 210 may be positioned at approximately a similar distance from the reflector 230 during use. The optical properties of the reflector 230 may resolve the image in a way it is in focus for a wide field of view of the eye 101, for example approximately 100° degrees or more, which may enable testing the viewer's ocular range.

[0130] In some forms of the technology, the reflector 230 may be concave in multiple planes while in other forms of the technology, the reflector 230 may be concave in a single plane. For example, the schematic illustrations of the devices 200 in Figures 2A to 2D, 4, 5 and 7A to 7C show a cross-section of the reflector 230 through a first plane which is oriented parallel to a sagittal (or longitudinal) plane of the body when the device 200 is in use. The reflector 230 has a concave cross-section in this first plane. A second plane may be oriented perpendicularly to the first plane, for example the second plane may be horizontally oriented, or parallel to a transverse (or horizontal) plane of the body. In this second plane, the reflector 230 may also be concave, or the reflector 230 may have a straight cross-section. In the example of Figure 3, the reflector 230 is also concave in this second plane.

[0131] In certain forms in which the reflector 230 is concave, the surface of the reflector may, in part, form part of the surface of an asphere to reflect the flat display suitable for a spherical human eye. Another part of the surface of the reflector, or in other forms all of the surface of the reflector, may form part of the surface of a paraboloid, for example to reflect the part of the display which is off-axis to the human eye. In one example, a central region of the reflective side 232 of the reflector 230 has the shape of a radially distributed asphere. For example, the aspherical surface may be an axially symmetric quadric surface. This may help the eye 101 to focus on the flat plane of the display screen 210, despite the centre of the display screen 210 being closer to the eye 101 than the edges of the display screen 210. The asphere may also help reduce or eliminate spherical aberration and other optical aberrations such as astigmatism, when compared to a more simple shape for the reflector. In addition, top and bottom (i.e. inferior and superior) regions of the reflective side 232 may have a curvature increasing progressively towards the edge of the reflector 230, e.g. the surface of a paraboloid. The light from the display screen 210 reflects off the reflector 230 and the eye 101 is therefore a different distance away from the top of the screen compared to the bottom of the screen. The paraboloid shape translates the different light paths between the eye 101 and different parts of the display screen 210 into a common focus.

[0132] In certain forms of eye tracking device 200, for example as shown in Figures 2A to 5, 7A to 7C and 8A to 9, the camera 220 is positioned to image the eye 101 through the reflector 230. In this context, "through the reflector" means that the camera 220 is positioned on the other side of the reflector 230 to the eye 101, i.e. more anteriorly than the reflector 230, so that light from the eye 101 passes from one side of the reflector 230 to the other side of the reflector 230 before being captured by camera 220 (as opposed to referring to light reflected by the reflector).

[0133] The camera 220 may view the eye 101 through the reflector 230 in different ways in different forms of the technology. For example, in the forms shown in Figures 2A, 2C, 4 and 7A, the reflector 230 comprises an opening 234, which may take the form of a small hole through the reflector 230. The opening 234 may be large enough for the camera 220 to image the eye 101 through the opening 234 without the reflector 230 obstructing its field of view but may be no larger than necessary to achieve this. The smaller the size of the opening 234, the less the opening obstructs the eye's view of the display screen 210 in the reflector 230.

[0134] In another example, such as in the form shown in Figures 2B, 2D and 5, the reflector 230 may be semitransparent and the device 200 may be configured so that a linear camera 220, positioned on the opposite side of the reflector 230 to the eye 101, is able to image the eye 101 through the reflector 230 (i.e. with light from the eye 101 passing through the reflector 230) and the eye 101 is able to view the display screen 210 reflected in the reflector 230 (i.e. with light from the display screen 210 being reflected by the reflector 230). It should be understood that "transparent" in this context is intended to refer to the ability for light to pass through the material forming the reflector 230, as contrasted to the reflector 230 having an opening through which light may pass, as in the form of Figure 2A, 2C, 4 or 7A.

[0135] In some forms, all of the reflector 230 may be semi-transparent, while in other forms, one part of the reflector 230 may be semi-transparent, i.e. the region of the reflector 230 through which the camera 220 views the eye 101. It should be understood that the device may be configured so that the lighting conditions on either side of the reflector 230 may enable the reflector to function in this semitransparent way, for example with the lighting on the posterior side of the reflector 230 (i.e. the space between the reflector 230 and the eye 101) being relatively bright compared to the lighting on the anterior side of the reflector 230 (i.e. the space between the reflector 230 and the camera 220). Suitable lighting conditions may be established by provision of a housing 262 to house the components of the device in a light-controlled environment, as will be explained later. In certain forms, the reflector 230 may comprise a one-way mirror, which may alternatively be referred to as a half-silvered mirror. In some forms, the mirror may be front-silvered from the perspective of the display screen 210 (i.e. the reflective side 232 may be silvered), and the rear surface (i.e. the surface of the reflector 230 opposite the reflective side 232) may be coated with an antireflective tint. This may help to reduce chromatic aberration and to reduce ghosting from the image on the display screen 210 that the light refracts from air into the mirror material and then back to air.

