Positioning systems for ophthalmic instruments

Abstract

A space-compact, lightweight positioning system for guiding an operator to position an ophthalmic instrument relative to an eye of a test subject has first and second light sources and an area detector spaced apart from a measurement axis of the instrument and from each other for providing a positioning image that can be evaluated relative to stored calibration image information to determine a current position of the instrument relative to the eye. The first and second light sources can be mounted within a lateral distance of less than or equal to 25 mm. First and second illumination axes associated with the light sources can be located in a horizontal plane containing the measurement axis, and an observation axis of the area detector can be located in a vertical plane containing the measurement axis. The light sources and the area detector can intersect a plane normal to the measurement axis.

Description

Technical Field

[0001] The present disclosure relates to ophthalmic instruments that are positioned by an operator relative to a test subject's eye as a prerequisite for measuring ophthalmic parameters of the eye. For example, the present invention relates to rebound tonometers, which measure intraocular pressure (IOP) by contacting the cornea of ​​the eye with a disposable probe, and non-contact tonometers, which measure IOP by temporarily deforming the cornea using air pulses. Background Art

[0002] A rebound tonometer is an ophthalmic instrument that advances a movable measuring probe toward the cornea of ​​the eye along a measuring axis in a controlled manner to measure intraocular pressure. During measurement, the probe contacts the cornea, decelerates at a rate that depends on the intraocular pressure, and then rebounds back to the instrument housing in a direction away from the cornea. The rebound tonometer detects the movement of the measuring probe and determines the intraocular pressure based on the detected movement of the probe. For example, the measuring probe may have a magnetized axis that travels within a coil in the instrument housing. The coil may be energized momentarily to push the probe toward the cornea by electromagnetic force, and then, after the energizing current of the coil is cut off, a current is generated in the coil by moving the probe to provide a detectable voltage signal that represents the probe speed that varies with time. Alternatively, two coils may be provided, one of which is used to advance the probe, and the moving probe generates a current in the other coil to provide a measurement voltage signal. The voltage signal may be recorded and processed to determine the measured IOP value.

[0003] Proper three-dimensional positioning of the rebound tonometer relative to the eye is an important factor in the accuracy and repeatability of IOP measurements. Before advancing the probe to start IOP measurement, the rebound tonometer is ideally positioned by the operator so that the measurement axis intersects the corneal vertex when the test subject gazes directly along the measurement axis (XY alignment), and the rounded tip of the measurement probe is located at a predetermined working distance (Z distance) from the corneal surface. Although it is not possible to achieve ideal three-dimensional positioning due to movement of the operator's hand holding the tonometer and / or movement of the test subject, three-dimensional positioning within an acceptable tolerance relative to the ideal position is required to obtain reliable measurements.

[0004] A non-contact tonometer, also known as an air puff tonometer, is another type of ophthalmic instrument used to measure IOP. Similar to the rebound tonometer, the non-contact tonometer may be hand-held and manually positioned by the operator. The non-contact tonometer has three-dimensional positioning requirements similar to the above-mentioned rebound tonometer, except that the fluid release tube used to release the air pulse toward the eye defines the measurement axis and working distance.

[0005] Known systems for guiding an operator to position an ophthalmic instrument relative to a test subject's eye tend to be bulky and complex. As a result, the measuring head of the instrument is correspondingly large and obstructs the operator's direct line of sight to the test subject's face, making the instrument more difficult to position and increasing the risk that the operator may inadvertently contact the test subject's face or eye with the instrument. In addition to its large size, the measuring head can be undesirably heavy. If the ophthalmic instrument is handheld, this makes it more difficult for the operator to hold the ophthalmic instrument steady and in place while taking measurements.

[0006] There is a need for a spatially compact positioning system for an ophthalmic instrument, thereby reducing obstruction of a direct line of sight from an operator to a patient's face. There is also a need for a lightweight positioning system for a handheld ophthalmic instrument, so that the measuring head of the instrument is not overweight. Summary of the invention

[0007] The present disclosure provides a compact, lightweight positioning system for guiding an operator to position an ophthalmic instrument relative to an eye of a test subject. The ophthalmic instrument may be, for example, a rebound tonometer that advances a probe toward the eye along a measurement axis of the instrument, or a non-contact tonometer that releases a fluid pulse toward the eye along a measurement axis of the instrument.

[0008] An ophthalmic instrument in combination with a positioning system generally includes a first light source and a second light source, an area detector, a signal processing electronic device, a memory, and an image evaluation module. The first light source and the second light source and the area detector are each spaced apart from a measurement axis of the ophthalmic instrument and from each other. The first light source and the second light source direct corresponding illumination beams to the eye along a first illumination axis and a second illumination axis, and when the ophthalmic instrument is positioned near the eye in preparation for measurement, the area detector captures a positioning image of the eye. Each positioning image includes a first source image corresponding to the first light source and a second source image corresponding to the second light source. The signal processing electronic device is connected to the area detector for receiving a plurality of pixel signals representing the positioning image and converting the plurality of pixel signals into a digital positioning image.

[0009] The memory stores positioning calibration information corresponding to an ideal three-dimensional position of the ophthalmic instrument relative to the calibration eye, wherein the positioning calibration information is based on a calibration position of a first source image and a calibration position of a second source image in a calibration image captured by the area detector when the ophthalmic instrument is at the ideal three-dimensional position relative to the calibration eye.

