DEVICE AND METHOD FOR DETECTING TEAR FILM RUMPLETE

Abstract

A device and method for detecting tear film rupture comprising a backlit translucent plate equipped with a target (10) positioned in front of at least one eye (101) of a patient (100) and having a pattern that reflects onto the patient's eye, at least one digital photographic camera (21, 22) connected to a computing system (30) equipped with image processing and analysis means, a camera lens pointing towards the patient's eye to photograph a reflection of the pattern of the target (10) onto the patient's eye, wherein the target (10) is provided with a series of lines in the form of alternating transparent and opaque horizontal or vertical lines (12) constituting said pattern, and at least one aperture opposite the camera lens. Figure 2

Description

Title of the invention: DEVICE AND METHOD FOR DETECTING TEAR FILM RUPTURE Technical field

[0001] The invention relates to the field of detecting dry eye syndrome. Prior art

[0002] Tests for assessing dry eye syndrome include a test in which practitioners use fluorescein and directly observe the evolution of a patient's tear film. This so-called invasive test generally gives a time to the appearance of a first tear film break.

[0003] There is also a non-invasive breakup time test which assesses the quality of the tear film and which makes it possible to determine the time between a blink of the eyelid and a breakup of the tear film and which uses the reflection on the cornea of ​​a target provided with a pattern consisting of concentric circles and radial lines.

[0004] When a film break occurs, the reflected pattern exhibits distortions of the lines and / or circles or missing areas.

[0005] The images of the reflected pattern are acquired in sequence by a camera and processed by a computerized processing system which analyzes the evolution of the pattern over time to detect deformations of the pattern and deduce the time of appearance of the film rupture zones.

[0006] Currently available devices often use patterns consisting of concentric circles and radial lines. This causes problems of several kinds:

[0007] given the shape of the targets, and the coverage of the cornea by disc sectors, the spatial resolution is intrinsically less good at the edges of the field than in the center.

[0008] In the center of the field, where the radial lines converge, it is difficult to determine the deformation of a pattern.

[0009] Increasing the spatial resolution would require tightening the pattern of the target. However, circle deformation detection algorithms that require finding the most probable circles in the image, evaluating whether a point in the image belongs to a probable circle and calculating the distance of a given point to the circle to which it is supposed to belong are complex and the processing and calculation time to detect the rupture zones from the image is significant.

[0010] It is therefore clear that: on the one hand the devices presenting the classic pattern of concentric circles and radial lines suffer from a lack of homogeneity in spatial resolution, on the other hand increasing the resolution at the edge of the field is penalizing on calculation times.

[0011] Due to the low resolution of this method, the measurement may give imprecise and overestimated values ​​of the occurrence of ruptures. Technical problem

[0012] Thus there is a real uncertainty about the occurrence of the phenomenon of rupture of the ocular film and in addition, the algorithms for detecting deformations of circles which require finding the most probable circles in the image, evaluating whether a point of the image belongs to a probable circle and calculating the distance of a given point to the circle to which it is supposed to belong are complex and the processing and calculation time to detect the rupture zones from the image is significant. In addition, as seen above, the measurement precision is low and the machines using this principle are not sensitive enough to measure small ruptures, in particular because the resolution decreases when one moves away from the center of the pattern of circles and rays. Statement of the invention

[0013] The invention improves the situation and firstly proposes using a device comprising a pattern made up of light and dark lines and observing the reflection of this pattern on the cornea.

[0014] To do this, the invention proposes, on the one hand, a tear film rupture detection device comprising a backlit translucent plate provided with a target positioned in front of at least one eye of a patient and provided with a pattern reflected on the patient's eye, at least one digital photographic camera connected to a computing system internal or external to the measuring device provided with image processing and analysis means, a camera lens pointing towards the patient's eye in order to photograph a reflection of the pattern of the target on the patient's eye,for which the target is provided with a series of lines in the form of alternating transparent lines and opaque horizontal or vertical lines constituting said pattern and at least one opening facing the lens of the camera and for which the transparent lines forming on the backlit translucent plate light lines reflected on the patient's eye while the opaque lines are reflected as dark lines, the image processing and analysis means are configured to detect deformations of said light or dark lines of the pattern of the target reflected on the patient's eye and identify the tear film breaks revealed by these deformations.