[0136] For the purposes of analysing movement of the eye, it is helpful for the camera 220 to capture images of the eye 101 that have the highest resolution and highest frame rate possible within the limits of the physical and optical configuration of the device 200. To strive to achieve this, the device 200 may be configured such that, when viewing the display screen 210, the eye 101 substantially fills the field of view of the camera 220, for example as shown by the indicative light rays in some of the figures. In certain forms, the device 200 may further comprise one or more lenses 209, which may include cylindrical lenses 206, 207, positioned so that the camera 220 images eye 101 through the one or more lenses. For example, the lenses 209 may be positioned directly in front of the camera 220. In the examples of Figures 4 and 7A, the cylindrical lenses 209 are positioned in the opening 234, although it may alternatively be positioned anterior of the reflector 230, i.e. between the reflector 230 and the camera 220. In the example of Figure 5, the lenses 209 are positioned anterior of the reflector 230, i.e. between the reflector 230 and the camera 220. In some forms, the lenses 209 may be provided as part of the camera 220. In some forms, the one or more lenses 209 may comprise a macro lens. This may assist the camera to have the necessary field of view for the eye 101 to fill the field of view of the camera 220. In the case of a dedicated camera sensor then a suitable lens may be selected to allow for the focal range of the position of the viewer's eye relative to the camera, e.g. 40 - 80 mm from the eye in some examples.

[0137] In the example of using one typical model of linear camera 220, the camera 220 may have a sensor of approximately 2000 pixels wide along the optical axis of the linear camera. If the device 200 is configured so that the eye 101 substantially fills the field of view then, based on a typical eye width of 24.2 mm, each pixel images a part of the eye of 12.6 microns at the centre of the field of view. Greater accuracy may be achieved through image processing methods, for example subpixel tracking. In comparison, a typical microsaccade may be as small as 15 minutes of arc or 0.25°. For an eyeball of width 24.2 mm, this amounts to approximately 53 microns. Consequently, a pixel resolution of less than this may be necessary to successfully track some small eye movements such as microsaccades.

[0138] In the examples of Figures 2 to 5 and 7A to 10, the eye tracking device 200 is configured so that, during use, the camera 220 is positioned substantially directly in front of, i.e. directly anterior to, the eye 101. This may assist with obtaining a clear image of the eye and having the eye fill the field of view of the camera 220. In other forms, the camera 220 may be positioned at another position relative to the eye 101 in use, for example inferior to the eye.

[0139] In the forms of the technology shown in Figures 7A, 7C and 8A, the display screen 210 is positioned substantially horizontal with respect to the eye 101. That is, with respect to the body of the subject of the eye tracking, when the eye tracking device 200 is in use, the display screen 210 may lie substantially parallel to the horizontal plane (which may also be referred to as the transverse plane) of the body. In this form, the camera 220 may be positioned substantially directly in front of, i.e. directly anterior to, the eye 101. This may enable the camera 220 to be positioned such that the optical axis is / are substantially parallel or perpendicular to the plane of the display screen 210. This arrangement may facilitate positioning the display screen 210 and the camera 220 in a frame, since it may simplify the manufacture of a frame that holds all components substantially perpendicular or parallel to each other.

[0140] In a form of the technology such as is shown in Figures 7A, 7C and 8A where the display screen 210 is positioned substantially horizontal with respect to the eye 101, the reflector 230 may be suitably configured to reflect light from the display screen 210 to the eye in a manner that enables the eye 101 to see the display screen 210 as a substantially undistorted planar image. It will be appreciated that, in this orientation, the distances between different part of the display screen 210 and the reflector 230 may vary, for example an anterior portion of the display screen 210 distal from the eye 101 may be closer to the reflector 230 than a posterior portion of the display screen 210 proximal to the eye 101. In certain forms, a reflector 230 in the form of an asphere modified with a linear parabola may achieve this outcome. The schematic drawing in Figure 7C illustrates some different shapes of reflector 230 in such a configuration. Reflector 230a has an aspherical surface and reflector 230b has a linear vertical parabolic surface, i.e. the parabolic shape may be present in the vertical cross-section such as shown in Figure 7C (i.e. a cross-section parallel to the mid-sagittal plane of the body of the user) but may or may not be present in a horizontal cross-section (i.e. a cross-section parallel to the transverse plane of the body of the user). Reflector 230c has a surface that is a combination of these two, i.e. a combination aspherical / linear vertical paraboloid shape. When a suitable such shape is selected, the display screen 210 may be able to be seen as a planar image by the eye 101, such as depicted by virtual image 212 in Figure 7C. By way of contrast, the schematic drawing in Figure 7B illustrates a similar arrangement but with a reflector 230a having an aspherical surface only. In this arrangement, to obtain the same virtual image 212, the display screen 210 must be positioned between the eye 101 and the reflector 230a with the eye 101 1 viewing through an aperture in the reflector 230a. An advantage of the arrangements shown in, for example, Figures 7A and 7C is that the eye 101 does not need to view through the display screen 210 and therefore conventional devices, for example personal electronic communication devices (e.g. smartphones) can be used to provide the display screen 210.

[0141] In addition, achieving a high resolution image and a high frame rate may be assisted by ensuring the eye 101 is sufficiently well illuminated by a dedicated infrared light source, ambient light or a combination thereof. The higher the camera speed, the shorter the exposure time so the more light is required. Also, higher resolution sensors have smaller photo sites for the same size sensor compared to lower resolution sensors, so the more light that is needed to produce a good image. As has been explained, in certain forms, the device 200 comprises at least one light source to illuminate the eye 101 during use of the device.

[0142] 6.2.5. Axial Illumination of the Eye

[0143] As stated earlier, in some forms, the eye tracking device 200 may be configured so that the illumination of the eye 101 is substantially axial with respect to the camera 220, i.e. light 352 from one of the light sources 350 is incident on the eye 101 substantially along the optical axis of the respective camera 220. Figures 2C and 2D are illustrations of exemplary forms of the technology in which such the eye 101 is illuminated in such a manner.

