WO2017149181A1 - Instrument for obtaining images of the eye and associated method - Google Patents

Abstract

The invention relates to an instrument for obtaining images of the eye, comprising a light source S, the intensity of which is controlled by a neutral density filter F1, and for which the colour/wavelength is achieved using a bandpass filter F2, and also comprising: an electronic modulation device for the light emitted by the light source S, which generates structured illumination patterns; a mirror M1 that directs the light coming from the light source S towards the electronic light modulation system; at least three lenses L1, L2, L3 located between the electronic light modulation system and the eye to be studied; a diaphragm D1 connected in the plane of the pupil of the eye to be studied in order to allow control of the position at which the light enters the eye; a photodetector that measures and registers the intensity of the reflected light; a mirror M2 that directs the light leaving the eye towards the photodetector; a diaphragm D2 connected in the plane of the pupil of the eye, which determines the exit path of the light; at least one lens L4 between the diaphragm D2 and the photodetector, such that the diaphragms D1 and D2 are connected with the same plane, but are relatively displaced, in such a way that different parts of the pupil of the eye are used to project the illumination patterns in the entry beam and to collect their reflective intensity in the exit beam, and such that the electronic light modulation device and the photodetector are connected to a computer having image-processing software.

Description

 Instrument to obtain images of the eye and associated method.

Field of the Invention

The present invention relates to an instrument and a method for obtaining images of the eye, and is framed within the field of ophthalmic systems and ophthalmology.

It is of special application to obtain images of the retina of a human eye in vivo, although it also allows to obtain images of other areas of the eye, for example, to detect possible damages.

Background of the invention In the technical field of the invention it is crucial to examine the health and conditions of the retina for the early detection of unwanted alterations. This may include the monitoring of very common retinal pathologies, such as retinopathies of various kinds.

Elderly patients are the most affected by retinal pathologies and, therefore, those who most require adequate control of the retina. It is very important to diagnose and control the status of many eye diseases even in the case that patients have opacifications in the ocular media, which is very common in elderly patients.

The registration of images of the human retina is a common process that is performed in ophthalmological practice. This helps to control the patient's eye and health conditions by detecting diseases such as glaucoma, macular degeneration, diabetes and others. Early detection of a possible alteration of retinal conditions is important for potential treatment in order to prevent blindness or disease progression. Most of the cameras for observation of the fundus and ophthalmoscopes currently used incorporate conventional video cameras (based on CCD or CMOS sensors) to record images of the retina (see, for example, Moore, RD, & Hopkins , GW (1992), "CCD camera and method for fundus imaging '). The retina is illuminated and the image obtained through the entire optic of the eye is formed on the camera. In these cases the defects in the optics and opacifications of the eye will affect the images of the retina. Other ophthalmoscopes are based on the scanning of a beam that is projected onto the retina (see, for example, Webb, RH, & Hughes, GW (1981), "Laser Scanning Ophthalmoscope ", IEEE Transactions on Bio-Medical Engineering, 28 (7), 488-92), and reconstruct an image of the retina. Both procedures are rapid and non-invasive, and therefore have a common and widespread practice. In addition, there are portable ophthalmoscopes that are used and contain various lenses to give the examiner direct vision inside the patient's eye based on the Helmholtz instrument (Helmholtz, H. (1851), "Beschreibung eines Augen-Spiegels zur Untersuchung der Netzhaut im lebenden Auge ').

However, there are eye conditions that degrade the quality of the images that can be obtained from the fundus, such as the opacity of the lenses, cataracts and refractive errors in the optics of the eye (blur, astigmatism and aberrations). If these conditions are very marked, a satisfactory image of the retina cannot be obtained while using existing conventional devices. The images obtained from the background are blurred and in this way the details or areas of interest that are partially or totally hidden cannot be distinguished, making a reliable examination of the state of the retina practically impossible. The double-pass system (Santamaría, J., Artal, P., & Bescós, J. (1987), "Determination of the point-spread function of human eyes using a hybrid optical-digital method", Journal of the Optical Society of America A, Optics and Image Science, 4 (6), 1 109-1 1 14) bypass this problem using only a fraction of the eye's optics (sub-openings), to guide spatially encoded light on the retina. In addition, and given the nature of the procedure, the sensitivity and robustness of the method is greatly increased. Therefore, the optical system avoids most of the optics in which the quality of the beams would be compromised and thus the impact of aberrations is reduced (see Artal, P., Pujol, J., Oscar, S. , Benito, A., & Pérez, G. (2010), "System and method for measuring light scattering in the eyeball or eye region by recording and processing retina! Images'), and the projections of the patterns are minimally interfered with by any type of opacity found in the cornea and lens of the eye These opacities can be cataracts, corneal infections, corneal dystrophies, corneal lesions and opacity of the posterior capsule.