[0010] The image evaluation module is configured to evaluate each digital scout image to determine current positioning information corresponding to a current three-dimensional position of the ophthalmic instrument relative to the eye, wherein the current positioning information is based on a current position of the first source image and a current position of the second source image in the digital scout image. The image evaluation module is further configured to compare the current positioning information with positioning calibration information stored in the memory and calculate a position difference representing a difference between the current three-dimensional position of the ophthalmic instrument relative to the eye and an ideal three-dimensional position of the ophthalmic instrument relative to the calibration eye.

[0011] The ophthalmic instrument may further include a display connected to the image evaluation module, and the image evaluation module may be further configured to generate a localization icon representing the current three-dimensional position of the ophthalmic instrument relative to the eye, and output the digital localization image and the localization icon to the display, wherein the digital localization image and the localization icon are superimposed to provide a localization guide image displayed on the display. The localization icon may be scaled so that the size of the localization icon is inversely proportional to the current working distance of the ophthalmic instrument from the eye along the measurement axis, and the appearance attributes (e.g., color) of the localization icon may depend on whether the calculated position difference is within a predetermined localization tolerance for measurement purposes.

[0012] The ophthalmic instrument may further include a controller for initiating the measurement. The image evaluation module may be connected to the controller and may be further configured to send a position confirmation signal to the controller when the calculated position difference is within a predetermined positioning tolerance, and when the ophthalmic instrument is in an automatic measurement mode, the controller may automatically initiate the measurement in response to the position confirmation signal.

[0013] In the disclosed embodiments, the first light source and the second light source may be assembled within a lateral distance of less than or equal to 25 mm. The first illumination axis and the second illumination axis may be coplanar with the measurement axis and form an angle bisected by the measurement axis. The observation axis of the area detector may be coplanar with the measurement axis. The first illumination axis and the second illumination axis may be arranged in a horizontal plane containing the measurement axis, and the observation axis may be arranged in a vertical plane containing the measurement axis. The first illumination axis and the second illumination axis may converge at a first point along the measurement axis within the field of view of the area detector, and the observation axis may intersect the measurement axis at a second point spaced from the first point along the measurement axis. The ophthalmic instrument may have a working distance reference point on the measurement axis, wherein the distance between the working distance reference point and the second point is greater than the distance between the working distance reference point and the first point. The first light source, the second light source, and the area detector may intersect a plane normal to the measurement axis of the ophthalmic instrument. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken in conjunction with the accompanying drawings, in which:

[0015] Figure 1 is a perspective view of an ophthalmic instrument formed according to an embodiment of the present disclosure;

[0016] Figure 2 yes Figure 1 Another perspective view of the ophthalmic instrument shown;

[0017] Figure 3 is a front view of a measuring portion of an ophthalmic instrument with a cover removed to illustrate components of a positioning system of the ophthalmic instrument;

[0018] Figure 4 is another view of a measuring portion of an ophthalmic instrument with a cover removed to illustrate components of a positioning system of the ophthalmic instrument;

[0019] Figure 5 It is roughly along Figure 3 A cross-sectional view of a measuring portion of an ophthalmic instrument taken along line VV in FIG.

[0020] Figure 6 is a schematic top view showing components of a positioning system in relation to an eye of a test subject;

[0021] Figure 7 is a schematic side view showing components of a positioning system in relation to an eye of a test subject;

[0022] Figure 8 is a schematic diagram of a regional detector of a positioning system;

[0023] Fig. 9 is a schematic electronic block diagram of an ophthalmic instrument;

[0024] Fig.10 is an example of a calibration image captured by the area detector of the positioning system;

[0025] Fig.11A , Fig. 11B and Fig. 11C An example of a positioning guide image generated by a positioning system and displayed to an operator is shown, wherein the positioning guide image represents a positioning image captured by an area detector of the positioning system together with a positioning target and a positioning icon;

[0026] 12 is a flow chart illustrating the operation of the positioning system in a manual measurement mode of the ophthalmic instrument; and

[0027] 13 is a flow chart illustrating the operation of the positioning system in the automatic measurement mode of the ophthalmic instrument. DETAILED DESCRIPTION

[0028] Figures 1 to 5An ophthalmic instrument 10 for measuring ophthalmic parameters of an eye according to an embodiment of the present disclosure is shown. In the figure, the ophthalmic instrument 10 is implemented as a rebound tonometer for measuring IOP, however it should be understood that the ophthalmic instrument 10 can be implemented as a non-contact tonometer for measuring IOP, or can be implemented as another type of ophthalmic instrument for measuring parameters of the eye other than IOP. The ophthalmic instrument 10 includes a measurement axis 11, which, within the scope of the rebound tonometer shown, is the axis along which the measuring probe 12 is advanced toward the eye of the test subject. Within the scope of a non-contact tonometer (not shown), the measurement axis 11 is the axis of a fluid release tube, through which a fluid pulse (e.g., an air puff) is directed to the eye of the test subject.