[0015] The device of the present invention based on the detection of clear lines or dark in an alternation of light and dark lines avoids the problems of devices with circular pattern targets and allows fine detection of film breaks, although it appears at first glance unsuitable for an eye which has a spherical curvature.

[0016] Furthermore, because the resolution of the pattern remains homogeneous over the entire measured area, the present invention makes it possible to carry out a series of measurements tracing the evolution of the growth of the tear film breaks.

[0017] The features of the device set out in the following paragraphs may optionally be implemented. They may be implemented independently of one another or in combination with one another:

[0018] The lines of the series of lines are preferably parallel lines.

[0019] The width of the lines advantageously increases from a center line of the target towards edges of the target.

[0020] the sight is provided with a cylindrical curvature along a vertical generator.

[0021] The target is advantageously of sufficient dimensions to produce an image on a major part of the cornea of ​​the patient's eye or eyes, for example it is designed to encompass a major part of the human ocular field.

[0022] The image processing and analysis means may advantageously comprise means for converting the image into gray levels.

[0023] The image processing and analysis means may advantageously comprise anisotropic bandpass filtering means.

[0024] The image processing and analysis means may advantageously comprise means for analyzing the image according to successions of pixels perpendicular to the direction of the lines, means for searching for light or dark segments in said successions of pixels, means for quantifying the size of said light or dark segments and for eliminating segments whose size is incompatible with an image of the lines of the pattern.

[0025] The image processing and analysis means may advantageously comprise means for marking / cataloging light or dark segment objects adapted to carry out a reconstruction of first objects corresponding to branches of light or dark lines of the pattern and to carry out an elimination of second objects of shape not compatible with said light or dark lines.

[0026] The image processing and analysis means may advantageously comprise means for calculating the connection of branches of light or dark lines on the same axis, means for calculating a polynomial regression on the data of light or dark lines so as to calculate RMS curves representative of edges of said lines and means for calculating the detection of tear film breakage zones on image points of the edges of lines whose distance from said curve is beyond a given tolerance value.

[0027] According to another aspect of the present application which can be used independently of the target described above, the device can comprise means for tracking the patient's eye or eyes based on iris recognition and tracking.

[0028] These means here make it possible to recalibrate the detected tear film breaks in relation to the eye analyzed but could be used in other contexts where iris tracking is desired.

[0029] According to a particular aspect of the device of the present application, the backlit translucent plate carrying the target and the camera(s) are integrated into an ophthalmic measuring device such as an ophthalmological frame provided with a support for resting the patient's head or integrated into a helmet worn by the patient.

[0030] The present application further relates to a method for detecting tear film breaks by means of a device above which comprises an eyelid blink detection providing a time origin and at least one sequence comprising a succession of image captures and calculation of break zones from the time origin and up to a following eyelid blink.

[0031] The method features set out in the following paragraphs may optionally be implemented. They may be implemented independently of one another or in combination with one another:

[0032] The method may comprise taking an image every 0.2 to 0.5 seconds and preferably every 0.3 seconds.

[0033] The method advantageously comprises, for each image taken, a succession of processing and analysis steps comprising: - conversion of the image into grayscale; - filtering the converted image using an anisotropic bandpass filter to reduce vignetting and homogenize the brightness of the image; - a search for light or dark segments column by column in the image, a step of quantifying the size of said light or dark segments and a step of eliminating segments whose size is incompatible with a correspondence with lines of the pattern; - a step of marking / cataloging light segment objects or dark segments, of reconstructing first of said objects corresponding to branch objects of lines of the pattern and a step of eliminating second of said objects of shape not compatible with said lines of the pattern; - a step of connecting branches of lines of the same level and a step of calculating a polynomial regression on the line data in order to calculate an RMS curve of the line edges; - a calculation of tear film rupture zones by calculating the distance of the points of line edges to said curve, said break zones corresponding to the line edges whose distance from said curve is greater than a given tolerance value.

[0034] In this method, anisotropic filtering and polynomial regression are image processing means which contribute to rapid image processing and good detection of defects caused by tear film breaks.

[0035] According to one aspect of the application that can be used in another method, the method comprises steps of tracking the patient's eye or eyes using an iris tracking method. These steps here make it possible to reposition the detected tear film breakup zones relative to the analyzed eye.