No prior art optical instrument is capable of obtaining images through the opaque optics of the eye without any loss of image quality, thus allowing the retina to be examined even if direct vision is blocked by a scattered and diffused medium.

An instrument is therefore necessary to obtain images of the eye that avoids the limitations of a conventional camera ophthalmoscope, allowing the possibility of obtaining clear images through the opacities in the eye. Summary of the invention

Thus, the object of the present invention is to provide an instrument for obtaining images of the eye that resolves the aforementioned drawbacks.

The present invention relates to an instrument for obtaining images of the eye, which comprises a light source S whose intensity is controlled by a neutral density F1 filter, and for which the color / wavelength is achieved using a step F2 filter. of band, and that additionally includes:

- an electronic light modulation device illuminated by the light source S, which generates structured lighting patterns, - a mirror M1 that directs the light coming from the light source S towards the electronic light modulation system,

- at least three lenses L1, L2, L3 located between the electronic light modulation system and the eye to be studied,

- a conjugated diaphragm D1 in the plane of the pupil of the eye to be studied to allow control of the position of light entry into the eye,

- a photodetector that measures and records the intensity of the reflected light,

- an M2 mirror that directs the exit light of the eye towards the photodetector,

- a conjugated diaphragm D2 in the plane of the pupil of the eye, which determines the path of exit of the light, - at least one lens L4 between diaphragm D2 and the photodetector, so that diaphragms D1 and D2 are conjugated with the same plane but are relatively displaced, so that different parts of the pupil of the eye are used to project the illumination patterns in the input beam and to collect their intensity of reflection in the output beam, and such that the device Electronic light modulation and photodetector are connected to a computer with image processing software.

The invention also provides a method of obtaining images of the eye using an instrument of the invention, and comprising the following steps:

Project a large number of structured lighting patterns on the retina sequentially and at high speed Measurement and recording of the intensity reflected in the photodetector for each pattern of light projected on the retina

Computer reconstruction of the image of the retina using image processing software from the intensities obtained and their respective lighting patterns.

This method allows to obtain images of the retina for different areas of the visual field and with the advantage over other ophthalmoscope alternatives of the prior art to obtain good quality images, even in cases where the eye has significant opacities in the ocular media , including cases of patients with cataracts or corneal opacities.

Also, the method of the invention does not require conventional image recording cameras.

Brief description of the drawings

The object of the present invention will be illustrated in a non-limiting manner, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic of the optical system with the instrument to obtain images of the eye of the invention.

Figure 2 shows a close-up image of the eye with the input light beam and the output light beam. Figure 3 shows a front view of the eye with the input light beam and the output light beam.

Figure 4 shows a simulation of a comparison between a conventional ophthalmoscope and an ophthalmoscope of the invention.

DETAILED DESCRIPTION OF THE INVENTION The instrument of the invention uses a double-pass configuration to obtain images with structured illumination on the retina. The term double step refers to the fact that the resulting intensity of the scalar product of the retina image is measured through the same optics that are used to make the image of the lighting pattern. The difference in the present invention compared to the above instruments is based on the fact that 1) the retina is illuminated with a set of spatially known lighting patterns encoded at a high repetition rate and 2) the use of a photo- detector to record the intensity of the reflected light that contains information of the internal products instead of a camera to form the image of the retina.

Therefore, to obtain an image of the retina, the image needs to be computed computationally from the intensities obtained and its respective lighting pattern, which is generated in a specifically developed image processing software interface. It is possible to do it at high speed enough to record the images of the retina at real-time video speed.

Figure 1 shows a possible version of the proposed double-pass ophthalmoscopic system. Structured (or spatially encoded) illumination is generated by a Digital Micro-Mirror Device (DMD) (or other possible form of electronic light modulation) and the image is formed on the retina. The DMD is illuminated by a light source S, coherent or incoherent. The intensity of the source is controlled by a neutral density filter F1 and the color / wavelength of the light used can be achieved using a bandpass filter F2. The light coming from the source is directed through the mirror M1 towards the DMD. Pattern images are formed in the retina through lenses L1, L2 and L3.

Diaphragm D1 is conjugated in the plane of the pupil of the eye that allows the control of the position of entry of the lights in the eye. The reflected intensity is collected by the detector through the L3, L2 and L4 lenses. Diaphragm D2 is conjugated in the plane of the pupil and therefore determines the path of exit of the light. Diaphragms D1 and D2 are conjugated simultaneously on the plane of the pupil but on different transverse positions so that different parts of it are used to project the patterns on the retina and collect the reflected intensity. Therefore, overlapping and interaction between both light paths is avoided.

Figure 2 shows a close-up image of how the input beam and the output beam are using different parts of the eye's optics and therefore do not overlap each other.