[0029] The ophthalmic instrument 10 may have a housing 14 defining a handle portion 16 and a measuring head 18 at the top of the handle portion 16. A measuring button 20 may be provided on the handle portion 16. When the ophthalmic instrument 10 is in a manual operation mode, the measuring button 20 is depressible by the operator to trigger a measurement of the ophthalmic instrument 10. In the illustrated embodiment, the measuring probe 12 has a magnetizing axis 12A coaxially received in a front coil 15 and a rear coil 16 disposed in a tubular barrel 17A within the measuring head 18 of the housing 14. The front coil 15 may be momentarily energized to propel the probe 12 toward the cornea by electromagnetic force. The rear coil 16 may be used as a sensing coil for sensing the motion of the probe 12, wherein a current is generated in the rear coil 16 to provide a detectable voltage signal representing the probe velocity over time. The voltage signal may be recorded and processed in a known manner to determine the measured IOP value.

[0030] Now also refer to Figures 6 to 8 , the ophthalmic instrument 10 includes a positioning system including a first light source 30A spaced from the measurement axis 11 and arranged to direct a first illumination beam along a first illumination axis 32A, and a second light source 30B spaced from the measurement axis 11 and arranged to direct a second illumination beam along a second illumination axis 32B. The positioning system also includes an area detector 40 spaced from the measurement axis 11 and from the first light source 30A and the second light source 30B. The area detector 40 has an observation axis 42 extending normal to a detection plane 44 of the area detector, in which a two-dimensional array of light-sensitive pixels 46 is arranged. The first illumination axis 32A, the second illumination axis 32B and the observation axis 42 extend through a light-transmitting window 22 surrounding a probe base cap 17B at the front of the measurement head 18. As will be described in more detail below, the area detector 40 is constructed and arranged to continuously capture a positioning image of the eye when the ophthalmic instrument 10 is positioned near the eye in preparation for measurement.

[0031] As a non-limiting example, each of the first and second light sources 30A, 30B can be a light emitting diode (LED) that emits red diffuse light. Using a red LED is advantageous because it allows the positioning system to distinguish between light associated with the positioning system and all other colors detected by the area detector 40, and because it allows the test subject to use the red illuminated LED as a fixation target during measurement. For example, the test subject can be instructed to fixate at the midpoint between the two red LEDs so that the measurement axis 11 is normal to the corneal surface. Also as a non-limiting example, the area detector 40 can be a CameraCubeChip available from OmniVision, Inc. of Santa Clara, California, with part number OVM7692-RYAA. TM A 640×480 color pixel image sensing array is provided as part of the

[0032] Figures 3 to 7 A possible implementation of the positioning system is shown, in which the area detector 40 is mounted on a circuit board 45, and the light sources 30A, 30B are mounted on corresponding branches of a bifurcated flexible connector 47 extending from the circuit board 45. Figure 7 , the circuit board 45 may be tilted relative to the measurement axis 11 such that the observation axis 42 of the area detector 40 forms an elevation angle θE with the measurement axis 11. The circuit board 45 may include an opening 49 through which the barrel 17A may extend. In the illustrated embodiment, the first illumination axis 32A and the second illumination axis 32B are coplanar with the measurement axis 11 in a horizontal plane and form an angle θAB that is bisected by the measurement axis 11. According to the illustrated embodiment, the observation axis 42 may be coplanar with the measurement axis 11 in a vertical plane. The first illumination axis 32A and the second illumination axis 32B may converge at a first point P1 along the measurement axis 11 within the field of view of the area detector 40, and the observation axis 42 may intersect the measurement axis 11 at a second point P2 spaced apart from the first point P1 along the measurement axis 11. The ophthalmic instrument 10 may also include a working distance reference point P3 on the measurement axis 11, wherein a working distance WD of the instrument 10 relative to the eye is defined as the distance between the reference point P3 and the corneal surface of the eye. For example, where the ophthalmic instrument 10 is a rebound tonometer, the working distance reference point P3 may be a point at the front tip of the measuring probe 12, and where the ophthalmic instrument 10 is a non-contact tonometer, the working distance reference point P3 may be a point at the front tip of the fluid release tube of the tonometer. In the illustrated embodiment, the distance between the reference point P3 and the second point P2 is greater than the distance between the reference point P3 and the first point P1. Figure 6 and Figure 7As best understood in FIG. 1 , the first light source 30A, the second light source 30B and the area detector 40 may be arranged such that they intersect a plane 41 that is normal to the measurement axis 11 .

[0033] With respect to the illustrated embodiment, the following dimensions may be used in practice, however, these dimensions are provided as examples only and it should be understood that other dimensions may be used in practice: working distance WD = 6.00 mm; illumination axis angle θAB = 53.6°; observation axis elevation angle θE = 21.8°; illumination distance D1 = 20.012 mm (for both light sources 30A and 30B); observation distance D2 = 23.07 mm.

[0034] Fig. 9 is a schematic electrical block diagram of an ophthalmic instrument 10, which includes a signal processing electronic device 60 connected to the area detector 40 for receiving a plurality of pixel signals and converting the plurality of pixel signals into a digital positioning image. For example, the signal processing electronic device 60 can be provided by a CameraCubeChip as described above. TM The on-board signal processing electronics provided as part of the system include an analog-to-digital converter, a digital signal processor and a formatter, and an image output interface.