[0036] The eye tracking steps may include: - a first transformation of the image by the application of an anisotropic bandpass filter applied in the direction of the width of the eye to produce pairs of rising dark to light and falling light to dark transitions along a horizontal axis of the eye; - segmentation of the image to search for pairs of rising and falling transitions which form segments which must be representative of bright areas in the image; - image filtering that eliminates light segments from the central area containing the pattern and from the upper and lower areas of the image; - taking into account the light segments, the other areas of the image no longer being considered in this analysis and a first calculation of an RMS circle of the iris circumference from the right ends of the light segments to the left of the image and the left ends of the light segments to the right of the image; - a step of deleting points too far from the RMS circle; - for the remaining points, a new RMS circle calculation step (93) to follow the contour of the iris.

[0037] The application further provides a computer program comprising instructions for implementing the break detection method and the eye tracking method when this program is executed by a processor.

[0038] This program may be stored in a non-transitory recording medium, readable by a computer, on which is recorded a program for implementing the method when this program is executed by a processor.

[0039] The application finally proposes a target for implementing the device of the invention which is produced by means of a transparent polymer film provided with opaque lines printed or screen-printed on said film and comprising at least one hole surrounded by an opaque frame in a median zone of the target, said film being shaped to be positioned on a backlit translucent plate of the device. Brief description of the drawings

[0040] Other characteristics, details and advantages of the invention will appear on reading the detailed description below, and on analyzing the appended drawings, in which:

[0041] [fig. 1] is a flat front view of a target provided with a pattern of the invention;

[0042] [fig.2] is a schematic view of a device of the present application;

[0043] [fig.3] shows a first example of a measuring support usable in the context of the present application;

[0044] [fig.4] represents an image of a patient's eye following a first stage of treatment ;

[0045] [Fig.5A], [Fig. 5B], [Fig. 5C], [Fig. 5D], [Fig. 5E] represent various stages of processing of the image of the eye of figure 4;

[0046] [Fig.6A], [Fig. 6B] represent details of Figure 5E;

[0047] [fig.7] represents an image of the eye of figure 4 after image analysis;

[0048] [fig.8] represents an image of a patient's eye looking towards a camera;

[0049] [Fig.9A], [Fig. 9B], [Fig. 9C] represent steps of determining the position of the iris of the eye of Figure 8 according to one aspect of the application;

[0050] [fig.10] represents an image of a patient's eye whose gaze is moving away from a camera;

[0051] [Fig.HA], [Fig. 11B], [Fig. 11C] show steps of determining the position of the iris of the eye of Fig. 10 according to one aspect of the application;

[0052] [fig. 12] schematizes a method for detecting areas of tear film rupture;

[0053] [fig. 13] schematizes a process for repositioning film rupture zones lacrimal in a reference linked to the eye; Description of the embodiments

[0054] The drawings and the description below describe one or more exemplary embodiments which may therefore not only serve to better understand the objects of the present application, but also contribute to its definition, where appropriate.

[0055] The method and device for detecting tear film breaks according to the present application use a target 10 shown in Figure 1 and made from a transparent polymer film comprising a pattern 11 made with alternating straight and parallel lines 12, 13. The pattern comprises opaque lines 12, for example black lines separated by transparent lines 13 allowing the light from a light source to pass through a translucent support behind the pattern to produce clear lines so that the clear lines of the pattern are reflected on the eye or eyes of a patient.

[0056] According to the example, the pattern 11 of the target 10 comprises twelve opaque lines 12 not including the upper and lower borders of the target. These opaque lines are separated by transparent lines 13 and centered around a central translucent line. The target can be mounted on a plastic frame to make it easier to handle.

[0057] By convention, a horizontal axis will be called an axis parallel to an axis passing through the patient's eyes and a vertical axis will be called the axis perpendicular to this axis and in the example illustrated, the lines of the pattern are horizontal.

[0058] As shown in Figure 2, the target 10 on its plastic support 10b is positioned on a translucent support 10a itself pierced with holes for the camera lenses to pass through and the device uses a diffuse light source 23 behind the support of the pattern to illuminate the pattern. The reflection of the pattern is observed by one or two digital cameras and, to observe the two eyes, two digital cameras 21, 22 are provided.