Figure 3 shows the front view of one eye. The figure describes a possibility of how light enters and leaves the eye through the pupil. The white squares are the images of the conjugated diaphragms D1 and D2 that indicated the input position of the projected light and the output position of the reflected intensity.

Figure 4 shows a simulation of the images obtained by a conventional ophthalmoscope using a camera (type CCD or CMOS) in which an increase in opacity in the optics of the eye blurs the image and the fine details are not recognizable. In In comparison, a simulation of images received through the proposed single-pixel camera ophthalmoscope proposed here (lower images) where the increase in opacity and light diffusion affects the quality of the images much less, the details of which are The most recognizable retina. Main provisions of the invention

The system has a double-pass configuration where a structured light pattern is projected onto the retina and its corresponding reflected intensity is measured. As can be seen in Figure 1, structured lighting is created in the Digital Micro-Mirror Device (DMD). The DMD consists of multiple mirrors of micrometric dimensions that allow modulating the light beam in two different states with high spatial resolution. Therefore, a set of lighting patterns (binary) are generated with the DMD that are generated in advance using a computer.

The patterns can have a size of up to N x N pixels only limited by the size of the DMD. The DMD is illuminated with a broadband light source S, its intensity can be controlled with a neutral density filter F1. In addition, the wavelength of light can be selected by using an F2 filter. Behind the filters is a mirror that directs the light towards the DMD. The images of the patterns are formed in the retina of the eye through the lenses L1, L2 and L3. Diaphragm D1 is conjugated in the plane of the pupil of the eye (telescope through L2 and L3). Therefore, it allows control of the part of the pupil that is used to project the patterns. The intensity is measured with a detector through the lenses L3, L2 and L4 such that the diaphragm D2 is conjugated with the plane of the pupil of the eye and therefore controlling the part of the pupil that is used. Diaphragms D1 and D2 are relatively displaced so that different parts of the pupil are used for projection and measurement as can be seen in Figure 3. For each projected pattern the corresponding inner product (intensity) is measured. After a finite number of projected patterns and recorded intensities, the image of the retina is calculated by means of:

(Equation 1)

Image = ^ Intensity> i Pattern., where Pattern _xy (x _and y are pixel values in an N x N matrix) is denoted as Pattern. Each intensity measured is multiplied with each element of its corresponding standard matrix resulting in a sub-image. The sum of all sub-images appears in the final image. To achieve an image with a size N x N, it is necessary to project N ² patterns chosen from an orthonormal base of the vector space of matrices of dimension NxN.

In this way the number of patterns grows quadratically with the size of the image, which translates into an increase in the time required for its measurement; Note that the projection device needs a finite time to encode a lighting pattern.

Since the time required is crucial for retinal imaging that may be in motion, there are two different techniques that can be applied to reduce the imaging time:

1) Image compression / detection method: a limited set of n patterns (“N ² ) is projected onto the retina and its corresponding reflected intensity is measured using the photodetector. After visualizing the finite number of n patterns that is significantly less than N ² (up to 90% lower), a mathematical statistical method / algorithm is used to reconstruct the image of the retina from the limited set of available data. Depending on the desired resolution, the calculation time may be longer than the initial reduction time, showing fewer patterns.

2) Adaptive imaging / detection method: This method avoids patterns of long display times and high image reconstruction times. First, a complete set of N ² patterns needs to be visualized. Then, the measured intensities by pattern are sorted according to the highest intensity responses. Then, only a limited amount of high responsiveness patterns

(up to 90% lower) is displayed and its corresponding intensity is measured. From there, the image of the retina can be reconstructed using equation 1. These reconstructed images closely resemble the reconstructed original images with the total number of patterns. In another arrangement, the system has a double-pass configuration, as described above, where spatially encoded patterns are projected onto the retina and their corresponding reflection intensity is measured while using the same optical device. For each projected pattern the corresponding intensity in the inner product (intensity). After a finite number of projected patterns and recorded intensities, an image of the retina can be calculated by means of:

where Patron _xy (x _and y are the pixel values in a matrix of pattern N x N) is reformed to Patron. Each intensity measured is multiplied with each corresponding element matrix pattern that results in a sub-image. The sum of all sub-images gives rise to the final image. For the full spatial resolution of N x N, N ² patterns have to be projected. To subsequently decrease the signal-to-noise ratio of each pattern shown, it is followed consecutively by its inverse pattern and therefore the number of projected patterns for 2 x N ² that introduces less noise into the reconstructed image of the retina is doubled.