[0035] The ophthalmic instrument 10 also includes a memory 70 that stores positioning calibration information. For example, the memory 70 can be implemented as a non-volatile memory that retains the stored information when the power to the ophthalmic instrument 10 is cut off. The memory 70 can be a ferroelectric random access memory (F-RAM) module or another type of memory. An example of a suitable F-RAM module can be obtained from Cypress Semiconductor Corporation under the part number FM24V10GTR.

[0036] The ophthalmic instrument 10 includes a microcontroller 80 that is programmed by software instructions stored in a memory to control various operating functions of the ophthalmic instrument 10. As a non-limiting example, the microcontroller 80 may be implemented as a microcontroller available from STMicroelectronics with part number STM32L4R9AII6, which has - M4 core as central processing unit (CPU) and embedded flash memory. Alternatively, the microcontroller 80 may be implemented as another type of controller configured to control the operational functions of the ophthalmic instrument 10 .

[0037] The ophthalmic instrument 10 also includes an image evaluation module 82 configured by stored software instructions to evaluate the digital localizer image output from the signal processing electronics 60 with reference to the localizer calibration information stored in the memory 70 and calculate a position difference representing the difference between the current three-dimensional position of the ophthalmic instrument 10 relative to the eye and the ideal three-dimensional position of the ophthalmic instrument 10 relative to the eye. Fig. 9 As shown, the image evaluation module 82 may be incorporated into the microcontroller 80. Alternatively, the image evaluation module 82 may be implemented by a separate computing circuit module connected to the microcontroller 80.

[0038] The ophthalmic instrument 10 also includes a display 84 connected to the microcontroller 80 for presenting information to an operator. For example, the display 84 can be used to display measurement results and other measurement data to the operator. The display 84 can also be used to present a positioning guide image to the operator to help guide the operator to position the ophthalmic instrument 10 relative to the eye of the test subject to perform measurements as described in more detail below. As a non-limiting example, the display 84 can be a liquid crystal display (LCD).

[0039] The ophthalmic instrument 10 may also include menu navigation / selection buttons 86 that are connected to the microcontroller 80 and enable an operator to set operating parameters of the ophthalmic instrument 10 in conjunction with an operating system menu displayed on the display 84. The ophthalmic instrument 10 may also include an audio speaker 88 connected to the microcontroller 80.

[0040] In one aspect of the present disclosure, the first light source 30A and the second light source 30B can be assembled within a lateral distance LD of less than or equal to 25 mm (about one inch). This lateral distance limitation is critical in several important aspects. First, it enables the lateral width of the measuring head 18 to be limited to approximately 37 mm (some lateral space on both sides of the light sources 30A, 30B is required for the housing structure and hardware to install the internal components in the measuring head 18). This is important because it helps prevent the sides of the measuring head 18 from contacting the nose of the test subject when the measuring axis 11 is positioned in front of the eye for measurement. As shown in the accompanying drawings, the measuring axis 11 can be positioned in the middle between the sides of the measuring head 18 so that the distance from each side of the measuring head 18 to the measuring axis 11 is no greater than about 19 mm. The lateral distance from the center of each pupil to the corresponding proximal side of the nose is slightly less than half of the interpupillary distance. Since the interpupillary distance of adults is generally in the range of about 54 mm-74 mm, the distance from the pupil to the nose is generally in the range of about 23 mm-32 mm. Therefore, by fitting the light sources 30A, 30B within a lateral distance LD of 25 mm, thereby limiting the lateral distance from the measurement axis 11 to each side surface of the measurement head to approximately 19 mm, some clearance is maintained between the sides of the measurement head 18 and the bridge of the test subject's nose during measurement.

[0041] Limiting the lateral distance LD to 25 mm is critical in a second respect, as it provides the operator with direct view of the eye being measured, in addition to direct view of the display 84. It will be appreciated that the anterior-posterior length of the measurement head 18 is primarily determined by the structure used to advance the probe 12 (or, in the case of a non-contact tonometer, the structure used to generate and release the air pulses). Applicants have found that in order to provide an unobstructed direct view of the eye during measurement to an adult operator having an interpupillary distance in the range of approximately 54 mm-74 mm, the lateral width of the measurement head 18 must be limited to approximately 37 mm. Therefore, given the housing structure and other hardware required for mounting the internal measurement components in the measurement head 18, the light sources 30A, 30B must be maintained within the lateral distance LD of 25 mm to ensure direct view of the eye by the operator during measurement.