[0144] In these forms, the eye tracking device 200 may comprise a beam splitter 290. The beam splitter 290 may be positioned substantially on or closely proximate the optical axis of the camera 220. The beam splitter 290 may be positioned and oriented to reflect light from light source 350 towards the eye 101. Since the beam splitter 290 is positioned substantially on or closely proximate the optical axis of the camera 220, this makes the light 352 from light source 350 appear to the eye 101 to be coming from the same direction as the camera 220. This enhances the amount of light from light source 350 that is reflected from the fundus of the eye 101, through the pupil 106, back towards the beam splitter 290 and towards camera 220, i.e. enhancing the bright eye effect in the case of light source 350 being a source of infrared light. In addition, it has been found that, even when the direction of gaze of the eye 101 is looking away from the camera 220 at a reasonably large angle, sufficient light may still be reflected back from the eye 101 when the illumination of the eye 101 is sufficiently axial. Reflected light from the eye 101 is incident on the beam splitter 290 and a proportion of the light passes through the beam splitter 290 to the camera 220, so that the camera 220 images the eye.

[0145] In certain forms, for example as shown in Figures 2C and 2D, the beam splitter 290 may be positioned between the camera 220 and the eye 101. Furthermore, the beam splitter 290 may be positioned between the camera 220 and the reflector 230, i.e. the beam splitter 290 may be positioned on an anterior side of the reflector 230.

[0146] Light from the light source 350 reflected by the beam splitter 290 towards the eye 101 may pass through the reflector 230. In some forms, for example as shown in 2C, the reflector 230 may comprise an opening 234, such as described above in relation to Figures 2A, 4 and 7A. Light from light source 350 reflected by beam splitter 290 may pass through the opening 234 to be incident on the eye 101. Light reflected back from eye 101 may also pass through the opening 234 to be captured by the camera 220 for imaging of the eye 101. In other forms, for example as shown in 2D, some or all of the reflector 230 (at least a region of the reflector 230 adjacent to the position of the beam splitter 290, for example a central region) may be semi-transparent so that light from the light source 350 reflected by the beam splitter 290 is able to be transmitted through the reflector 230 to be incident on the eye 101. Light reflected back from eye 101 may also be transmitted through the reflector 230 to be captured by the camera 220 for imaging of the eye 101. One advantage of forms such as shown in Figure 2C compared to forms such as shown in Figure 2D is that reflected light passing from the eye 101 to the camera 220 does not need to be transmitted through the material of reflector 230, which will cause some loss in intensity of the light. Conversely, the opening 234 in the reflector in the form of Figure 2C may result in a blind spot on the display screen 210 (not shown in Figure 2C) from the perspective of the eye 101. However, any disadvantage of this may be mitigated by the nature of what is shown in the display screen 210, e.g. the path 305 of target 303 (described in more detail below) may be selected to avoid the blind spot.

[0147] The forms of the technology shown in Figures 2C and 2D may comprise one or more lenses 209, which may assist in focussing light from the light source 350 reflected by beam splitter 290 onto the eye 101 and / or focussing light reflected back from the eye 101 into the beam splitter 290 for passing on to the camera 220. The lenses 209 may comprise the cylindrical lenses 206 and 207.

[0148] The beam splitter 290 may take any suitable form. For example, the beam splitter 290 may comprise a cube beam splitter or a plate beam splitter. In forms in which the light source 350 is an infrared light source, the beam splitter 290 may be configured to reflect infrared light, for example the coating on a plate beam splitter may be selected accordingly.

[0149] 6.2.6. Frame / Housing

[0150] The eye tracking device 200 is illustrated schematically in Figures 2 to 5 and 7A to 9. In certain forms of the technology, the eye tracking device 200 may additionally comprise a frame 260, exemplified in Figures 8A, 8B and 9, the frame configured to position the other components of the eye tracking device 200 in relation to each other.

[0151] In general terms, the frame 260 may comprise a plurality of structures that each hold in place one of the other components of the eye tracking device 200 in the desired relative position. The plurality of structures may be assembled together as the frame 260. The frame 260 may comprise a reflector retaining structure to position the reflector 230 as described above, a display screen retaining structure to position the display screen 210 relative to the reflector 230 when the reflector is positioned in the reflector retaining structure 264 as described above, a lens retaining structure, a light source retaining structure and / or a camera retaining structure to position the camera(s) 220 / 221 as described above.

[0152] The form of the technology illustrated in Figures 8A and 8B is an example of a device 200 in which the frame 260 may be configured to allow the display screen 210 and at least two linear cameras 220 / 221 to be oriented perpendicularly to each other, i.e. with the linear camera(s) positioned such that their optical axis are substantially perpendicular to a normal to the plane of the display screen 210. In this form, the frame 260 may comprise a display screen retaining structure and a camera retaining structure (not shown) configured to position the display screen 210 and at least two cameras 220 / 221 in the desired orientations. In some forms, the frame 260 may comprise a housing 262 having a camera slot for holding at least two cameras 220 / 221 and a display screen slot for holding the display screen 210, such as described above. In other forms, other suitable mechanisms for positioning the display screen 210 and the cameras 220 / 221 in the described orientations and positions may be used.

