WO2002032309A1

WO2002032309A1 - Apparatus for detecting a retinal or optical nerve disorder

Info

Publication number: WO2002032309A1
Application number: PCT/CH2001/000616
Authority: WO
Inventors: Christof W. Burckhardt
Original assignee: Burckhardt Christof W
Priority date: 2000-10-16
Filing date: 2001-10-15
Publication date: 2002-04-25
Also published as: EP1370177A1; FR2815240B1; FR2815240A1

Abstract

The invention concerns an apparatus for automatically detecting the initial stage of a retinal or optical nerve disorder in a person's eye, in particular glaucoma, wherein eye flickering is measured at different frequencies of a modulated light source, by determining a deLange curve relative to that eye for said frequencies. The measuring apparatus (10) comprises a housing (11), provided with a triggering button (12) and a pushbutton (13) enabling the person whose eye is being examined to indicate when a white light source (22) has stopped blinking. Said source, automatically frequency- and modulation-controlled by a microprocessor, is housed in an eye cup (16) connected to the apparatus (10) by a connection (17). Light-emitting diodes (14) emitting different colours, indicate the result of the examination provided by a computing unit incorporated in the microprocessor. A communication port (15) enables the apparatus to be connected to peripheral units.

Description

APPARATUS FOR DETECTING A RETEN IENNE DISEASE OR OPTICAL NERVE

TECHNICAL FIELD The present invention relates to an apparatus for detecting a retinal affection or the optic nerve of a person's eye, in particular glaucoma, comprising a modulated light source for measuring the perception threshold of flickering of the eye. eye at different predetermined frequencies of said light source, by determining a deLange curve relating to this eye for these frequencies, a strategic unit of measurement associated with means for generating and varying the frequency and modulation of the light emitted, means to transmit this modulated light to the eye of the person to be examined, means for analyzing the signals emitted by the eye as a function of the light signal received and for transforming them into a final value defining the degree of progress of the affection and can be displayed, and means for displaying this final value.

PRIOR ART For many years, the eye has been the subject of numerous researches in spite of which many phenomena remain unexplained to date. In particular, with regard to the detection of affections which affect the retina and the optic nerve and which can lead to blindness and in particular glaucoma, it is very difficult to be able to diagnose this disease very early in order to be able to treat it. as quickly as possible. Currently, among the many psychophysical detection methods used, only the method based on the measurement of the threshold of perception of the flicker of the eye and the determination of the deLange curve seems to give promising results, the other known methods not making it possible to detect illness only when the damage it has already caused is significant. In particular, in the case of the detection of glaucoma, which is a condition which causes degeneration of the nerve optics by destroying nerve cells, the most frequently used techniques are conventional computerized perimetry, commonly performed with a device called “Octopus” and observation of the fundus of the eye. However, these measurements only allow visual field defects to be detected when approximately 30 to 40% of the cells are affected, which does not correspond to the initial stage of the disease.

We know from international publication WO 91/14399 a papillometer whose semi-automated operation is based on this method and which was developed with the aim of being used as an instrument for early diagnosis. However, this device did not give conclusive results because the information extraction from the deLange curve did not work in an objective and reliable way.

Other devices have also been developed to allow this early diagnosis.

The detection device described in publication WO / 29627 is based on the observation of a specific target allowing the control of different areas of the visual field of a subject by measuring the limit contrast at which the subject still discerns this target.

Furthermore, the European publication EP 0 962 188 relates to an apparatus which is also based on the measurement of the flicker of the eye by varying the luminance of a target on a screen.

Currently, none of these devices can achieve the desired goal reliably.

Statement of the invention

Other studies leading to the subject of the invention have allowed another approach to the problem by considering the effect produced by glaucoma on the deLange curve and basing the modeling of this curve on the theory of filters. In this approach, we admit that the flicker limit curve results from the interaction of three types of filters, namely:

- receptors in the retina, - the optic nerve for transmission,

- the brain for reception.

On this basis, we consider that the optic nerve has the characteristic of a low-pass filter associated with a cut-off frequency fi and that the signal from the brain has the characteristic of a low-pass filter associated with a cut-off frequency. f ₂ . In the case of a normal eye, fi is substantially close to f _{2 |} which translates a correspondence between the optic nerve and the brain, therefore a correct transmission of visual information to the brain. On the other hand, in the event of an abnormality of the eye due to a deterioration of the transmission element, that is to say the optic nerve, the cut-off frequency f _{1 (} which is associated with it, becomes lower than the frequency f _2. Consequently, we can deduce that a ratio f ₂ / fi greater than 1 indicates an anomaly of the optic nerve. The various measurements carried out make it possible to highlight the variation in slope at the level of the deLange curve the medium frequency part associated with the optic nerve and the high frequency part associated with the brain.