[0059] The diffuse light source 23 can be produced by means of an integrating box or sphere or in a manner similar to an LCD screen backlight for example.

[0060] The target is provided with two recessed areas 14 centered in opaque frames 15 on a horizontal centerline. The recessed areas are separated by a distance corresponding to an average eye distance as shown in Figure 1. Returning to Figure 2, the cameras are positioned behind the recessed areas and are in front of the eyes 101 of the patient 100. The camera lenses film or photograph the patient's eyes through the recessed areas. The recessed areas can be replaced by transparent substrate areas of the target if the optical properties of the target substrate and its level of cleanliness are compatible with image formation (transparent and non-diffusing).

[0061] The cameras are for example CMOS type cameras with 1 / 4" sensor. According to the non-limiting example shown, the transparent zones are circular holes with a diameter adapted to the camera lenses. For cameras with optics with a focal length of the order of 4 mm, holes of the order of 14 mm are made and the opaque frames are opaque squares of the order of 16 mm x 16 mm. These frames are intended to precisely terminate the lines upstream of the holes receiving the camera lenses.

[0062] In the exemplary embodiment, the camera(s) provide images with a definition of 1920x1080 which is sufficient for film break analysis without increasing the computational load of the system.

[0063] The video or camera signals are sent to a computerized processing device 30 or calculation system, internal or external to the measuring device and, to avoid duplicating this processing device, the video signals from the two cameras pass through a multiplexer, on an electronic card 24 of the device, the multiplexer making it possible to send one or other of the video channels as desired to the measuring device. treatment 30.

[0064] The cameras film or photograph the image of the pattern lines reflected in the patient's cornea. Since the cornea at first approach can be considered as a spherical diopter, it has a significant field curvature and the image has a significant distortion. In order to at least partially compensate for the distortion and to preserve on the captured images lines whose width varies little from the median axis of the pattern towards the edge of the image, the pattern of the target comprises lines with an increasing period from the central axis of the pattern towards the edges of the support parallel to the lines. For example, a central white line can have a height of approximately 2.8 mm, the adjacent black lines a height of 2.2 mm while the last white lines have a height of 3.8 mm and the black lines preceding these white lines have a height of 2.8 mm, the progression being optimized to compensate for the curvature of a standard eye.In the method described, it is the light lines that are used to search for the break areas. The number and width of the light lines may be different from the examples given but is chosen to obtain sufficient definition for significant detection of film break areas depending on the resolution of the camera(s).

[0065] In the principle of the present application, the white lines are reflected by the corneal diopter and emerge when they are backscattered in the bulbar conjunctiva of the eye and the iris where the alternation of dark lines and light lines rather creates a more or less luminous continuous background depending on the ratio between the transparent surfaces of the target and its total surface.

[0066] In Figure 2, the target seen from above is curved around a vertical axis to form a portion of a cylinder and follow the curvature of the head of the patient 100 so that the image of the target covers a large part of the cornea.

[0067] The reasons for this are: a. Optical conjugation: The camera sees the reflection of the target by the cornea considered at first glance as a spherical mirror of radius approximately 8 mm, or 4 mm focal length. Given this short focal length, the target (the object in the optical conjugation) must be large so that the size of the image by the cornea is sufficiently large, comparable in size to the external diameter of the iris. This is what determines the size of the mask. b. The photography: For the target to be visible, light rays from the outer edges of the target must enter the pupil of the lens. Since the cornea is a highly curved mirror, the light rays reaching the cornea must be grazing at the edge of the field.

[0068] This is what justifies the curvature of the sight.

[0069] According to Figure 3 the measuring device is mounted on an ophthalmological frame with chin and forehead support comprising uprights 44, a casing 43 which integrates the cameras and which receives the target 10 on a curved frontal face in front of which the patient will place himself, chin resting on a support 45. On such a frame, the patient's eyes are at a distance from the target of approximately 50 mm for a camera focal length of 4 mm. The measuring device can also be integrated into a helmet worn by the patient.

[0070] The focal length and distance are chosen to allow the entire eye to be seen, taking into account variations in the positioning of the eye in relation to the camera (interocular distance differing from one individual to another). Then a window of interest is chosen centered on the patient's pupil, by action of the operator who points the center of the pupil on the image.