[0153] In some forms, for example as shown in Figures 8A and 8B, the device 200 may comprise an eyepiece 271 for assisting a user to position their eye 101 appropriately for looking through the aperture 270 in the housing 262. In addition, the eyepiece 271 may help position each eye that uses the device 200 in a similar position, which may make capturing and analysis of eye tracking data easier, e.g. leading to more consistent / comparable analysis. In the illustrated example, the eyepiece 271 is mounted in front of the illumination unit 354 (i.e. on the side of the illumination unit 354 facing towards the eye 101 during use) in such a way that the eye 101 can gaze through the eyepiece 271, through the illumination unit 354 and through the aperture 270 in the front of the housing 262.

[0154] In some forms the eyepiece may comprise one or more hoods 274, for example a right hood 274a and a left hood 274b. Each hood 274 may be shaped to abut against the region of the patient's face around the eye 101 so that the user can comfortably look into the device 200 while the hood shields ambient light from entering the housing 262 through the aperture 270. In some forms, for example as shown in Figure 8B, the eyepiece 271 may comprise an eyepiece frame 272 to which the one or more hoods 274 are mounted. The eyepiece frame 272 may be formed with one or more apertures in it through which the eye 101 gazes when using device 200. The hoods 274 may be mounted to the eyepiece frame 272 around respective apertures. In some forms, for example as shown in Figure 8B, the eyepiece 271 may comprise an opaque cover 276 to block light passing through one of the apertures in the eyepiece frame 272 and to prevent a user from seeing out of one of the eyes when using the device 200. This may assist with ensuring that the user's vision is only through eye 101 (which gazes into the device 200) when using the device, and may also assist with helping the user know where to position their eyes. In some forms, eyepiece 271 may be able to be disconnected from the housing 262 (or from illumination unit 354, if present) and reconnected in an upside-down orientation. This has the effect of allowing the user's other eye to look into the device 200 and to block the vision of the user's other eye, consequently, allowing movement of the user's other eye to be tracked. Any suitable mechanism to temporarily connect the eyepiece to the rest of the device 200 may be used and, in one exemplary form, an arrangement of magnets / magnetic elements may be used to form a magnetic connection between the eyepiece 271 and the rest of the device 200. The magnets / magnetic elements may be arranged so as to ensure the eyepiece 271 connects in a desired orientation.

[0155] In some forms, the housing 262 may comprise one or more openings in addition to aperture 270 to allow cables to pass through the walls of the housing and connect to one or more of the components inside. The cables may be used for supplying power to electronic devices inside the housing 262 and / or enabling the transfer of data to / from such devices. 6.2.7. Binocular Variant

[0156] The forms of the technology illustrated in Figures 8A and 8B are suitable for tracking the movement of a single eye 101. Single eye movement tracking may be suitable for the assessment of some medical conditions (e.g. concussion) while the assessment of other medical conditions may benefit from tracking the movement of both a patient's eyes simultaneously.

[0157] In certain forms of the technology, an eye tracking device 200 suitable for tracking the movement of two eyes simultaneously may be provided, for example as shown in Figure 9. Such a form may be referred to as a "binocular" or "stereo" variant of the device. In such forms, the device 200 may comprise a single display screen 210 and two reflectors 230, with each reflector 230 positioned to reflect light from the display screen 210 into a respective one of the patient's eyes 101. For example, the two reflectors 230 may be positioned side-by-side inside the housing 262 and be positioned to reflect light from the display screen 210 into a respective one of the eyes 101 so that one eye views the display screen 210 reflected in the first reflector and the other eye views the display screen 210 reflected in the second reflector. In some forms each eye may only be able to see respective parts of the display screen 210 and the display screen 210 may be configured to display two images, which may be positioned side-by-side on the display screen, so that each image is presented to one of the eyes. In some forms, the housing 262 may comprise an internal wall (not shown) to divide the interior volume of the housing 262 into two chambers. The internal wall may be opaque and configured so as to substantially prevent light transmission between the chambers.

[0158] The eye tracking device 200 in this form may further comprise two pairs of linear cameras 224 and 225, with each pair of linear cameras positioned to image a respective eye in two perpendicular axis as the eye looks at the reflector 230. For example, as shown in Figure 9, the linear camera pairs 224 and 225 may be positioned side-by-side on a side of the housing 262 opposing the eye 101 during use, with each linear camera having a view through a respective aperture in the anterior wall 280 of the housing 262. That is, the housing 262 may have for example formed in its anterior wall 280 four apertures, spaced laterally apart for each of two pairs of cameras 224 and 225 to image a respective eye through a respective cylindrical lens and one of the reflectors. In such forms, the device 200 may comprise four camera retaining structures, each positioning one of the linear cameras for imaging a respective eye as described. In alternative forms, reflector 230 may include one or more larger apertures to allow imaging by a number of cameras through a single aperture in the reflector. The eye tracking device 200 in the form of Figure 9, and similar binocular variants, may comprise a housing 262 with two apertures 270 (not shown in Figure 9) in a posterior wall 282 facing towards the user's eyes in use, with each aperture suitably positioned to be viewed through by a respective eye in use, for example the apertures 270 may be laterally spaced apart in the posterior wall 282. Alternatively, the posterior wall 282 may have a single aperture 270 formed in it that is sufficiently large for both eyes to view through. In some forms, an illumination unit 354 such as has been described above may be provided to a front side of the housing 262. In some forms, an eyepiece 271 may be provided to a front side of the housing 262 or illumination unit 354. The eyepiece 271 may comprise a frame 272 and one or more hoods 274 suitable for two eyes to gaze through. For example the frame 272 may have formed therein two apertures, each positioned in front of a respective eye when the device is being used. The device 200 may comprise a single hood 274 configured to abut against a region of the user's face surrounding both eyes during use as shown in Figure 9 so that the user can comfortably look into the device 200 while the hood shields ambient light from entering the housing 262. Alternatively, the device may comprise two such hoods, each configured for abutting against a respective eye during use.