The present invention therefore proposes to overcome the drawbacks of the prior art by providing an apparatus which makes it possible to make reliable measurements of the flicker threshold of the eye by determining the deLange curve, which is precise, which operates automatically. , without operator, and which makes it possible to obtain a rapid measurement making it possible to identify any affection at its initial stage.

To this end, the device as defined in the preamble, is characterized in that the strategic measurement unit is arranged to obtain said curve automatically, in that the device comprises means arranged to compare the curve obtained and a reference curve and determine, for each frequency, the ratio l <existing between the frequency f ₂ , corresponding to the cutoff frequency of the signal coming from the brain of the person in response to the perception of the end of the flashing of the light signal emitted, and the frequency f _{1 (} corresponding to the cutoff frequency of the signal coming from the optic nerve of this person in response to the perception of the end of the flashing of this same light signal emitted, and in that the means for analyzing the signals transmitted comprises a calculation unit arranged to sum the values of k obtained for all the frequencies and to obtain, automatically, said final value of k.

Advantageously, the apparatus comprises means arranged so that, at each frequency, the modulation of light decreases linearly, on a logarithmic scale, from 100% to 0.2% with a linearity factor equal to 0, 8.

In the preferred embodiment, the means for generating and varying the frequency are arranged to generate a linear series of frequencies, on a logarithmic scale, located between 7 Hz and 50 Hz with a linearity factor equal to 1.25.

In the preferred embodiment of the invention, the apparatus comprises an analog sinusoidal signal generator and the means for varying the modulation of the light emitted comprise a modulator arranged to transform these analog sinusoidal signals into digital sinusoidal signals in sigma modulation -delta.

Preferably, the strategic measurement unit comprises a memory arranged to store, during the measurement process, the different values of the limit modulation of the light signal emitted. In order to transform the information collected by the strategic unit into values that can be displayed, the calculation unit includes means for calculating a non-linear regression.

Preferably, the strategic measurement unit associated with the generator, the modulator and the memory, as well as the calculation unit are produced in the form of a single microprocessor. They can however be produced in the form of separate microprocessors.

In all embodiments of the apparatus, the light source is at least one light emitting diode, emitting white light, associated with a current amplifier.

Preferably, the means for displaying the final values of k are constituted by at least two light-emitting diodes whose emission color is linked to the value of the calculated ratio k.

The apparatus according to the invention advantageously comprises means arranged so that, at each frequency, the person communicates to the strategic measurement unit the end of the perception of the flashing of the light signal emitted.

Brief description of the drawings

The invention will be better understood with reference to the description of an embodiment given by way of nonlimiting example and to the accompanying drawings, in which:

FIG. 1 is a perspective view of the measuring device according to the invention,

FIG. 2 is a diagrammatic representation of the components of the apparatus illustrated in FIG. 1, and Figures 3A and 3B are schematic views, respectively side and in section along line II of Figure 3A, of another embodiment of the light source fitted to the measuring device according to the invention.

Best way to realize the invention

With reference to FIG. 1, the measuring device 10 according to the invention comprises a housing 11, intended to house the various components which will be described below with reference to FIG. 2. This housing is provided on one of its faces lateral of an engagement button 12 and on its front face means allowing the person to communicate information to the device. In the illustrated embodiment, these means are in the form of a pusher 13. The housing 11 is also provided with means for displaying the values obtained, in the form of at least two light-emitting diodes 14 whose color of emission and the number can vary according to the nature and the precision of the information which one wants to give. It is also equipped with a housing and a socket (not shown) respectively arranged to receive supply means which can be a set of stick batteries or a block external to the device, the latter being supplied at low voltage, that is to say a voltage less than or equal to 12 volts. A communication port 15 of the RS 232 type allows its connection to peripheral units such as a computer or a printer.

An eye 16, intended to be placed in front of the eye to be checked and which will be described in more detail below, is connected to the housing 11, in a manner known per se, by flexible means 17 partially shown.