[0071] So that the lines of the sight are sharp on the image, the focus is adjusted with a wheel 42.

[0072] The purpose of the measuring method of the present application is to detect and measure the growth of areas of dry eye and tear film rupture. It comprises a repetition of shots of one or both eyes of the patient at a repetition frequency of the order of 0.2 to 0.5 seconds and in practice 0.3 seconds after a blink of the eyes or the eye.

[0073] The method is described mainly in the context of a horizontal line pattern, that is to say along an axis passing through the patient's two pupils, but is adaptable in particular by means of a 90° rotation of the pixel series processing means and the anisotropic bandpass filter described below. Furthermore, the method described in the context of the detection of light lines can be applied to the detection of dark lines.

[0074] The measuring steps in the computing system 30 comprise image processing steps which, starting from a capture of the original image of the patient's eye, comprise; - a conversion of the image into grayscale according to step 205 of figure 12 and an example of the result of which is shown in figure 4 where the image 51 of the pattern on the iris 50 is distinguished with the image of the frame 52 surrounding the lens of the camera. In this image and the original color image, the shape of the reflected light lines includes local defects (in particular irregular line edges which already reveal deformations of the tear film); - A second step 210 of figure 12 comprises an application of an anisotropic bandpass filter applied in a direction perpendicular to the direction of the reflected lines, i.e. a vertical direction and therefore on the columns of pixels of the image in the case of a test pattern with horizontal lines or a test pattern with vertical lines, the image being in this case rotated 90° to obtain clear lines oriented in a horizontal direction, and configured to keep the transitions between the gray levels clear and to suppress or attenuate the modulations of low spatial frequency and higher spatial frequency in the perpendicular direction. The image at the filter output is shown in Figure 5A. This filter has the particular utility of overcoming vignetting phenomena and defects in the homogeneity of the lighting. This transformation accentuates the lines of the eyelid 53, the clear lines 54 of the pattern of the test chart and preserves the image of the frame 55.

[0075] Then, still in the case of light lines oriented in a horizontal direction, the method comprises an analysis of the image 220 by columns of pixels according to FIG. 12 which will search for vertical light segments. The resulting image then comprises lines 56, 57, 58, 59 as shown in FIG. 5B. Once this analysis has been done, the light segments are qualified by their size, steps 230, 235. This makes it possible to eliminate segments that are too large or too short and that clearly do not correspond to line segments of the pattern, for example the segments forming part of the outline of the eyelids. At the end of this step, FIG. 5C represents the image where the column segments constituting the isolated line 61, the lines of the image of the pattern 62, the background 64 and the frame 63 remain. It should be noted that the eyelashes cause significant fragmentation of the lines 65 at the top of the image.In the case of a vertical line test pattern, the analysis and qualification of the segments is done by lines of pixels.

[0076] When the segmentation is finished, the processing method comprises a marking / cataloging algorithm 240, 250, 260 of the light segments to obtain the objects representative of light branches of lines of the pattern and to reject the light objects not having the desired shape which are then considered as artifacts. This algorithm firstly comprises a connection of the contiguous column segments to reconstitute horizontal branches. The result of this marking / cataloging is represented in FIG. 5D for which each line found is assigned a color here represented in gray levels. This cataloging makes it possible to create complete lines 70 or isolated branches 71, 72.

[0077] A next step is a connection 280 of the branches of light lines of the same level (for example of similar width and altitude) in the image then a polynomial regression 285 using a polynomial of order higher than two in order to calculate an RMS curve of the shape of the edges of the lines. This step is represented in figure 5E. In this figure we note in particular connections by the lower 74 and upper 74' RMS curves of the branches 73a, 73b of the lines broken up at the level of the image of the frame surrounding the lens of the camera and of the branches 73c, 73d of the lower line. The enlargement of figure 6A makes it possible to better distinguish the RMS curves 74, 74' between the branches 73c, 73c at the bottom of the image. Then a detection of the sites or zones of rupture of the film 290 is carried out at the places where the edges of the lines have measurement points which deviate from the shape given by the polynomial, with two criteria: - the deviation from the polynomial is greater than a threshold, - this threshold exceedance exists on several contiguous columns.