[0042] As described above, when the ophthalmic instrument 10 is positioned near the eye in preparation for measurement, the area detector 40 captures a positioning image of the eye, and the captured positioning image is converted from an analog format to a digital format by the signal processing electronics 60. The image evaluation module 82 evaluates the digital positioning image to provide information indicating the positioning state of the ophthalmic instrument 10 relative to the eye in three dimensions X, Y and Z. In order to enable image evaluation, the ophthalmic instrument 10 is calibrated using a fake "calibration eye", such as a fake eye made of glass, to capture at least one calibration image, from which positioning calibration information is determined and stored in the memory 70. The calibration eye can be, for example, a glass spherical ball with an eight millimeter radius, which is approximately the average radius of curvature of the anterior surface of the human cornea. The calibration image is captured when the ophthalmic instrument 10 is in an ideal three-dimensional position relative to the calibration eye in order to perform the measurement. For example, the ideal three-dimensional position can correspond to a situation in which the measurement axis 11 intersects the corneal vertex and is substantially perpendicular to the local corneal surface at the corneal vertex, and the tip P3 of the probe 12 is at a predetermined working distance WD from the corneal surface. In the current embodiment, the predetermined working distance WD may be six millimeters, however, the predetermined working distance WD may also be another value. In the case where the ophthalmic instrument 10 is a rebound tonometer, calibration may be performed using a calibration tool that is combined with a calibration eye and is directly installed in the ophthalmic instrument 10 along the measurement axis 11 instead of the probe 12. For example, the calibration eye may be installed at the end of a shaft similar to the probe shaft 12A, whereby the calibration tool shaft may be releasably and coaxially retained in the front coil 15 and the rear coil 16 of the ophthalmic instrument 10. The calibration tool may be configured such that when the calibration tool is installed in the ophthalmic instrument 10, the calibration eye is positioned such that, if the probe 12 is installed in the ophthalmic instrument 10 instead of the calibration tool, the vertex of the calibration eye intersects the measurement axis 11 at a Z-axis position corresponding to the predetermined working distance WD from the front tip of the probe 12. In the case where the ophthalmic instrument 10 is a non-contact tonometer, the calibration tool can have a mounting shaft sized to be slidably received within an axial channel of a fluid pulse (e.g., air puff) release tube so as to align the calibration eye on the measurement axis 11 at an ideal Z-axis working distance from the outlet end of the release tube for calibration purposes.

[0043] Fig.10An example of a calibration image 48 captured by the area detector 40 when the ophthalmic instrument 10 is in a predetermined ideal three-dimensional measurement position relative to the calibration eye is shown, and the calibration image is digitized by the signal processing electronics 60. The calibration image 48 represents a reflected light image of the facing surface area of ​​the calibration eye when illuminated by the first light source 30A and the second light source 30B. Therefore, the calibration image 48 includes a first source image 52A corresponding to the first light source 30A and a second source image 52B corresponding to the second light source 30B. The image evaluation module 82 can be programmed to evaluate the calibration image 48 to determine position coordinates XA, YA of the first source image 52A and position coordinates XB, YB of the second source image 52B, wherein the position coordinates represent the position of the corresponding source image in the two-dimensional sensing surface of the area detector 40. For example, the coordinate values ​​can be based on pixel values ​​counted relative to the origin angle of the sensing surface of the area detector 40, such as Figure 8 As shown. Evaluating calibration image 48 to determine the location of source images 52A, 52B may involve finding the group of pixels that records the highest intensity of a particular color corresponding to the color of light source 30A, 30B. For example, where area detector 40 is a red-green-blue (RGB) color sensor and light source 30A, 30B is a red LED, red, green, and blue pixel color separation may be analyzed to distinguish the red LED reflections defining source images 52A, 52B from the rest of calibration image 48. Exclusion criteria may be applied to the location, size, intensity, and / or separation of source images 52A, 52B to prevent erroneous location detection. The centroids of each of source images 52A, 52B may be calculated to determine the respective two-dimensional locations (XA, YA) and (XB, YB) of source images 52A, 52B.

[0044] The two-dimensional positions (XA, YA) and (XB, YB) of the source images 52A, 52B in the calibration image 48 may be stored directly in the memory 70 and / or used to calculate the three-dimensional calibration position coordinates (XA, YA) stored in the memory 70. CAL , Y CAL , Z CAL For example, the three-dimensional calibration position coordinates (X CAL , Y CAL , Z CAL ) can be calculated as follows. CAL , which corresponds to the ideal horizontal left-right position of the ophthalmic instrument 10 relative to the eye, can be calculated as the average X position of the two source images 52A, 52B in the calibration image 48:

[0045] X CAL =(XA+XB) / 2

[0046] Y CAL, which corresponds to the ideal vertical up-down position of the ophthalmic instrument 10 relative to the eye, can be calculated as the average Y position of the two source images 52A, 52B in the calibration image 48:

[0047] Y CAL =(YA+YB) / 2

[0048] Z CAL , which corresponds to the ideal working distance position of the ophthalmic instrument 10 along the measurement axis 11 relative to the eye, can be calculated as the horizontal spacing between the two source images 52A, 52B in the calibration image 48:

[0049] ZCAL=XB-XA

[0050] It can be appreciated that the horizontal spacing between the source images 52A, 52B is inversely proportional to the working distance. In other words, as the working distance of the ophthalmic instrument 10 from the eye decreases, the horizontal spacing between the source images 52A, 52B will increase, and as the working distance of the ophthalmic instrument 10 from the eye increases, the horizontal spacing between the source images 52A, 52B will decrease.

[0051] The two-dimensional positions (XA, YA) and (XB, YB) of the source images 52A, 52B and the three-dimensional calibration position coordinates (X CAL , Y CAL , Z CAL ) may be individually and / or collectively considered to be “positioning calibration information”. Positioning calibration information determined through calibration of the ophthalmic instrument 10 as described above may be stored in the memory 70 for later use during a normal (i.e., non-calibration) measurement process to determine when the ophthalmic instrument 10 is close enough to the ideal three-dimensional measurement position to allow measurement initiation.

