WO2016189243A1

WO2016189243A1 - Device for detecting a state of the cornea of the eye and associated method

Info

Publication number: WO2016189243A1
Application number: PCT/FR2016/051220
Authority: WO
Inventors: Myriam ZERRAD; Gabriel SORIANO; Claude Amra
Original assignee: Centre National De La Recherche Scientifique; Université D'aix-Marseille
Priority date: 2015-05-26
Filing date: 2016-05-24
Publication date: 2016-12-01
Also published as: FR3036607A1

Abstract

The invention relates to a device (1) for detecting a state of the cornea (3) of the eye (5) comprising a contrast imaging unit (11) with laser granularity, having: a source (13) of coherent electromagnetic radiation intended for lighting up the cornea (3) of the eye (5); a detector (15) of at least one speckle image diffused by the cornea (3) of the eye (5); a unit (17) for processing the speckle image configured to establish a normalised histogram of the speckle image, and to determine the order of the gamma distribution which makes it possible to extrapolate the normalised histogram, the state of the cornea being associated with a first state corresponding to a surface diffusion coming from the surface state of the cornea (3) if the extrapolated gamma distribution is of the order N=1, and the state of the cornea being associated with a second state corresponding to a diffusion coming from the volume of the cornea (3) if the extrapolated gamma distribution is of order N>1.

Description

Device for detecting a state of the cornea of the eye and associated method

The present invention relates to a device for detecting a state of the cornea of the eye and an associated method.

When examining the eye of an ophthalmologist, the eye usually examines the cornea through the slit lamp's biomicroscopy, to see if it is damaged or not. This technique requires little training, but it does not allow an accurate analysis of the cornea.

In particular, this visual examination does not detect weak alterations not visible to the naked eye by the ophthalmologist, which are for example premises of a potentially more serious complication.

There are other more sophisticated and comprehensive analytical techniques such as specular non-contact microscopy.

However, this technique is complex, expensive and time consuming. Admittedly, specular microscopy makes it possible to collect qualitative information (cell morphology) and quantitative information (cell density) from the endothelial image, but it only allows a small surface area of about 1 mm ^{2 to} be examined and can be summarized most often counting corneal cells per unit area.

The present invention aims to provide a device for reliably detecting alteration of the cornea at an early stage.

For this purpose, the present invention provides a device for detecting a state of the cornea of the eye comprising a contrast unit with laser granularity ("speckle imaging unit" in English), presenting

• a source of coherent electromagnetic radiation intended to illuminate the cornea of the eye, A detector of at least one speckle image diffused by the cornea of the eye,

A speckle image processing unit ("speckle image") configured to establish a standardized histogram of the speckle image ("speckle image" in English), and to determine the order of the Gamma law for extrapolating the normalized histogram, the state of the cornea being associated with a first state corresponding to a surface diffusion from the surface state of the cornea (3) if the extrapolated Gamma law is of order N = 1, and the state of the cornea being associated with a second state corresponding to a diffusion from the volume of the cornea (3) if the extrapolated Gamma law is of order N> 1.

Thus, the device for detecting a state of the cornea of the eye according to the invention makes it possible to quickly and efficiently distinguish whether a cornea is healthy or whether a cornea has an impaired state.

Indeed, the inventors have found that for a healthy cornea, the light scattered by the cornea comes essentially from the surface of the cornea. In this case, the order of the Gamma law extrapolating the normalized histogram is N = 1.

While for a cornea for example poorly hydrated or sick, the cornea reveals a more heterogeneous structure and it is a volume diffusion. In this case, the order of the Gamma law extrapolating the normalized histogram is N> 1, typically N = 2 or N = 4.

The device according to the invention may furthermore have one or more of the following characteristics taken alone or in combination:

The coherent radiation source comprises for example a laser.

In one aspect, the radiation source is almost monochromatic. In another aspect, the coherent radiation source is monochromatic, especially in the ultraviolet, the visible or the infrared.

The device may further include an optical fiber for delivering radiation from the radiation source to the cornea.

Said detector of at least one speckle image ("speckle image" in English) comprises for example a CCD camera.

According to yet another aspect, the device comprises a measurement head integrating said detector of at least one speckle image and at least a part of the optical fiber, the output of the optical fiber and said detector being held in a measurement position relative to each other.

The invention also relates to a method for detecting a state of the cornea of the eye using a laser granularity contrast imaging unit ("speckle imaging unit" in English), in which

The cornea of the eye is subjected to observation with coherent electromagnetic radiation,

At least one speckle image is detected, diffused by the cornea of the eye,

• the speckle image is exploited by establishing a standardized histogram,

The histogram is extrapolated by a Gamma law, the state of the cornea being associated with a first state if the extrapolated Gamma law is of order N = 1 and the state of the cornea being associated with a second state if the extrapolated Gamma law is of order N> 1.

The coherent electromagnetic radiation comes in particular from a laser. The shimmer image can be taken by a camera with a CCD sensor.