[0078] This is for example represented in figure 6B in the zone 76 where the line edge 77b of the line 77a does not reach the curve 74'.

[0079] As seen above, the method can be based on a treatment of dark lines. Grouping the transition pairs (rising and falling in the case of light lines) allows a consistency check to be made on the width of the segment obtained and to reject segments that are too wide or too narrow to be part of the image of the target. Once the branches have been determined, the polynomial regression is carried out on each side of the branch: a polynomial for the rising transitions, a polynomial for the falling transitions. The method of the invention therefore makes it possible to search for dark segments and dark lines and arrive at the same polynomial regressions and the same final result.

[0080] The result of the measurements is a map of the tear film break sites shown in Figure 7 for which the map of the break points 78 is positioned on the initial color image of the eye shown here in gray levels.

[0081] As seen above, images are captured approximately every 0.3 seconds. A time origin is defined as an eyelid blink and repeating the measurement for each image over a period of time allows the construction of a map of breaks as a function of time.

[0082] One issue to consider is that the patient's gaze may change direction during the image acquisition period.

[0083] As the camera observes the reflections of the pattern on the cornea which behaves in first approximation like a spherical diopter, the position of the image of the pattern remains almost invariant in the image delivered by the camera whereas the position of the iris changes if the patient turns his eyes. Therefore a given point of the image of the target is not linked to a fixed point of the cornea, but on the contrary to a point dependent on the direction of gaze. This implies that the measurement must be referenced in relation to the position of the observed eye and not in relation to the image of the pattern.

[0084] To do this, it is necessary to follow the position of the eye in each image. It was preferred to follow the outer contour of the iris of the eye because there is a significant contrast with the bulbar conjunctiva, which is light in color and on which there is no reflection of the target, while the pupil is more difficult to follow because of the reflection of the target, which complicates the analysis of the image.

[0085] The following method can be implemented within the scope of the present application or independently for other measurements on the eyes. This method is also independent of the orientation of the lines of the sight.

[0086] Figures 8, 9A, 9B and 9C correspond to the image processing on an eye of a patient looking at the camera and Figures 10, 11A, HBetllC correspond to the image processing on an eye of a patient whose gaze moves away from the camera.

[0087] According to figure 8, the eye 80 looks straight ahead, the image of the pattern 83 is centered relative to the iris 82 itself centered relative to the eyelid 81.

[0088] The image processing method for finding the position of the iris is shown diagrammatically in Figure 13. It comprises a first transformation of the image by applying an anisotropic bandpass filter 400 applied horizontally to detect the light transitions along a horizontal axis. In this operation, we seek to distinguish the descending transitions (light to dark) and the ascending transitions (dark to light) and for understanding, the light to dark transitions (descending transition) are translated by the dark crescent 84 of the grayscale representation of Figure 9A and the dark to light transitions (ascending transition) are translated by the light crescent 85 of Figure 9A.Parts of the image without significant transitions become medium gray, such as the crescent 86 for example, and the outline of the iris is materialized by a portion of a ring 87 which is found on the left side next to a light to dark transition and on the other side of the eye next to a dark to light transition.

[0089] Returning to Figure 13, a second operation consists of a segmentation of the image 410 to search for the pairs of rising and falling transitions, 84, 85 in Figure 9A for example, which form boundaries of the bright areas in the image, in particular around the bulbar conjunctiva. These pairs of transitions materialized by the limits 88, 89 and 90, 91 in Figure 9B frame areas 92 potentially defining the bulbar conjunctiva.

[0090] From this transformation, the method comprises, according to Figure 13, a filtering of the image 420 which removes the central zone comprising the pattern and the upper and lower zones of the image. On the remaining parts, a calculation of an RMS circle of the circumference of the iris is carried out from the right ends of the segments to the left of the image and from the left ends of the segments to the right of the image 430. For this calculation, the points too far from the RMS circle which correspond to imperfections notably caused by the eyelashes or the eyelid are rejected at step 440 and, for the remaining points, a new RMS circle is calculated to follow the contour of the iris, this circle 93 is represented in Figure 9C on the original image of the eye.