[0052] Fig.11A , Fig. 11B and Fig. 11C An example of a locator image 50 captured by the area detector 40 during a normal measurement process is shown, which is displayed to the operator on the display 84 along with a superimposed locator target 90 and a locator icon 92. As with the calibration image 48, the area detector 40 generates a plurality of pixel signals that collectively represent each locator image, and the pixel signals are digitized by the signal processing electronics 60 to provide a digital locator image 50. Fig.11A , 11B 11C, the portion of the eye to be measured including the pupil of the eye is within the field of view of the area detector 40 and is visible in the positioning image 50. Similar to the calibration image 48, each positioning image 50 may include a first source image 52A corresponding to the first light source 30A and a second source image 52B corresponding to the second light source 30B.

[0053] The positioning target 90 represents the ideal three-dimensional position of the ophthalmic instrument 10 relative to the eye. The center of the positioning target 90 is set on the display 84 at the coordinates (X CAL , Y CAL , Z CAL ) CAL Value and Y CAL The size of the fitting portion 91 of the positioning icon 90 can be based on the three-dimensional calibration coordinates (X CAL , Y CAL , Z CAL ) CAL For example, the positioning target 90 may include a CAL , Y CAL , Z CAL ) A continuous or segmented ring for centering and scaling. Other shapes and forms can be used to locate the target 90, such as a cross or a square.

[0054] The positioning icon 92 represents the current three-dimensional position of the ophthalmic instrument 10 relative to the eye. The image evaluation module 82 may be configured to generate the positioning icon 92 by calculating the current three-dimensional position coordinates (X, Y, Z) based on the two-dimensional positions (XA, YA) and (XB, YB) of the source images 52A, 52B in the positioning image 50, rendering the positioning icon 92 so that the center of the positioning icon is located at an XY position on the display 84 corresponding to the X value and Y value of the current three-dimensional position coordinates (X, Y, Z), and scaling the size of the positioning icon 92 based on the Z value of the current three-dimensional position coordinates (X, Y, Z). The three-dimensional calibration position coordinates (XA, YA) may be calculated based on the calibration image 48. CAL , Y CAL , Z CAL ) In the same manner, the current three-dimensional position coordinates (X, Y, Z) are calculated based on the positioning image 50, as described above. In the illustrated embodiment, the positioning icon 92 is in the form of a ring, however, other shapes and forms, such as a cross or a square, may also be used.

[0055] The image evaluation module 82 may be configured to output the digital positioning image 50, the positioning target 90, and the positioning icon 92 to the display 84, wherein the digital positioning image 50, the positioning target 90, and the positioning icon 92 are superimposed to provide a positioning guide image displayed on the display 84 for guiding the operator to position the ophthalmic instrument 10 relative to the eye for measurement. The center of the positioning icon 92 may be located at the XY position indicated by the current three-dimensional position coordinates (X, Y, Z) in the displayed guidance image. For example, in Fig.11AIn FIG. 1 , the center of the positioning icon 92 is located above and to the right of the center of the positioning target 90, which indicates that the measurement axis 11 of the instrument 10 is below and to the left of the corneal apex and the instrument 10 must be moved upward and to the right (i.e., the operator is guided to move the instrument 10 in the direction from the positioning target 90 toward the positioning icon 92). As another example, in FIG. Fig. 11B In FIG. 1 , the center of the positioning icon 92 is located directly below and to the left of the center of the positioning target 90, which indicates that the measurement axis 11 of the instrument 10 is directly above and to the right of the corneal apex, and the instrument 10 must be moved slightly downward and to the left. Fig. 11C In the example shown, the center of the positioning icon 92 and the center of the positioning target 90 are approximately in the same position, indicating that the instrument 10 is in an ideal XY alignment position where the measurement axis 11 intersects the corneal apex.

[0056] The positioning icon 92 may be scaled based on the Z value of the current three-dimensional position coordinate (X, Y, Z) so that the size of the positioning icon is inversely proportional to the working distance of the ophthalmic instrument 10 from the eye along the measurement axis 11 (i.e., as the ophthalmic instrument 10 moves closer to the eye along the measurement axis 11, the positioning icon 92 becomes larger in the displayed positioning guide image). When the positioning icon 92 corresponds in size to the fitting portion 91 of the positioning target 90, for example, Fig. 11C As shown, the ophthalmic instrument 10 is at a predetermined desired working distance WD from the cornea for measurement. Fig.11A In the example, the instrument 10 is too far from the eye for the measurement, and in Fig. 11B In this embodiment, the instrument 10 is too close to the eye for the measurement.

[0057] As described above, the image evaluation module 82 may be configured by stored software instructions to calculate a position difference representing the current three-dimensional position of the ophthalmic instrument 10 represented by the coordinates (X, Y, Z) and the position difference represented by the calibration coordinates (X, Y, Z). CAL , Y CAL , Z CAL ) represents the difference between the ideal three-dimensional position of the ophthalmic instrument 10. For example, the position difference (ΔX, ΔY, ΔZ) can be calculated as follows:

[0058] ΔX=X-XCAL,

[0059] ΔZ=ZZ CAL ,as well as

[0060] ΔY=Y-YCAL-ΔZ.