Figure 2 illustrates in the form of a block diagram the main components of the measuring device 10 and the connection of these components with the different parts forming this device. A strategic measurement unit 20, linked to the engagement button 12, is intended to control, by means of a signal generator 21, the variations in frequency and modulation of a light source 22 which, in this apparatus , is a diode light emitting white light, disposed in the eyepiece 16. This diode 22 is controlled by an amplifier 23, also disposed in the eyepiece 16, intended to vary its light intensity. For each predetermined measurement frequency, the analog sinusoidal signal emitted by the generator 21 is transformed into a digital sinusoidal signal modulated in sigma-delta modulation by a modulator 24. The use of sigma-delta modulation makes it possible to obtain, on the one hand, great speed of measurement, good precision and great reliability of the signal displayed and, on the other hand, true linearity over the entire modulation range, since this modulation technique makes it possible to get around the related problems well to the non-linearity of the diode 22. The modulated signal is sent to the eye of the person, against which the eyepiece 16 is applied, by means of transmission means 17 which, in the example illustrated, is consist of electrical cables housed in a flexible sheath.

In an alternative embodiment, the light source 22 can be replaced by a source 32 as shown in FIGS. 3A and 3B. This light source is formed by ten light-emitting diodes 33 regularly arranged at the periphery of a hemisphere 34 and indirectly emitting white light for the eye. The center of this hemisphere is located on the optical axis of the eye to be checked 35. The light emitted by these diodes 33 is reflected by the bottom of the hemisphere so as to converge towards the eye 35 and form a source uniform bright. This embodiment of the light source makes it possible to reduce the effort which the eye must make when it must focus only on one point.

The strategic measurement unit 20 is further arranged to receive the information transmitted by the person using the push-button 13 and to transmit this information to a storage memory 25 which is advantageously a read-only memory of the EPROM type. When the measurement cycle is finished, the content of the memory 25, that is to say the different values of the limit modulation of the transmitted signal determined by the person when it no longer sees the blinking, is transferred to a calculation unit 26 intended to analyze the information received and to transform it into information that can be displayed by means of the diodes 14.

To obtain a device of small dimensions and a low cost price, the strategic unit 20, the signal generator 21, the modulator 24, the read-only memory 25 as well as the calculation unit 26 are combined in a microprocessor single 27. However, provision can also be made to gather these elements on two different microprocessors, one grouping together the strategic unit 20 and the elements linked to it, and the other relating only to the calculation unit 26.

The purpose of the measuring device 10 is to capture the characteristic of the eye in a minimum time not to exceed two minutes because, after this time, the eye gets tired. To do this, it operates automatically without the help of an operator and its operating strategy is based on the method according to the invention in which the threshold of perception of the twinkling of the eye is measured for approximately ten predetermined and defined frequencies. between 7 and 50 Hz.

The measurement cycle takes place as follows, the device being switched on and the eyecup applied against the eye to be checked. We start the measurement at 7Hz with a 100% modulation and the modulation is reduced linearly, on a logarithmic scale, step by step, until the person no longer perceives the blinking, which he signals by actuation push-button 13. The strategic unit then switches to a higher frequency and so on until the person no longer perceives blinking, even at 100% modulation. However, to speed up the measurement process, at this new frequency, we no longer start with the maximum modulation but with a lower modulation chosen in such a way that the person still perceives a blinking. This is achieved by choosing a starting modulation which is calculated from the modulation determined at the previous frequency. The value of the modulation increase jump was chosen from statistics. However, if during the measurement at a certain frequency, the modulation jump is too small and the person does not perceive blinking, the device then crosses the whole range of modulations and repeats the measurement at the same frequency with a rate maximum modulation.

When the whole range of predetermined frequencies has been scanned and the strategic unit has thus determined the flicker limit of the person, the limit / frequency modulation function, which has been established, is processed by the calculation unit 26. This unit will then undertake, with the values obtained, a mathematical non-linear regression operation on the difference between a reference transfer function and the flicker limit function measured and defined by G (f) = log af

(1+ (f / fι) ³ ). (1+ (f / f ₂ ) ³ ) f being the applied frequency, a being a coefficient linked to the retina, fi being the cut-off frequency of the optic nerve, and f ₂ being the cut-off frequency of the brain.

This operation will make it possible to quantitatively determine the parameters a, fi and f ₂ , as well as the ratio k which is the ratio between the cut-off frequency of the brain f _{2 and} that of the optic nerve fi and which thus characterizes the progression of the disease. To obtain optimal reliability, in this calculation, during the summation, the extreme measures are eliminated _.