In addition, if we are able to locate points of interest with less diffusion in the pupil / cornea, we could use that area as an entry point and direct the light there, again to decrease beam distortions. Another advantage is the use of temporary multiplexed lighting and its consecutive measurement of the reflected intensity. In a finite time we project thousands of patterns, which vary from low to high spatial frequency, on the retina. For each projected pattern, we measure the reflected intensity that comes from the retina and subsequently an image of the retina is computed computationally based on the principle of the single pixel camera (Miao, X., & Amirparviz, B. (2015), " Single Pixel Camera ").

The proposed proposal is therefore, very significantly different from the current common ophthalmoscopes where a single flash is performed to obtain a complete image of the retina. Our method offers images with an improved signal-to-noise (SNR) when compared to traditional imaging due to the amount of measurements that are taken and all light from the retina is collected. This can also lead to a reduction in the power of the light with which we illuminate the eye, which improves patient comfort. The light that is reflected in the retina, also passing through the optic of the opaque and diffuse eye, does not modify the quality of the final image since no camera is used as occurs in obtaining images with the traditional approach. The proposed system measures the reflected background intensity of the retina for a given structured lighting pattern, thus, the possible deteriorated optics of the eye (by the reasons mentioned above) acts to reduce the magnitude of the intensity of the reflected light but does not affect the quality of the reconstructed final image.

Therefore, we are able to reconstruct an image with reasonably good quality without the loss of vital details, as schematically depicted in Figure 4. This represents a clear advantage over the conventional ophthalmoscope where opacities in the eye's optics make blurred the image and deteriorate the crucial details. To date, there is no optical instrument capable of obtaining images through the opaque optics of the eye without loss of image quality, allowing the retina to be examined even if direct vision is blocked by a diffused and diffused medium. This device gives the opportunity to detect possible damage to the retina before any type of eye surgery. In this way, you can help support the examiner to improve your prediction of the results of, for example, cataract surgery if you would like to know the condition of the retina before treatment.

According to an embodiment of the invention, the wavelength range of the illumination can be adjusted from 400 nm to 1000 nm.

According to an embodiment of the invention, the light source S may be coherent or incoherent.

According to an embodiment of the invention, sub-apertures of different sizes are used for measurements of illumination and reflected intensity.

According to another embodiment of the invention, the instrument additionally comprises means for alignment with the eye to be studied.

Although embodiments of the invention have been described and represented, it is evident that modifications within its scope can be introduced therein, which should not be considered limited to said embodiments, but only to the content of the following claims.

Claims

1 .- Instrument for obtaining images of the eye, comprising a light source S whose intensity is controlled by a neutral density F1 filter, and for which the color / wavelength is achieved using a bandpass F2 filter, characterized because it additionally includes: - an electronic light modulation device illuminated by the light source S, which generates structured lighting patterns, - a mirror M1 that directs the light coming from the light source S towards the electronic light modulation system, - at least three lenses L1, L2, L3 located between the electronic light modulation system and the eye to be studied , - a conjugated diaphragm D1 in the plane of the pupil of the eye to be studied to allow control of the position of light entry into the eye, - a photodetector that measures and records the intensity of the reflected light, - an M2 mirror that directs the eye's exit light towards the photodetector, - a conjugated diaphragm D2 in the plane of the pupil of the eye, which determines the path of exit of the light, - at least one lens L4 between the diaphragm D2 and the photodetector, so that the diaphragms D1 and D2 are conjugated with the same plane but are relatively displaced, such that different parts of the pupil of the eye are used to project the patterns of illumination in the input beam and to collect its intensity of reflection in the output beam, and such that the electronic light modulation device and the photodetector are connected to a computer with image processing software. 2. An instrument for obtaining images of the eye, according to claim 1, wherein the electronic light modulation device is a DMD Digital Micro Mirror Device. 3. An instrument for obtaining images of the eye according to any of the preceding claims, wherein the illumination wavelength range can be adjusted from 400 nm to 1000 nm. 4. - An instrument for obtaining images of the eye, according to any of the preceding claims, wherein the light source S can be coherent or incoherent. 5. - An instrument for obtaining images of the eye, according to any of the preceding claims, in which sub-apertures of different sizes are used for measurements of illumination and reflected intensity. 6. - An instrument for obtaining images of the eye, according to any of the preceding claims, which additionally comprises means for alignment with the eye to be studied. 7. - Method for obtaining images of the eye, which employs an instrument of claims 1 -10, characterized in that it comprises the following steps: - Projected sequentially and at high speed a large number of structured lighting patterns on the retina Measurement and recording of the intensity reflected in the photodetector for each pattern of light projected on the retina Computer reconstruction of the image of the retina using image processing software from the intensities obtained and their respective lighting patterns. 8. - Method for obtaining images of the eye, according to claim 7, wherein the images are generated at real-time video speed, real-time videos being produced by continuously repeating the process of projecting structured patterns and reconstructing the Illuminated object after measurement of reflected intensity.