[0061] When calculating ΔY, subtracting ΔZ compensates for changes in the camera angle as the Z distance from the eye changes (i.e., changes in the elevation angle θE of the viewing axis 42). Proper positioning of the instrument 10 relative to the eye for the purpose of measurement can be determined by whether the calculated position difference is within a predetermined positioning tolerance for the purpose of measurement. For example, in order to be within a predetermined positioning tolerance, the current X, Y pixel position of the instrument 10 must be within the pixel position X. CAL , Y CAL The absolute value of ΔZ must be less than or equal to a predetermined Z axis tolerance expressed in pixels. In spatial coordinates, it has been found that the measurement axis 11 is preferably within a radius of 1 mm from the corneal vertex in the X and Y positioning directions, and within ±1.5 mm of the ideal working distance in the Z positioning direction, although other values ​​may be used. Instead of requiring that the current X, Y pixel position of the instrument 10 is within the pixel position X, the absolute value of ΔZ must be less than or equal to a predetermined Z axis tolerance expressed in pixels. In spatial coordinates, it has been found that the measurement axis 11 is preferably within a radius of 1 mm from the corneal vertex in the X and Y positioning directions, and within ±1.5 mm of the ideal working distance in the Z positioning direction, although other values ​​may be used. CAL , Y CAL The predetermined radius can be limited to the pixel position X CAL , Y CAL A bounding box centered on , whereby each of ΔX and ΔY must be within its respective tolerance.

[0062] The appearance attribute of the positioning icon 92 may depend on whether the calculated position difference is within a predetermined positioning tolerance for measurement purposes. In this way, the positioning guidance image displayed to the operator can indicate to the operator whether an acceptable positioning has been achieved. The appearance attribute may be the color of the positioning icon 92. Thus, if the calculated position difference is not within the predetermined positioning tolerance (i.e., the instrument 10 is not correctly positioned in the three-dimensional space for measurement), the positioning icon 92 may be generated to have a predetermined first color, such as yellow. This may be considered a "NO GO" appearance of the positioning icon 92, and if the calculated position difference is within the predetermined positioning tolerance (i.e., the instrument 10 is correctly positioned in the three-dimensional space for measurement), the positioning icon 92 may be generated to have a predetermined second color different from the first color, such as green. This may be considered a "GO" appearance of the positioning icon 92. The appearance attribute may be an attribute other than color, such as an on / off blink rate applied to the positioning icon 92, and more than one appearance attribute of the positioning icon 92 may be controlled depending on whether the calculated position difference is within the predetermined positioning tolerance.

[0063] 12 and 13 are now referenced to describe the manual and automatic measurement modes, respectively, of the ophthalmic instrument 10. The menu navigation / selection buttons 86 may be used to select a selected measurement mode, either manual or automatic.

[0064] FIG. 12 illustrates the manual measurement mode of the instrument 10. In step 100, the positioning image 50 is captured by the area detector 40. In steps 102, 104, 106, and 108, the source image coordinates (XA, YA) and (XB, YB) are determined, the current positioning coordinates (X, Y, Z) and position differences (ΔX, ΔY, ΔZ) are calculated, and the size (scaling) and position of the displayed positioning icon 92 are adjusted. These steps are described in detail above. Then, a decision block 112 determines whether the calculated position difference is within the positioning tolerance predetermined for the measurement purpose. If not, the appearance attribute of the positioning icon 92 is set to or maintained as a "NO GO" appearance in step 110, but if so, the appearance attribute of the positioning icon 92 is set to a "GO" appearance in step 114. These steps are also described in more detail above. The process proceeds from step 110 or step 114 to a decision block 116. Decision block 116 awaits a signal generated in response to the operator pressing the measurement button 20, and when the button is pressed, the measurement is initiated in block 118. If the measurement button 20 is not pressed within a predetermined period of time, the flow returns to step 100. Thus, if the operator fails to quickly press the measurement button 20, the positioning must be re-evaluated to account for any intervening movement of the instrument 10 relative to the eye.

[0065] The automatic measurement mode shown in FIG. 13 is similar to the manual mode with respect to steps 100, 102, 104, 106, 108, and 112. However, if decision block 112 determines that the calculated position difference is within the predetermined positioning tolerance for the measurement purpose, the flow directly branches to step 118 and the measurement is automatically initiated (i.e., the operator does not have to press the measurement button 20 to initiate the measurement). For the automatic measurement mode, the image evaluation module 82 can be connected to the microcontroller 80 and configured to send a position confirmation signal to the microcontroller when the calculated position difference is within the predetermined positioning tolerance, and the microcontroller 80 can automatically initiate the measurement in response to the position confirmation signal. If decision block 112 determines that the calculated position difference is not within the predetermined positioning tolerance for the measurement purpose, the flow proceeds to decision block 116 to wait for the measurement button press signal, and the measurement is initiated in block 118 when the button 20 is pressed. If the measurement button 20 is not pressed within a predetermined time period, the flow returns to step 100.