[0091] Figure 10 shows an eye 80' looking sideways and whose iris 82' is offset relative to the pattern 83'. For this position of the eye, the transitions 84', 85' around dark areas 86', 87' corresponding to homogeneous colors are shifted laterally in Figure 11A while in Figure 11B it can be seen that the arcs of circles 89' and 90' corresponding to the edge of the iris remain detectable. The application of the tracking method also leads to recreating the RMS circle 93' which will be repositioned on the original image as shown in Figure 11C. The detected tear film breaks are then relocated according to step 450 according to the position of the circle defining the outline of the iris. This makes it possible to anchor the tear film breaks to the outline of the eye rather than to the image.

[0092] This sequence is carried out for each image preferably after the analysis of the line pattern described above.

[0093] As stated above, this method is applied here to the repositioning of the rupture zones but it can also be used for other types of detection and methods using tracking of the position of an eye.

[0094] According to one aspect of the application, the device may comprise a manual trigger which arms the device, the triggering of the sequence of images then being carried out on the occurrence of an event such as a series of two blinks of the patient's eyelids. To do this, the system comprises a method for recognizing eyelid blinks which makes it possible to start the measurement sequence automatically. Similarly, the system may stop the measurement sequence automatically upon detection of a subsequent blink of the eyelids or stop the sequence automatically after a time delay, for example 15 seconds.

[0095] The shooting sequence can comprise 30 to 50 images for example and in the case of a 15 second shooting sequence with shots taken every 0.3 seconds the sequence comprises 45 images. The analysis of the images can be done after the shooting sequence and due to the chosen solution of working on a pattern made of lines, the processing time remains reduced, for example 15 seconds with a standard computer.

[0096] When the measurement is completed, the practitioner has at his disposal, on the one hand, a spatial and temporal mapping of the tear film ruptures within the corneal surface and, on the other hand, a temporal curve tracing the appearance of the tear film ruptures as a function of time. This temporal curve, and in particular its slope, will reveal the kinetics of the appearance of the tear film ruptures. This makes it possible to refine the interpretation of the examination carried out.

[0097] The invention is not limited to the examples described above, only by way of example, but it encompasses all the variants such as a distribution or a progression of the height of the different lines that may be envisaged by those skilled in the art within the framework of the protection sought. In particular, as stated above, the lines of the pattern which are horizontal parallel lines according to the example shown can be replaced by vertical lines, a rotation of the image allowing for example to apply the image processing means of detecting the deformations of the lines to this configuration without changing the direction.

Claims

Claims

1. A tear film rupture detection device comprising a backlit translucent plate provided with a target (10) positioned in front of at least one eye (101) of a patient (100) and provided with a pattern (11) reflected on the patient's eye, at least one digital photographic camera (21, 22) connected to a computing system (30) provided with image processing and analysis means, a lens of the camera pointing towards the patient's eye in order to photograph a reflection of the pattern (11) of the target (10) on the patient's eye, characterized in that the target (10) is provided with a series of lines in the form of alternating transparent lines (13) and opaque lines (12) horizontal or vertical constituting said pattern (11) and at least one opening facing the lens of the camera and characterized in that,the transparent lines forming on the backlit translucent plate light lines reflected on the patient's eye while the opaque lines are reflected as dark lines, the image processing and analysis means are configured to detect deformations of said light or dark lines of the pattern of the target reflected on the patient's eye and identify the tear film breaks revealed by these deformations.,

2. A device according to claim 1, wherein the lines of the series of lines are parallel lines.

3. Device according to claim 1 or 2, for which the width of the lines increases from a center line of the target towards edges of the target.

4. Device according to any one of the preceding claims, for which the sight (10a) is provided with a cylindrical curvature along a vertical generatrix to form a portion of cylinder and follow the curvature of the patient's head (100).

5. Device according to any one of the preceding claims, for which the image processing and analysis means comprise means for converting the image into gray levels.

6. Device according to any one of the preceding claims, for which the image processing and analysis means comprise anisotropic bandpass filtering means.

7. Device according to any one of the preceding claims, for which the image processing and analysis means comprise means for analyzing the image according to successions of pixels perpendicular to the direction of the lines, means for searching for light or dark segments in said successions of pixels, means for quantifying the size of said light or dark segments and for eliminating segments whose size is incompatible with an image of the lines of the pattern.