[0159] It should be understood that aspects of the eye tracking devices according to other forms of the technology may apply to the forms of eye tracking device configured to track the movement of two eyes simultaneously. For example, the camera pairs 224, 225 may be configured to view the eye 101 through the reflectors 230 similarly to the manners explained earlier. Other aspects of the earlier forms of the technology may also apply to this two-eye variant of the technology, even if not expressly stated.

[0160] 6.3. Operation of Eye Tracking Device

[0161] In order to use an eye tracking device 200 according to forms of the technology, the reflector 230, display screen 210, cameras 220 / 221, light source 350 and cylindrical lenses 206, 207 are positioned in accordance with the description above. When the eye tracking device 200 is used with display screen 210, eye 101 is positioned so that it views the display screen 210 and the camera 220 is able to image the eye at the same time.

[0162] The display screen 210 may be configured to display any suitable information to the eye 101 to facilitate assessment of eye tracking, for example one or more images, including a moving image. Any suitable image may be displayed and certain forms of the technology are not limited by the nature of the image displayed on the display screen 210. The nature of the image may be dependent on the medical condition that is to be assessed by tracking movement of the eye.

[0163] In one example, as shown in Figures 6A, 6B and 10, the display screen is generally plainly coloured with a target 303 moving around a motion path 305. The target 305 may be any icon, for example a dot. The motion path 305 may be elliptical, circular, sinusoidal, sawtooth or any other motion path considered suitable to test a patient's eye tracking. In the exemplary display screen 210 of Figure 6B, the position of target 303 is shown in successive positions 303a, 303b, 303c, 303d over time along its motion path 305. The same figure also shows projections of that path over time on the X-axis and on the Y-axis. The elliptical motion path 305 of the target 303 in this example may cause the eye to move in both the X direction (corresponding to points 303a and 303c) and the Y direction (corresponding to points 303b and 303d) so as to exercise the eye's range of motion. In some examples, motion path 305 may be altered to be flat or off-axis for some testing regimes. Repeated motion of the target 303 along the motion path 305 smoothly exercises the human eye / brain interface. The movements in the X and Y axis independently are sinusoidal in nature in the example shown, but may be modified to be a sawtooth wave or square wave in other examples. In some forms, the speed and amplitude of the motion of the target 303 on the display screen 210 may be altered over time to increase the cognitive stress and physiological demand on the subject. Increasing the cognitive stress will increase the severity of any symptoms and, by speeding up the motion, a breaking point may be able to be determined. In some forms, the subject may be tested over a set of trials, and the speed of the motion of the target 303 may be progressively increased in each successive trial. In certain forms, the subject may be tested before any injury to establish a baseline performance of the subject (variability in performance is to be expected based on fatigue and other condition of the subject).

[0164] When used within a housing, one advantage of a display screen 210 in which a majority of the screen is evenly illuminated, for example with a light colour such as white, is that the display screen 210 provides a relatively large diffuse source of illumination within the internal chamber of the housing 262 that illuminates the eye 101 for the camera 220 to capture images of the eye. This may enable adequate illumination to be achieved with relatively low levels of illumination per pixel on the display screen 210 because a large number of pixels on the display screen 210 are illuminated at the relatively low level, so the overall illumination may be sufficiently high. When used in conjunction with an infrared light source, the illumination from the display screen may be altered to ensure the bright eye effect generated by the IR light source is not compromised, while still enabling the display screen to be visually clear to the user. The display screen 210 may be controlled to present information to the patient, for example a fixed or moving target for the patient to gaze at during eye tracking, by a processor. The processor may be configured to generate data representative of the position of the target 303. Suitable movement protocols may be provided to the processor, for example from a memory or via a suitable communication link. In some forms, the processor may be the same processor as the processor 404 that is comprised as part of the data analysis system 400. In other forms, the processor controlling the display screen 210 may be a different processor from processor 404.

[0165] In certain exemplary uses of the eye tracking device 200, the patient is asked to look at the target 305 and follow its movement with their gaze as it moves around display screen 210. The camera 220 captures information on how the eye 101 moves in response to this stimulus.

[0166] The eye tracking device 200 may be used to track the movement of one of the patient's eyes at a time. The eye to be assessed can be positioned suitably with respect to the eye tracking device 200 and, when the other eye is to be assessed, the other eye can be brought into position.

[0167] In operation of another form of the technology, for example a device 200 such as shown in Figure 9 that may be referred to as a binocular version, although the device 200 may be configured for two eyes to be presented to the device at a time, eye tracking may only occur for one eye at a time. For example, the display screen 210 may be configured to initially display an image for eye tracking in a part of the screen that is visible by the first eye, and the respective pair of cameras capture image data of movement of the first eye. Subsequently, the display screen 210 may be configured to display an image for eye tracking in a part of the screen that is visible by the second eye, and the respective pair of cameras at each eye capture image data of movement of the second eye. One advantage of using a binocular version to test eyes in this manner compared to using a monocular version on each eye is that the user does not have to change the position of the device when changing from tracking one eye to the other.

[0168] 6.4. Method of Analysing Data to Determine Position of Pupil and to Track Eye Movement

[0169] There will now be described exemplary methods of analysing the data generated by operation of an eye tracking device 200 according to certain forms of the technology. Unless otherwise stated, the steps of the exemplary methods described here are carried out by processor 404 of the data analysis system 400. The processor 404 may receive data from the eye tracking device 200 via a suitable communications link, for example network 416.