A ratio greater than 1 indicates an alteration of the optic nerve. This information is transmitted to the person via the engagement of a diode 14. For example, to indicate that the eye is good and that k is substantially equal to 1, a green diode will light up . Otherwise, if k is clearly greater than 1, a red diode will light up. It is it is possible to provide several diodes for each color in order to indicate more precisely the state of the eye.

By design, this device is compact and low cost. It can thus be used in any environment and by any person wishing to carry out a control, since it works automatically.

It is possible, within the framework of the procedures, to perform the frequency sweep from 50 Hz to 7 Hz and we can imagine a procedure where we go from non-flickering to flickering to obtain the limit threshold of perception of the eye. Other means of displaying the result of the measurements can also be provided. In an alternative embodiment, the light source can be integrated into the housing 11, the eyelet 16 then being arranged on one of the lateral faces of the housing. In another variant, the eyecup may contain an optical system arranged in front of the diode in order to ensure a Maxwellian view.

Claims

1. Apparatus for detecting a disease of the retina or of the optic nerve of the eye of a person, in particular glaucoma, comprising a modulated light source (22) for measuring the threshold of perception of flickering of the eye to different predetermined frequencies of said light source, by determining a deLange curve relating to this eye for these frequencies, a strategic unit of measurement associated with means for generating and varying the frequency and modulation of the light emitted, means for transmitting this light modulated towards the eye of the person to be examined, means for analyzing the signals emitted by the eye as a function of the light signal received and for transforming them into a final value defining the degree of progress of the affection and being able to be displayed, and means for displaying this final value, characterized in that the strategic measurement unit (20) is arranged to obtain said curve so automatic, in that the apparatus comprises means arranged to compare the curve obtained and a reference curve and determine, for each frequency, the ratio (l <) existing between the frequency (f ₂ ), corresponding to the cut-off frequency of the signal from the person's brain in response to the perception of the end of the flashing of the light signal emitted, and the frequency (fi), corresponding to the cutoff frequency of the signal from the optic nerve of this person in response to the perception of the end of the flashing of this same light signal emitted, and in that the means for analyzing the emitted signals comprises a calculation unit (26) arranged to sum the values of (k) obtained for all the frequencies and to obtain, so automatic, said final value of (k).

2. Apparatus according to claim 1, characterized in that it comprises means arranged so that, at each frequency, the modulation of light decreases linearly, on a logarithmic scale, from 100% to 0.2% with a linearity factor equal to 0.8.

3. Apparatus according to claim 1, characterized in that the means for generating and varying the frequency are arranged to generate a linear series of frequencies, on a logarithmic scale, located between 7Hz and 50 Hz with a linearity factor equal to 1 25.

4. Apparatus according to claim 1, characterized in that it comprises a generator (21) of analog sinusoidal signals.

5. Apparatus according to claims 1 and 4, characterized in that the means for varying the modulation of the light emitted comprise a modulator (24) arranged to transform the analog sinusoidal signals into digital sinusoidal signals in sigma-delta modulation.

6. Apparatus according to claim 1, characterized in that it comprises a memory (25) arranged to store, during the measurement process, the different values of the limit modulation of the light signal emitted.

7. Apparatus according to claim 1, characterized in that the calculation unit (26) comprises means for calculating a non-linear regression. -

8. Apparatus according to claims 1, 4, 5 and 6, characterized in that the strategic measurement unit (20) associated with the generator (21), the modulator (24) and the memory (25), as well as the 'computing unit (26) are made in the form of a single microprocessor (27).

9. Apparatus according to claims 1, 4 5 and 6, characterized in that the strategic measurement unit (20) associated with the generator (21), the modulator (24) and the memory (25), on the one hand , and the computing unit (26), on the other hand, are made in the form of separate microprocessors.

10. Apparatus according to claim 1, characterized in that the light source is at least one light emitting diode (22) emitting white light associated with a current amplifier (23).

11. Apparatus according to claim 1, characterized in that the means for displaying the final value of (l <) comprise at least two light-emitting diodes (14) whose emission color is linked to said final value of the ratio ( l) calculated.

12. Apparatus according to claim 1, characterized in that it comprises means (13) arranged so that, at each frequency, the person communicates to the strategic measurement unit (20) the end of the perception of the flashing of the signal light emitted.