WO2011091804A1

WO2011091804A1 - An apparatus for quantitative cataract diagnostics

Info

Publication number: WO2011091804A1
Application number: PCT/EE2010/000003
Authority: WO
Inventors: Jaak Kikas; Agu Anijalg; Koit Mauring
Original assignee: Tartu Ülikool (University Of Tartu)
Priority date: 2010-01-29
Filing date: 2010-01-29
Publication date: 2011-08-04

Abstract

A portative apparatus for quantitative cataract diagnostics has been disclosed. That apparatus comprises a modulated light source, a photodetector, an illumination optics, means for lock-in detection of the electrical current from the photodetector and a distance meter. The photodetector may be with or without a central hole; it can be designed from a bundle of optical fibres. The photodetector having a central hole is arranged so that the patient's eye lens is illuminated with the light beam through the hole of the photodetector and the back- scattered light is measured by the photodetector. If the photodetector has no hole, then the light beam is directed to the lens by a central mirror situated in front of the photodetector. The photodetector has area extending in all directions from the optical axis of the eye, resulting in high sensitivity and uniform (in all azimuthal directions) detection of back-scattered light.

Description

AN APPARATUS FOR QUANTITATIVE CATARACT DIAGNOSTICS FIELD OF THE INVENTION

The invention refers to ophthalmology (ophthalmological diagnostic apparatus) and can be used for objective measurement of the change in the optical properties of the eye lens and also for diagnosing the extent of lenticular opacity associated with cataract development. DESCRIPTION OF THE PRIOR ART

The cataractous eye lens scatters light entering into the eye from pupil and diminishes the contrast as well as the sharpness of the image on the retina. The more developed the cataract has become, the more intensive the scattering of light is. According to this the stage of cataract can be quantitatively precisely evaluated by measuring the scattered light intensity. The opaque eye lens scatters light inside the eye, but a certain amount of the scattered light is transmitted through the pupil back outside from the eye.

The knowledge of the cataract stage is important for scheduling the operation for replacing the cataractous lens with an artificial one (IOL - Intraocular Lens) .

The method and the apparatus of detection of the back- scattered light for evaluation of the extent of clouding of the lens has been disclosed in the patent application EP 0231769 (Interzeag AG, 1987) . In the described apparatus the direction of the incident light on the lens and the direction of the scattered light from the lens to the photodetector form a big angle and part of the scattered light is masked by the iris. This is the reason why the result of the measurement with the lens opacity meter, manufactured by Interzeag, is incorrect in the case when the patient's pupil diameter is less than 4 mm (M.P. Clark, J.C. Pearson, J.C.Matthews, Influence of pupil size on measurements made with the lens opacity meter 701, British Journal of Ophthalmology 1990, 74, 526-527) . Because of the fact that detection of the scattered light takes place in one direction only, the area of the photodetector is small,. resulting in low sensitivity of the instrument.

For evaluation of a cataractous lens optical properties, a stray light meter C-Quant (Cataract Quantifier, respective patent application O2005/023103 Al) is produced by Oculus Optikgerate. The psychophysical method, used to measure the intraocular stray light, presupposes the evaluation by the patient of her/his subjective perceptions during the diagnostics. Therefore the apparatus can not be used for noncooperative patients. Also, the results obtained by the C-Quant have a subjective component, which diminishes their value.

Presently, the basic method for cataract diagnostics is examination with a slit lamp. The method is subjective and rather time consuming and needs an eye specialist.

All the instruments mentioned are stationary (not portative) , rather expensive equipment which are not suitable for cataract screening.

The prior art fails to present means for quantative objective measurement of the development of cataract with sufficient reproducibility and robustness, for reliability and consistency between different patients and the same patients in the progression of time. There is a need for a portable apparatus that provides objective, precise and quantitative measurement of the cataract stages across patients and over time.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an apparatus for quantitative cataract diagnostics. The apparatus for quantitative cataract diagnostics disclosed herein comprises a modulated light source, photodetector, illumination optics, means for lock-in detection of the electrical current from the photodetector and a distance meter. Said distance meter (which could be ultrasonic or optical) enables automatic or manual start of measurement at a fixed distance from the eye lens. Ultrasonic distance meter could be equipped with means for converging the ultrasonic beam.

In the preferred embodiment of the invention discoled herein the named photodetector has a central hole, which is arranged so that the lens is illuminated with the light beam through the central hole of the said photodetector and the light, which is back-scattered from the lens, is measured by the named photodetector. The shape of said photodetector shall be a ring or other design. The preferred embodiment of the present invention includes the ring shaped photodetector. The photodetector with a central hole can be also designed from a bundle of optical fibres, whereas the bundle terminal which collects the scattered light is having a central hole and the other terminal of the bundle of optical fibres directs the back-scattered light onto a photodetector.