[0170] Determining the direction of gaze of the eye based on image data values generated may be achieved by determining the position of a pupil in an eye along two directions, which may be two mutually perpendicular directions, for example along a horizontal X-axis and a vertical Y-axis, at a single point in time. By determining the position of the pupil multiple times across a time period, the movement of the eye over this period of time can be tracked.

[0171] This method is generally illustrated in Figure 12, which shows a two-dimensional image 500 of an eye. The image 500 illustrates the field of view of the camera 220 or cameras 220 and 221 of eye tracking device 200 according to certain forms of the technology. If the camera 220 is configured to capture a two-dimensional image, the image 500 may be an image captured by this camera. If the eye tracking device 200 comprises two linear cameras 220 and 221, the image 500 may be representative of the field of view of both cameras in combination, i.e. the region from which the two cameras capture light. In Figure 12, image 500 is shown as an infrared image of the eye, with the eye pupil 106 reflecting infrared light to produce the bright eye effect, making its position clear to identify.

[0172] The field of view represented by image 500 in Figure 12 may be considered as being comprised of a plurality of slices in one or more directions, for example a plurality of columns extending in the Y direction indicated in Figure 12, and a plurality of rows extending in the X direction indicated in Figure 12. In the image 500, these columns and rows are made up of pixels but in the field of view captured in the image 500, these columns and rows are regions of space.

[0173] An eye tracking system 300 that determines the position of the pupil 106 of the eye according to certain forms of the technology may operate by totalling the intensity of light in each of the slices (e.g. rows and columns) and analysing the resultant intensities.

[0174] In forms of the technology in which eye tracking device 200 comprises two linear cameras 220 and 221, the totalling of the intensity of light in each of the slices (e.g. rows and columns) may be achieved by the cylindrical lenses 206 and 207 associated with each of the cameras. The first cylindrical lens 206 is oriented in one direction, for example perpendicular to the transverse plane of the eye (vertically) between the eye and a corresponding linear camera oriented in the same direction. Infrared light reflected off the eye is focussed by the cylindrical lens onto the sensor of the corresponding linear camera and the effect of this is that all light in the same horizontal row within the field of view of the camera (together with the lens) is focussed onto the pixel sensor of the camera corresponding to that horizontal row. This results in the vertically oriented linear camera generating a set of image data values where each value in the set is representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view. The line 510 shows an exemplary set of such values in the case of image 500. Line 510 plots the total intensity of each row against the vertical position of each respective row in the image 500.

[0175] Similarly, the second cylindrical lens 207 is oriented in a different direction, for example perpendicular to the sagittal plane of the eye (horizontally) between the eye and a corresponding linear camera oriented in the same direction. Infrared light reflected off the eye is focussed by the cylindrical lens onto the sensor of the corresponding linear camera and the effect of this is that all light in the same vertical column within the field of view of the camera (together with the lens) is focussed onto the pixel sensor of the camera corresponding to that vertical column. This results in the horizontally oriented linear camera generating a set of image data values where each value in the set is representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view. The line 520 shows an exemplary set of such values in the case of image 500. Line 520 plots the total intensity of each column against the horizontal position of each respective column in the image 500.

[0176] Consequently, in these forms, one of the linear cameras may be considered to be an image data generator that generates a set of image data values representative of the total intensity of light in one direction in the field of view, and the other linear camera may be considered to be an image data generator that generates a set of image data values representative of the total intensity of light in another direction in the field of view.

[0177] In other forms, the eye tracking device 200 may comprise a single camera 200 configured to capture a 2D image of the field of view, which may include the eye 101, for example image 500 shown in Figure 12. The 2D image 500 is a 2D array of pixels, the pixels configured in a plurality of parallel columns along the X-axis, and a plurality of parallel rows across the Y-axis, each pixel having a value indicative of the light intensity corresponding to that pixel in the image. The rows and columns of the image 500 are sets of image data values. In certain forms, the totalling of the intensities of light in each of the rows and columns of the field of view may be achieved by independently totalling the values of pixel light intensities in each row and column of the image 500. The totalling may be achieved by processor 404 summing the intensities of the light intensities for the pixels in each row / columns. Any suitable summing function may be used, for example a simple sum, a weighted sum, etc. In these forms, the processor 404 may be considered to act as an image data generator of a first set of image data values when summing the intensities of rows of image 500, and to act as an image data generator of a second set of image data values when summing the intensities of columns of image 500.

[0178] It will be appreciated that the outcome of both approaches described above may be the same, i.e. a set of image data values representative of the total intensity of light from columns within the field of view, and a set of image data values representative of the total intensity of light from rows within the field of view. In one approach, the cylindrical lenses act as the summation mechanism, while in the other approach the processor 404 acts to sum the intensities.

[0179] Plots of the image data values along each of the X and Y axes are shown as lines 510 and 520 in Figure 12. Each line may comprise one or more peaks 150 and / or troughs 151 indicating regions of high or low light intensity in the field of view. The position of a pupil of a human eye in a direction perpendicular to the orientation of the slices may be able to be identified by analysing the light intensities in the relevant directions, for example by analysing the positions of the peaks and troughs. For example, a pupil subject to the "bright eye" effect when subject to infrared illumination will display as an area of bright illumination, surrounded by a dark region representing the iris of the eye. The contrast between the illuminated pupil and the surrounding iris, which absorbs rather than reflects IR light, is identifiable in the resulting plotted lines for each axis by two troughs indicating low light levels positioned either side of a peak indicating comparatively higher light levels. The processor 404 may be configured to execute peak and / or valley identification algorithms in order to detect the position of these features in the data, and consequently determine the position of the pupil in each axis. Using the pupil position information from each one-dimensional axis, a two-dimensional pupil position can be determined for that point in time and represented as a pupil position value.