[0066] The positioning system of the present disclosure provides several practical benefits for handheld ophthalmic instruments. By keeping the measuring head 18 of the instrument as narrow as possible, the amount of parallax error for an operator using the instrument in manual mode is reduced. By limiting the lateral distance occupied by the first and second light sources 30A, 30B, the size and number of pixels of the area detector 40 can be reduced, which improves the processing speed to avoid the lag between the displayed positioning guide image and reality. In addition, in the case where the cornea of ​​the eye being measured is an asymmetric cornea, if the first and second light sources 30A, 30B are too widely spaced, the effect of corneal asymmetry is amplified. This allows the instrument to obtain measurements at different areas of the cornea (such as the limbus) without affecting the positioning system error like a positioning system with a wider spaced light source. In summary, by placing the first and second light sources 30A, 30B and the area detector 40 in a smaller area, the undesirable effects of corneal curvature are reduced.

[0067] Although the disclosure describes exemplary embodiments, the detailed description is not intended to limit the scope of the appended claims to the specific embodiments set forth. The claims are intended to cover such alternatives, modifications, and equivalents of the described embodiments that may be included within the scope of the claims.

Claims

1. An ophthalmic instrument for measuring an ophthalmic parameter of an eye, the ophthalmic instrument comprising: Measuring axis; a first light source spaced from the measurement axis, the first light source directing a first illumination beam along a first illumination axis; a second light source spaced apart from the measurement axis and the first light source, the second light source directing a second illumination beam along a second illumination axis; an area detector spaced from the measurement axis and from the first light source and the second light source, the area detector having a viewing axis, wherein when the ophthalmic instrument is positioned proximate the eye in preparation for measurement, the area detector captures a positioning image of the eye, the positioning image comprising a first source image corresponding to the first light source and a second source image corresponding to the second light source, and wherein the area detector generates a plurality of pixel signals that collectively represent the positioning image; signal processing electronics connected to the area detector for receiving the plurality of pixel signals and converting the plurality of pixel signals into a digital positioning image; a memory storing positioning calibration information corresponding to an ideal three-dimensional position of the ophthalmic instrument relative to the calibration eye, wherein the positioning calibration information is based on a calibration position of the first source image and a calibration position of the second source image in a calibration image captured by the area detector when the ophthalmic instrument is in the ideal three-dimensional position relative to the calibration eye; as well as an image evaluation module configured to evaluate the digital scout image to determine current positioning information corresponding to a current three-dimensional position of the ophthalmic instrument relative to the eye, wherein the current positioning information is based on a current position of the first source image and a current position of the second source image in the digital scout image; The image evaluation module is further configured to compare the current positioning information with the positioning calibration information stored in the memory, and calculate a position difference representing the difference between the current three-dimensional position of the ophthalmic instrument relative to the eye and the ideal three-dimensional position of the ophthalmic instrument relative to the calibrated eye.

2. The ophthalmic instrument according to claim 1, wherein: The first illumination axis and the second illumination axis are coplanar with the measurement axis and form an angle bisected by the measurement axis.

3. The ophthalmic instrument according to claim 2, wherein: The first light source and the second light source are mounted within a lateral distance less than or equal to 25 mm.

4. The ophthalmic instrument according to claim 2, wherein: The observation axis is coplanar with the measurement axis.

5. The ophthalmic instrument according to claim 4, wherein: The first illumination axis and the second illumination axis are arranged in a horizontal plane containing the measuring axis, and the observation axis is arranged in a vertical plane containing the measuring axis.

6. The ophthalmic instrument according to claim 4, wherein: The first illumination axis and the second illumination axis converge at a first point along the measurement axis within the field of view of the area detector, and the observation axis intersects the measurement axis at a second point spaced from the first point along the measurement axis.

7. The ophthalmic instrument of claim 6, further comprising a working distance reference point on the measurement axis, wherein: The distance between the working distance reference point and the second point is greater than the distance between the working distance reference point and the first point.

8. The ophthalmic instrument according to claim 1, wherein: The first light source, the second light source and the area detector intersect a plane normal to the measurement axis.

9. The ophthalmic instrument of claim 1 further comprising a display connected to the image evaluation module, wherein: The image evaluation module is also configured to generate a positioning icon representing the current three-dimensional position of the ophthalmic instrument relative to the eye, and output the digital positioning image and the positioning icon to the display, wherein the digital positioning image and the positioning icon are superimposed to provide a positioning guide image displayed on the display.

10. The ophthalmic instrument of claim 9, wherein the positioning icon is scaled such that a size of the positioning icon is inversely proportional to a working distance of the ophthalmic instrument from the eye along the measurement axis.

11. The ophthalmic instrument according to claim 9, wherein: The appearance attributes of the positioning icon depend on whether the calculated position difference is within a predetermined positioning tolerance for measurement purposes.

12. The ophthalmic instrument according to claim 1, wherein: The ophthalmic instrument comprises a controller for initiating measurement, wherein the image evaluation module is connected to the controller and is further configured to send a position confirmation signal to the controller when the calculated position difference is within a predetermined positioning tolerance, and the controller automatically initiates the measurement in response to the position confirmation signal.

13. The ophthalmic instrument according to claim 1, wherein: The ophthalmic instrument is either a rebound tonometer that advances a probe along a measurement axis toward the eye or a non-contact tonometer that releases a pulse of fluid along a measurement axis toward the eye.

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