Other advantages and characteristics will appear on reading the description of the invention, as well as the following figures in which:

FIG. 1 shows a diagram of a device for detecting a state of the cornea of the eye according to one embodiment of the invention,

FIG. 2 shows an example of a measured speckle image,

FIG. 3 shows an example of normalized and extrapolated histogram, and

FIG. 4 shows a flowchart of the various steps of the method according to the invention.

In the figures, the identical elements are identified by the same references.

The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments may also be combined to provide other embodiments.

In the description, it is possible to index certain elements or parameters, such as for example first element or second element as well as first parameter and second parameter, or first criterion and second criterion, and so on. In this case, it is a simple indexing to differentiate and name elements or parameters or criteria close but not identical. This indexing does not imply a priority of one element, parameter or criterion with respect to another, and it is easy to interchange such denominations without departing from the scope of the present description. FIG. 1 shows an example of a device 1 for detecting a state of the cornea 3 of the eye 5. In this diagram, the eye 5 is partially and schematically represented with, in addition, the iris 7 and the lens 9.

This device comprises a laser granularity contrast imaging unit 11 (also called "speckle imaging unit" or "speckle imaging unit").

This laser granularity contrast imaging unit 11 comprises a source 13 of coherent electromagnetic radiation intended to illuminate the cornea 3 of the eye 5. This source 13 of coherent radiation may be a laser, or even any other source of purity. spectral image giving rise to the presence of speckle images (also called "speckle images" or "speckle images"). In a conventional manner, the source is continuous, but it can also be pulsed provided that the duration of the pulsation does not significantly alter the spectral purity, in accordance with the time-frequency relationship. Note that for a standard HeNe laser, the linewidth of the radiation source 13 is of the order of the picometer. Finally, the emission wavelength will generally be between the ultraviolet and infra-red, and we can use an emission around low-cost sources (He-Ne, diodes ...).

Indeed, it is important that the power of the incident radiation is not too great not to cause damage to the eye during the measurement. For that we will be able to be based on the standards in force in the field of the optical protection of the eye. It should be noted that the incident power can be considerably reduced, since the integration time of the CCD matrix can be increased in parallel.

As can be seen in FIG. 1, the coherent electromagnetic radiation source 13 is not placed directly in front of the eye 5 for the measurement, but an optical fiber 14 is interposed between the coherent radiation source 13 and the eye 5. to guide and route the light emitted by the source 13 to the eye 5. However, alternatively the lighting can also take place directly, without fiber.

The laser granularity contrast imaging unit 11 further comprises a detector 15 of at least one speckle image scattered by the cornea of the eye. The detector 15 is for example a camera equipped with a CCD sensor (for "Charge coupled device" in English), as a CCD camera. If necessary, this matrix detector can be linear (recording by rows of pixels), or replaced by any matrix or linear detection system.

The imaging unit 11 further comprises a unit 17 for processing the speckle image connected to the detector 15 which transmits the image taken as data. This processing unit 17 is configured to establish a normalized histogram of the speckle image, and to determine the order of the Gamma law, also called Gamma distribution in the theory of probabilities, for extrapolating the normalized histogram.

According to the embodiment of FIG. 1, the device 1 comprises a measurement head 19 integrating said detector 15 with at least one speckle image and at least a part of the optical fiber 14. The output of the optical fiber 14 and said detector 15 are held in a measuring position with respect to each other. The value of the detection angle can be chosen almost arbitrarily in the angular range, as well as the illumination angle. In general, for practical reasons, the illumination may be almost normal incidence, and the detection will be in a direction taken between 15 ^° and 45 ^°

Note that in the case of a radiation source 13 having a greater linewidth, a narrow-band interference filter may be placed at the output of the radiation source 13 or in front of the detector 15. Figure 2 shows an example of a recorded shimmer image approximately 13mm x 13mm in size by a CCD camera. There is a clear distinction between the "granular" character of the image, which is a characteristic of the shimmer image. We can thus take into account a large part of the cornea 3, see the entire surface of the cornea 3.

From such a shimmer image, a histogram is established, that is to say, for each level of intensity measured I, the number of points N (I) for which this level is obtained and normalizing, the histogram can be transformed into a probability density law (pdf - "propability density function"), which is shown in FIG.

The measurements can then be extrapolated by a Gamma law

where N is the order of the Gamma law. By extrapolating the measurement points of the normalized histogram, we can therefore determine the order of the Gamma law.

In FIG. 3, a first standardized histogram of measurements 50 has been plotted which can be extrapolated by a Gamma law of order N = 1 and a second measurement histogram 52 which can be extrapolated by a Gamma law of order N = 2. .

Of course, when the measurements are taken, only one measurement histogram is detected. In addition, the steps of processing the speckle image, in particular to establish the normalized histogram and to extrapolate the normalized histogram, are carried out by the processing unit 17 which comprises for this purpose calculation and processing means, in particular a microprocessor and memories loaded with software for this purpose.