[0180] To track the position of the eye over time, multiple images may be taken over a time period and the image data may be analysed using the method above to determine a pupil position value at multiples instances over the period of time. In some forms, changes in the pupil position values over the period of time may be identified and the movement of the eye may be tracked based on the changes over time. The processor may be configured to generate data representative of the position of the pupil and / or the movement of the eye 101 from the image data. The processor may further be configured to output the data representative of the movement of the eye 101. The data may be output by the processor by sending the information over a suitable communication network or by outputting the information via an output device, for example a user interface such as display device 414. Alternatively, the information may be stored in a memory, for example a memory of portable electronic device, for later output. The outputted data representative of the movement of the eye 101 may be an array of data representing the position and / or movement of the eye 101, for example the pupil 106, at a plurality of times. The data may be outputted in any suitable format, for example a CSV file.

[0181] The processor may further be configured to output data representative of the position of the target 303 (which may include data representative of movement of the target 303 if the target is moving). This data may be contemporaneous to the data representative of the movement of the eye 101, i.e. such that the target data represents movement of the target 303 when the eye 101 is gazing at it and the eye's movement is captured in the eye movement data. The data may be output by the processor by sending the information over a suitable communication network or by outputting the information via an output device, for example a user interface such as display device 414. Alternatively, the information may be stored in a memory, for example a memory of portable electronic device 250, for later output. The outputted data representative of the movement of the target 303 may be an array of data representing the position and / or movement of the target 303, at a plurality of times. The data may be outputted in any suitable format, for example a CSV file.

[0182] In some forms, the processor may output the data representative of the movement of the eye 101 and the data representative of the movement of the target 303 together, for example in the same data file. The outputted data may be time-stamped so that the position of the eye 101 is recorded relative to the position of the target 303 at each time point.

[0183] The methods, systems and devices of the present invention may allow for effective eye tracking to be achieved with a significant reduction in processing power. Traditional 2D cameras generate significant amounts of data and therefore a high level of computational processing is required to analyse the image data to determine the position of an eye. This may also result in the need for significant thermal management. This becomes challenging in small scale, portable devices that are preferred for use in situations where time sensitive eye tracking analysis is required. In forms of the technology that use linear cameras in combination with cylindrical lenses as described above, a significant reduction in processing power may be provided. For example, the use of two 2000 pixel linear cameras results in the analysis being performed on 4000 pixel values, which at an image capture rate of 2000 frames per second requires 8 megapixels of processing power. In comparison, a traditional 2D camera capturing an image of 2000 x 2000 pixels operating at 2000 frames per second requires 8 gigapixels of processing capability. As a result of this, such systems can incorporate lower cost, battery-operated processors, reducing manufacturing costs, and increasing the portability of the devices.

[0184] In forms that capture 2D images of the eye and the totalling of the intensities of the pixel values in the image in two different directions is performed by a processor, it is necessary to transfer all the image data of a 2D image (which, in the case, of a 2000 x 2000 pixel image is 4 million values), which is the same as the traditional image analysis example, but the data analysis is only performed on 4000 pixel values, which again permits faster processing. One benefit of these forms is that the optical arrangement of the camera and any lenses is simpler than the linear camera versions.

[0185] It has been described that, in some forms of the technology, the eye tracking device 200 may comprise an additional camera 222 that captures two-dimensional visual images of the eye 101 while the linear cameras 220 and 221 are also capturing images of the eye 101. In such forms, the data analysis system 400 may be configured to perform a dot detection algorithm, for example a dot centroid detection algorithm, on the captured image data in order to detect the bright spot indicative of the position of the pupil 106 because of the bright eye effect caused by reflection of infrared light through the pupil 106. The dot detection algorithm may be used to ascertain the position of the pupil 106 in an image and consequently to track movement of the eye over time. This may be helpful as a secondary mechanism for detecting the position of the pupil and / or tracking the movement of the eye over time.

[0186] 6.5. Use of Eye Tracking Information

[0187] Through use of the eye tracking device 200, information on the movement of the eye 101 in response to changing images on the first display screen 210, for example, movement of the target 305, may be captured. This information may be displayed on the second display screen 211, stored on a memory of one or more cameras, transmitted to another device, or any combination of these options. The information, if transmitted to another device, for example to a remote device, may be stored at the other device and / or displayed on a display screen.

[0188] Certain forms of the present technology are not limited by the type of information on movement of the eye 101 that is obtained through use of eye tracking device 200.

[0189] Based on the information of the movement of the eye, one or more medical conditions may be examined assessed and / or diagnosed. Certain forms of the present technology are not limited by the nature of the assessment or the medical condition(s).

[0190] 6.6. Other Remarks

[0191] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of "including, but not limited to".

[0192] The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference.

[0193] Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.

[0194] The technology may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

[0195] Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

[0196] It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the technology and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present technology.