Another object of the current invention is the apparatus whereas said photodetector has no hole and the eye lens is illuminated with the light beam, which is directed to the eye lens by the additional mirror, located in front of the photodetector. The shape of said mirror shall be a ring or other design. The preferred embodiment of the present invention includes the ellips-shaped mirror.

The apparatus can comprise optical means for visual inspection of the patient's eye during cataract quantitative diagnostics. The apparatus can also comprise a position sensitive photodetector for exact positioning of the apparatus in respect of the optical axis of the eye. Said position sensitive photodetector may be a quadrant photodetector. In accordance with the present invention the modulated or pulsed light is directed through the opening (hole) in the photodetector or after reflection by additional mirror onto an eye lens. The backscattered from the lens light is detected by the photodetector and the photoelectrical signal is amplified by the lock-in amplifier which eliminates the influence of any background light. The resultant voltage is converted into a digital form by the microcontroller or an analog-digital converter ADC. To ensure reproducibility of the measurements, the measurements are automatically started by the microcontroller or by an operator according to the signal from the distance meter at a specific (constant) distance from the eye. Several readings are taken and the microcontroller calculates the average which quantitatively characterises the cataract and which is indicated on the display. The results can be stored in the microcontroller's memory and/or can be sent to a computer connected to the apparatus by cable or over a wireless link. The apparatus may comprise optical means for visual inspection of the patient's eye during diagnostics, an additional light source and a beam splitter for fixing the patient's gaze to stabilize the eye position.

As disclosed herein, this backscattered light is used for determination of the cataract stage. The used photodetector has area extending in all directions from the optical axis of the eye, resulting in high sensitivity and uniform (in all azimuthal directions) detection of back-scattered light . This way the quantitative, numerically characterized cataract diagnostics is achieved by a portative apparatus disclosed herein.

Embodiments of the present invention provide an advantage over the prior art by providing an objective, quantative measurement replacement to the prevailing subjective evaluation of cataract today.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows the basic components of the apparatus for quantitative cataract diagnostics, comprising photodetector with a hole

1 - light source

2- illumination optics

3- photodetector

4 - means for lock-in detection of the optical current of the photodetector

5- distance meter

6- microcontroller

7- display

8- eye lens

9 - central hole

10 - light beam

11-light, which is back-scattered from the eye lens

12- additional light source

13- beam splitter

Fig. 2 shows the basic components of the apparatus for quantitative cataract diagnostics, comprising photodetector without a hole

1 - light source

2- illumination optics

3- photodetector 4 - means for lock-in detection of the optical current of the photodetector

5- distance meter

6- microcontroller

7- display

8- eye lens

10 - light beam

11-light, which is back-scattered from the eye lens

14-mirror

Fig. 3 depicts graphically the results of testing of the linearity of the photodetector of the current invention in comparison with the lock-in amplifier SR850 (Stanford Research Systems) .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In preferred embodiment of this invention, Fig. 1, the light beam 10 of the light source 1 is directed through the central hole 9 of the photodetector 3 into the eye lens 8. The back-scattered light 11 from the eye lens 8 is measured by the photodetector 3. In order to get good repeatability and high accuracy of the measurements, the photodetector 3 must be located at a fixed distance from the eye lens 8, which is measured by distance meter 5. The microcontroller 6 detects the output signal of the distance meter 5 and when the predetermined distance is achieved, the measurement of the photodetector signal is automatically or manually (operator-controlled) started. For fixing the gaze of ,the patient the device is equipped with the additional light source 12, which directs light onto a beam splitter 13 and further into the patient's eye.

The electrical current from the photodiode 3 is amplified by the lock in amplifier 4 and digitized by an ADC or the microcontroller 6 and the quantified result is displayed on a LCD-module 7.

According to the above the following cataract diagnostics apparatus was designed. The light emitting diode Hamamatsu L7868 served as the light source 1, the illuminaton optics 2 for collimating the light comprised a three-lens collimator GS8019 and a pinhole. The photodetector was a punched photodiode VTS2080H from PerkinElmer. The means for lock-in detection 4 of the photocurrent consisted of photocurrent preamplifier AD820 AC-coupled to instrumental amplifier INA118 followed by the low noise analog multiplier AD835 which functioned as a lock-in amplifier. The clock generator consisted of the timer circuit NE555 followed by divider by 2 (implemented by D-trigger) which ensured the square wave duty factor of 0.5 at high precision. This was vital for perfect operation of the said lock-in amplifier, implemented on the basis of the analog multiplier. The named square wave was also used for controlling the power supply of the LED. The distance meter 5 was ultrasonic UNDK10U6914 from Bauraer, which ensured a distance measuring accuracy of 0.3 mm. The microprocessor PIC18F4550 was used for digitalization of the analog output of the distance meter and for the automatic start of the scattered light measurement at a fixed distance from the lens. The microprocessor was also responsible for displaying the results on the LCD-module (EADIPS082 from Electronic Assembly) and for controlling the charging of the lithium-ion batteries.