The inventors have found that when the order of the Gamma law is N = 1 (curve 50), the detected diffusion is a surface diffusion coming from the surface of the cornea 3. In this case, it is a healthy cornea and well hydrated. When the order of the Gamma law is N> 1, for example N = 2, 4, the detected diffusion is a diffusion from the volume of the cornea 3 and more particularly of its heterogeneities.

In other words, the Gamma law provides information on the origin of the scattered light, while quantifying the level of heterogeneity, which is characteristic of the microstructure of the cornea 3.

Thus, by subjecting the cornea 3 of the eye 5 to a device 1 according to the invention, it is quite easy to determine any alteration of said cornea 3, even before the known examinations allow to see already larger corneal damage. . This allows a doctor to prescribe preventive treatments to stabilize or improve the state of the cornea 3. It may therefore be reduced by early detection and appropriate treatment the need to resort to heavier interventions for example of the surgical type.

An examination with the device 1 according to the invention would also detect the effect of a corrective lens of view on the eye. Indeed, we can quickly detect if the corrective lens does not allow sufficient hydration of the cornea 3, which will allow the ophthalmologist to choose a Lens model more suited to the patient's eye, before irreversible damage is produced.

The invention also relates to a method for detecting a state of the cornea of the eye using a laser granularity contrast imaging unit whose steps are illustrated in FIG. 4.

In a first step 100, the cornea 3 of the eye 5 is subjected to coherent radiation.

Then according to a step 102, at least one speckle image scattered by the cornea 3 of the eye 5 is detected.

In a step 104, the speckle image is exploited by establishing a standardized histogram.

Finally, in a step 106, the normalized histogram is extrapolated by a Gamma law to determine the order of the Gamma law.

We associate the state of the cornea with a first state if the extrapolated Gamma law is of order N = 1 and we associate the state of the cornea with a second state if the extrapolated Gamma law is of order N> 1.

It is thus clear that the device according to the invention gives a doctor a valuable preventive detection tool making it possible to easily detect an alteration, even a small one, of the cornea 3.

In addition, the detection can be performed non-intrusively and quickly directly on a patient without it being hindered.

Finally, the application of the detection device and the method associated with biological tissues other than the cornea, such as for example animal or plant tissue, can be extended.

Thus, the device or the method can be applied to analyze plant material (leaves, plants, roots, stems, etc.) on samples taken or in real time (in fields / crops). The Gamma law governing the shimmer image histogram will be driven by the structure of this biological tissue, a structure that depends on its nature, its state of stress, its environment, and the level of maturation.

Claims

1. A device (1) for detecting a state of the cornea (3) of the eye (5) comprising a laser granularity contrast imaging unit (11) having

A source (13) of coherent electromagnetic radiation for illuminating the cornea (3) of the eye (5),

A detector (15) of at least one speckle image scattered by the cornea (3) of the eye (5),

A speckle image processing unit (17) configured to establish a normalized histogram of the speckle image, and to determine the order of the Gamma law for extrapolating the normalized histogram, the state of the cornea being associated with a first state corresponding to a surface diffusion from the surface state of the cornea (3) if the extrapolated Gamma law is of order N = 1, and the state of the cornea being associated with a second state corresponding to a diffusion from the volume of the cornea (3) if the extrapolated Gamma law is of order N> 1.

2. Device according to claim 1, characterized in that the source (13) of coherent electromagnetic radiation comprises a laser.

3. Device according to claim 1 or 2, characterized in that the source (13) of radiation is almost monochromatic.

4. Device according to any one of claims 1 to 3, characterized in that the source (13) of coherent radiation is monochromatic, especially in the ultraviolet, the visible or in the infrared.

5. Device according to any one of claims 1 to 4, characterized in that it further comprises an optical fiber (14) for conveying radiation from the source (13) of radiation to the cornea (3).

6. Device according to any one of claims 1 to 5, characterized in that said detector (15) of at least one speckle image comprises a CCD camera.

7. Device according to claim 5 taken together with any one of claims 1 to 4, or 6, characterized in that it comprises a measuring head (19) incorporating said detector (15) of at least one image of shimmering and at least a portion of the optical fiber (14), the output of the optical fiber (14) and said detector (15) being held in a measuring position with respect to each other.

8. A method of detecting a state of the cornea of the eye using a laser granularity contrast imaging unit, wherein the cornea of the eye is subjected to electromagnetic radiation consistent (100),

At least one speckle image scattered by the cornea of the eye (102) is detected,

• the speckle image is exploited by establishing a standardized histogram (104),

The histogram is extrapolated by a Gamma law (106), the state of the cornea being associated with a first state if the extrapolated Gamma law is of order N = 1 and the state of the cornea being associated with a second one. state if the extrapolated Gamma law is of order N> 1.

9. The method of claim 8, characterized in that the coherent electromagnetic radiation is from a laser.

10. The method of claim 8 or 9, characterized in that the speckle image is taken by a camera (15) having a CCD sensor.