Claims

7. CLAIMS1. A device for tracking movement of an eye, the device comprising: one or more light sources for illuminating the eye; a first cylindrical lens and a first linear camera for imaging the eye, wherein the first cylindrical lens and the first linear camera are positioned so that the first linear camera images the eye through the first cylindrical lens, the first cylindrical lens being oriented substantially parallel to the first linear camera; and a second cylindrical lens and a second linear camera for imaging the eye, wherein the second cylindrical lens and the second linear camera are positioned so that the second linear camera images the eye through the second cylindrical lens, the second cylindrical lens being oriented substantially parallel to the second linear camera, wherein the first cylindrical lens and the first linear camera are oriented substantially non-parallel to the second cylindrical lens and the second linear camera.

2. A device as claimed in claim 1, wherein the first linear camera and the first cylindrical lens are oriented substantially perpendicular to the second linear camera and the second cylindrical lens.

3. A device as claimed in claim 2, wherein the device is configured so that, in use, the first linear camera and the first cylindrical lens are oriented perpendicular to the transverse (or horizontal) plane of the eye, and the second linear camera and the second cylindrical lens are oriented perpendicular to the sagittal plane (vertical) of the eye.

4. A device as claimed in any one of claims 1 to 3, wherein the first and second linear cameras are infrared-sensitive linear cameras and the one or more light sources comprises an infrared light source.

5. A device as claimed in claim 4, wherein the one or more light sources comprises two infrared light sources associated with each linear camera, wherein one of the infrared light sources is positioned either side of each linear camera.

6. A device as claimed in claim 4, wherein the eye tracking device is configured so that light from one of the light sources is incident on the eye substantially along the optical axis of a respective one of the linear cameras.

7. A device as claimed in any one of claims 1 to 6, wherein the device comprises a display screen positioned such that, in use, the eye can view the display screen.

8. A device as claimed in claim 7, wherein the display screen is comprised as part of a first portable electronic device.

9. A device as claimed in any one of claims 7 to 8, wherein the device comprises a reflector and the display screen is positioned relative to the reflector such that, in use, the eye views the display screen reflected in the reflector.

10. A device as claimed in claim 9, wherein at least one of the linear cameras is positioned to image the eye through the reflector.

11. A device as claimed in claim 10, wherein the reflector comprises an opening and at least one of the linear cameras is positioned to image the eye through the opening in use.

12. A device as claimed in claim 10, wherein the reflector is semi-transparent and the device is configured so that at least one of the linear cameras is able to image the eye through the reflector.

13. A device as claimed in any one of claims 9 to 12, wherein the reflector has a reflective side and the reflective side is concave in at least one plane.

14. A device as claimed in any one of claims 1 to 13, wherein the device is configured such that the eye substantially fills the field of view of each linear camera.

15. A device as claimed in any one of claims 1 to 14, wherein the device includes a housing adapted to provide a light-controlled environment.

16. A processor-implemented method for determining the position of a pupil of an eye within a field of view of a camera, the method comprising;receiving a first set of image data values, each value in the set representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view; receiving a second set of image data values, each value in the set representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view; and analysing the first and second set of image data values to determine the position of the pupil.

17. A processor-implemented method for tracking the movement of an eye within a field of view of a camera, the method comprising: a) receiving a first set of image data values, each value in the set representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view; b) receiving a second set of image data values, each value in the set representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view; c) analysing the first and second set of image data values to determine a position of the pupil at a first time; d) repeating steps a) - c) at each of a plurality of times over a period of time to generate a set of pupil positions over the period of time; and e) analysing the set of pupil positions generated at step d) to track the movement of the eye.

18. A method as claimed in any one of claims 16 to 17, wherein the first and second set of image data values received are representative of a two dimensional image of the field of view, each value in the first set of image data values generated from a sum of light intensities in a column of the two dimensional image and each value in the second set of image data values generated from a sum of light intensities in a row of the two dimensional image.

19. A method as claimed in any one of claims 16 to 18, wherein the step of analysing the first and second set of image data values to determine the position of the pupil comprises determining a location of one or more peaks and / or troughs in the first and second sets of image data values.

20. A method as claimed in any one of claims 16 to 19, wherein the step of analysing the set of pupil position values to track movement of the eye comprises identifying changes in the pupil position values over the period of time and tracking the movement of the eye based on the changes over time.

21. A method as claimed in any one of claims 16 to 20, wherein the method comprises the further step of providing data representing the tracking of the eye movement to a user interface for display to a user.

22. A system for determining the position of a pupil of an eye within a field of view of a camera, the system comprising: a first image data generator for generating a first set of image data values, each value in the set representative of the total intensity of light from a respective column of a plurality of parallel columns within the field of view; a second image data generator for generating a second set of image data values, each value in the set representative of the total intensity of light from a respective row of a plurality of parallel rows within the field of view; and a processor for analysing the first and second sets of image data values to determine a position of the pupil.

23. A system as claimed in claim 22, wherein the first and second image data generators are configured to generate image data values at each of a plurality of times over a period of time to generate a set of pupil position values over time, and wherein the processor is configured to analyse the set of pupil positions over the period of time to track the movement of an eye.

24. A system as claimed in any one of claims 22 to 23, wherein the system further includes a user interface for displaying data representing the eye tracking movement.

25. A system as claimed in any one of claims 22 to 24, wherein the first and second image data generators comprise two linear cameras oriented substantially non-parallel to each other.

26. A system as claimed in claim 25, wherein the two linear cameras are oriented substantially perpendicular to each other.

27. A system as claimed in any one of claims 22 to 24, wherein the processor comprises the first and second image data generators, wherein the first and second set of image data values received are representative of a two dimensional image of the field of view, each value in the first set of image data values generated from a sum of light intensities in a column of the two dimensional image and each value in the second set of image data values generated from a sum of light intensities in a row of the two dimensional image.

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