Fig. 2 shows the apparatus where the modulated light emitted from the light source 1 is directed through the illumination optics 2 to a mirror 14, located in front of the photodetector 3. The shape of said mirror shall be a ring or other design. The preferred embodiment of the present invention includes the ellips-shaped mirror 14. The scattered from the patient's eye lens 8 light is detected by this photodetector 3. The shape of said photodetector shall be a ring or other design. The preferred embodiment of the present invention includes the ring shaped photodetector, which in combination with the ellips-shaped mirror (which has a ring-shaped shadow on the photodetector 3) form an ring-shaped active area. This ensures uniform detection of the scattered light 11 in all directions from the eye axis. The current from the photodiode 3 is amplified by the lock-in amplifier 4 and digitized by an ADC or the microcontroller 6 and the quantified result is ^■displayed on a LCD-module 7.

The accuracy of the back-scattered light detection was tested and the results are depicted on the graph of Fig. 3. The measurement results obtained by the apparatus of current invention (photodetector and the lock-in amplifier) are highly correlated with the results of the lock-in amplifier SR850 (Stanford Research Systems) . The linearity is excellent: the coefficient of correlation is 0,99998 and the offset value is almost zero.

It shows that quantitative data for cataract disgnostics measured with the portative apparatus of the current invention are as accurate as obtained by high-quality stationary device.

The embodiments described herein illustrate the principles of the invention and are not intended to be exhaustive or to limit the invention to the form disclosed; it is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

The diagnostics of the cataract is performed as follows. The operator directs the light beam of the apparatus into the centre of the patient's eye pupil and after moving the apparatus in the direction to the eye, at a fixed distance from the eye, the measurement of the backscattered light is performed. The result is displayed and stored in the memory of the apparatus. The diagnostics is very sensitive, which allows to use very comfortable for the patient low intensity light (~10 μW) . The measurements on the eye model showed, that the numerical results are precisely linearly dependent on the opacity and agree very well with the measurements performed with the commercial lock in amplifier. The immunity of the measurements ^' in respect of ambient light was tested and found that apparatus can work normally under conditions of normal lighting in the office.

Claims

1, An apparatus for quantitative cataract diagnostics comprising a modulated light source 1, illumination optics

2, photodetector 3, means 4 for lock-in detection of the optical current of the photodetector 3, distance meter 5, microcontroller 6 and display 7,

c h a r a c t e r i z e d in that said distance meter 5 enables automatic or operator-controlled start of measurement at a fixed distance from the eye lens 8 and said photodetector 3 has a central hole 9, which is arranged so that the eye lens 8 is illuminated with the light beam 10 through the hole 9 of the said photodetector

3, and the light which is back-scattered from the eye lens 8 is measured by the named photodetector 3.

2. The apparatus according to Claim 1, whereas said photodetector 3 has no hole and the eye lens 8 is illuminated with the light beam 10, which is directed to the eye lens by the additional mirror 14, located in front of the photodetector 3.

3. The apparatus according to Claims 1-2, which further comprises an additional light source 12 and a beam splitter 13 for fixing of patient's gaze to stabilize the eye position.

4. The apparatus according to Claims 1-3, whereas the photodetector 3 is ring shaped.

5. The apparatus according to Claim 1, whereas the distance meter 5 is ultrasonic or optical.

6. The apparatus according to Claim 5, whereas the said ultrasonic distance meter 5 is equipped with means for converging the ultrasonic beam.

7. The apparatus according to Claims 1-2, whereas the photodetector 3 is designed from a bundle of optical fibres, whereas the bundle may have or not have a central hole and the termini of optical fibres direct the back- scattered light onto the photodetector 3.

8. The apparatus according to Claim 1, which further comprises a position sensitive photodetector for exact positioning of the apparatus in respect of the optical axis of the eye.

9. The apparatus according to Claim 8, whereas said position sensitive photodetector is a quadrant photodetector .

10. The apparatus according to Claim 1-2, which further comprises the optical means for visual inspection of the patient's eye during diagnostics.