Patent ID: 12256992

DESCRIPTION OF EMBODIMENTS

With reference toFIG.1, one embodiment of the device according to the invention comprises a detector10, a display20controlled by a controller30and an analyzer40.

The detector10is capable of providing information on variations in pupil diameter of a subject placed in front of the display20. It may in particular be an eye tracker. An eye tracker (or oculometer) is an apparatus capable of measuring a certain number of parameters of an eye or the eyes of an individual, such as the position of the pupil of the right eye and/or the left eye, the pupil diameter of the right eye and/or the left eye, the direction of gaze, and/or the convergence and synchronism of the activities of the two eyes. In the application considered here, it will generally be possible to limit the information gathered to information on pupil diameter, which is recorded over time.

To make the measurements of the detector10more reliable, the device may also comprise a chin strap or another system for stabilizing the position of the head of the subject in front of the display20.

The measurements on a subject using the device according to the invention are typically carried out eye by eye. It is preferable to mask the unmeasured eye.

The display20is for example a screen onto which a predefined luminous pattern is projected. It may also be a liquid-crystal or light-emitting-diode display. In another example, the detector10and the display20form part of a pupillometer.

The controller30controls the display20so that the latter presents, to the subject, a luminous pattern comprising a plurality of spatially distributed regions. In each region, the luminance of the pattern is modulated to exhibit a frequency-domain characteristic set by the controller20. Each region may thus be associated with a respective modulation frequency. The subject is invited to direct their gaze toward a central point of the pattern.

The analyzer40receives the signal output from detector10, which is dependent on the pupil diameter of the subject. It analyzes the frequency content of the signal in the band of the modulation frequencies employed in the luminous pattern. This analysis for example uses a Fourier transform of the time-domain variations in pupil diameter. Other time-frequency transforms may of course be used.

It is expected a priori that the Fourier spectrum thus computed will comprise a peak at each modulation frequency employed in the luminous pattern, because variable illumination of a segment of the retina normally engenders corresponding fluctuations in pupil diameter. However, if the retina has a scotoma, the peak will be weakened in the Fourier spectrum at the frequency associated with the region of the pattern that illuminates the scotomatous area.

It will be noted that pupil diameter reacts to the stimulus of the luminous pattern reflexively. The test performed using the device does not require any cognitive involvement on the part of the subject. It is an objective test. The subject is simply expected to focus on the center of the motif.

The time taken to carry out the test may be quite short, typically about one minute, this allowing the detector to record a number of luminance oscillations sufficient to make the Fourier-transform computation fine enough. A time shorter than two minutes has the advantage of stressing the subject for a short time only.

In the luminous pattern, the band of the modulation frequencies is chosen to reflect commonly observed physiological responses. The band is generally located in a range of 0.1 to 10 Hz, and typically in a range of 0.5 to 5 Hz.

An example of the geometry of the luminous pattern displayed by display20is shown inFIG.2. Here, the pattern comprises a central region R1surrounded by peripheral regions R2-R9that are distributed in two layers in the radial direction. The regions R2-R5of the first radial layer occupy four angular sectors of 90° around the central region R1, while the regions R6-R9of the second radial layer occupy four angular sectors of 90° around the regions R2-R5.

In one particular case, the luminance modulation frequencies employed in regions R1to R9are as follows:region R1: modulation at 3.60 Hz;region R2: modulation at 3.25 Hz;region R3: modulation at 2.40 Hz;region R4: modulation at 1.25 Hz;region R5: modulation at 2.13 Hz;region R6: modulation at 1.75 Hz;region R7: modulation at 1.00 Hz;region R8: modulation at 2.75 Hz;region R9: modulation at 0.75 Hz.

It will be noted that among these nine modulation frequencies, the highest is the one associated with the central region R1corresponding to the fovea. It is preferable for the frequencies to be selected so that, as in this example, one of them is not a harmonic of any other.

FIG.3illustrates results obtained on a healthy eye of an individual, showing, in arbitrary units, the modulus (power) Piof the discrete Fourier transform of the signal of the detector as a function of frequency i, as computed by the analyzer40. As expected, therein a peak may be seen at the modulation frequency of each of the regions R1-R9. In the example shown, the modulation frequencies are such that none of them is a harmonic of another. Thus, the overlap between a first peak corresponding to the main modulation frequency of a first region and a second peak corresponding to a harmonic modulation frequency of a second region is avoided. Thus, each peak allows the pupillary response of the subject to the modulation of the luminance of a single given region of the luminous pattern to be qualified.

In addition, since the number of regions is lower than 10, each peak is clearly separated from adjacent peaks in the spectrum shown inFIG.3. The pupillary response of the subject to the modulation of the luminance of each region of the luminous pattern may thus be quantified, for example on the basis of the height or of the integral of the peaks.

FIG.4is another representation of the results obtained for the same eye. Here, the power has been normalized to make it easier to view and compare the powers at the various modulation frequencies. Viewing is easier with this format. In this particular example, the technique used for the normalization consists in obtaining the normalized power P′iat a frequency i of the discrete spectrum by dividing the power in the vicinity of the frequency i by those of the frequencies of a broader neighborhood, according to the formula:
P′i=(Pi−1+Pi+Pi+1)/[(Pi−4+Pi−3+Pi−2+Pi+2+Pi+3+Pi+4)/2]

Other normalization methods may be used, provided that they meet the normalization objective, i.e. make inter-frequency comparisons of the stimulated powers possible.

If an eye of a subject has a scotoma, at least one of the power peaks visible at the frequencies R1-R9is decreased. The frequency at which the decrease is observed provides information on the location of the scotoma on the retina.

Phase information, representing the delay between the variation in luminance and the pupillary response may be used to refine the results obtained by analyzing power Pior P′i.

The phase of the Fourier transform of the signal of the detector depends on the delay between the stimulation and the pupillary response, and therefore is a complementary variable allowing a scotoma to be detected. Specifically, a poor transmission of the retinal signal is expected to result in a larger phase shift in the response. By associating the regions R1-R9with different modulation (stimulation) frequencies, it is possible to identify regions that respond with an abnormal phase shift, indicative of a probable scotoma. A mixed variable, combining power and phase shift at modulation frequencies, is therefore apt to provide a better sensitivity with respect to detection of deficient areas of the retina.

The advantages of the frequency-domain pupil test performed using the device presented above include:absence of a subjective task;rapidity;objective measurement related to measurement of the pupil;ability to locate the defect on the retina.

This test is especially applicable to the screening and diagnosis of ophthalmological diseases (macular degeneration, glaucoma, etc.).

The embodiments described above are a simple illustration of the present invention. Various modifications may be made to them without departing from the scope of the appended claims.