8. Device according to claim 7, for which the image processing and analysis means comprise means for marking / cataloging light or dark segment objects adapted to carry out a reconstruction of first objects corresponding to branches of light or dark lines of the pattern and to carry out an elimination of second objects of shape not compatible with said light or dark lines.

9. Device according to claim 8, for which the image processing and analysis means comprise means for calculating the connection of branches of light or dark lines on the same axis, means for calculating a polynomial regression on the data of light or dark lines so as to calculate RMS curves representative of edges of said lines and means for calculating the detection of tear film rupture zones on image points of the edges of lines whose distance from said curve is beyond a given tolerance value.

10. Device according to any one of the preceding claims, comprising means for tracking the patient's eye or eyes based on iris recognition and tracking so as to re-align the detected tear film breaks with respect to the eye analyzed.

11. Device according to any one of the preceding claims, for which the backlit translucent plate (10a) carrying the target (10) and the camera(s) (21, 22) are integrated into an ophthalmic measuring device (43, 44).

12. Method for detecting tear film breaks by means of a device according to any one of the preceding claims, characterized in that it comprises an eyelid blink detection providing a time origin and at least one sequence comprising a succession of image captures and calculation of break zones from the time origin and up to a following eyelid blink.

13. A method for detecting tear film breaks according to claim 13, comprising taking an image (200) every 0.2 to 0.5 seconds and preferably every 0.3 seconds.

14. Method for detecting tear film breaks according to claim 12 or 13, comprising for each image taken, a succession of processing and analysis steps comprising - a conversion of the image into grayscale (205); - a filtering (210) of the converted image by means of an anisotropic bandpass filter in order to reduce vignetting and homogenize the brightness of the image; - a search for bright or dark segments column by column (220) in the image, a step of quantifying (230) the size of said bright or dark segments and a step of eliminating (235) the segments whose size is incompatible with a correspondence with lines of the pattern;- a step of marking / cataloging (240) light segment objects or dark segments, of reconstructing (270) first of said objects corresponding to branch objects of lines of the pattern and a step of eliminating (260) second of said objects of shape not compatible with said lines of the pattern; - a step of connecting branches of lines of the same level (280) and a step of calculating a polynomial regression (285) on the line data so as to calculate an RMS curve of the line edges; - a calculation of tear film break zones (290) by calculating the distance of the line edge points to said curve, said break zones corresponding to the line edges whose distance to said curve is greater than a given tolerance value.;

15. A method of detecting tear film breaks according to any one of claims 12 to 14 comprising steps of tracking the patient's eye or eyes (400, 410, 420, 430, 440, 450) by means of an iris tracking method so as to reposition the detected tear film break areas relative to the analyzed eye.

16. The method of claim 15 wherein the eye tracking steps comprise: - a first step of transforming the image by applying an anisotropic bandpass filter (400) applied in the direction of the width of the eye to produce pairs of rising dark to light and falling light to dark transitions along a horizontal axis of the eye; - an image segmentation step (410) to search for pairs of rising and falling transitions (88, 89, 90, 91) which form segments to be representative of bright areas in the image; - an image filtering step (420) which eliminates the light segments from the central area comprising the pattern and from the upper and lower areas of the image; - a step of taking into account the light segments, the other areas of the image no longer being considered in this analysis, and a first calculation of an RMS circle of the circumference of the iris (430) from the right ends of the light segments to the left of the image and from the left ends of the light segments to the right of the image; - a step (440) of deleting points too far from the RMS circle; - for the remaining points, a new RMS circle calculation step (93) to follow the contour of the iris.

17. Computer program comprising instructions for implementing the method according to one of claims 12 to 16 when this program is executed by a processor.

18. Non-transitory recording medium readable by a computer on which is recorded a program for implementing the method according to one of claims 12 to 16 when this program is executed by a processor.

19. Target (10) for implementing the device according to any one of claims 1 to 11, characterized in that it is produced by means of a transparent polymer film provided with opaque lines (12) printed or screen-printed on said film and separated by transparent lines (13), comprising at least one hole (14) surrounded by an opaque frame (15) in a median zone of the target, said film being shaped to be positioned on a backlit translucent plate (10a, 23) of the device.

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