Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1991-11-26
1993-08-17
Bovernick, Rodney B.
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
351243, A61B 310, A61B 302
Patent
active
052373495
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a papillometer comprising a flashing luminous source, an optical device for transmitting the light emitted by this source to the eye to be examined, an electronic control device to vary the frequency at which the source flashes and means for measuring eye flickering.
Various types of papillometers, which are devices for measuring the eye's response to the flashing of a light source, are already known. Flickering may be defined as the eye's perception of flashing from a light source. When a light source is made to flash at low frequency with 100% modulation, the eye distinctly perceives the light alternately going on and off. When the flashing frequency of the source increases to a value of the order of 40 Hz, the eye no longer perceives the flashing clearly and the patient's physiological impression is that the light is more intense than it actually is. At an even higher frequency, flickering disappears and gives way to the impression that the light is being continuously emitted. The patient has reached what is known as the fusion threshold, currently called CFF (Critical Flickering Frequency).
If a fixed frequency is maintained and modulation is decreased, the same phenomenon is observed. This phenomenon has been studied by DE LANGE, who proposed submitting the eye to sinusoidal stimulation conforming to the mathematical formula:
Frequency f and modulation m may vary independently. The limits for modulation variation are from 0 to 100%, given that it is impossible to create a negative light.
This stimulation makes it possible to plot curves representing the fusion threshold as a function of the frequency and modulation for each eye examined. The general form of these curves is shown in FIG. 2, in which the abscissa shows the logarithm of frequency in Hertz and the ordinate, the logarithm of the inverse of modulation as a percent.
DE LANGE'S curves have three principal applications: animation projected on a screen, DE LANGE's curves must be taken into account to prevent the viewer's eyes from flickering; and particularly the detailed analysis of the small sudden deviations in the curve, aids understanding the information transmission mechanisms inside the retina, especially color perception; diagnosis of an eye and provides information about the patient's other illnesses or intoxication. Therefore, the papillometer may become a non-invasive diagnostic instrument of general interest, rather than being limited to ophthamological use.
A first mechanical apparatus using polarized filters, rather bulky and costly, was commercialized by the METABO company in Switzerland.
To make this device function independently, use of analog electronics and a light source consisting of light-emitting diodes was attempted. However, these attempts were shown to be relatively inconclusive due to lack of precision and the instability of the light sources over time.
The present invention proposes overcoming the disadvantages described above by achieving a reliably performing papillometer which is nevertheless compact and light.
This goal is achieved by the papillometer according to the invention, characterized in that the control device is designed to generate a numerical sinusoidal signal in delta modulation.
According to a preferred embodiment, the flashing light source is a light-emitting diode.
Preferably the electrical energy source, the light-emitting diode, the optical system for focalizing the light emitted by the source onto the retina of the eye to be examined and the control device are all contained within the same housing.
The electronic control device preferably has a memory in which at least one range of frequencies and at least one range of modulations are stored.
According to a preferred embodiment, the memory system may comprise several storage devices, each corresponding to a range of frequencies, with the stored data defining the control signals for the light source.
The present invention will be better understood with reference to the description of a preferred embodiment and to t
REFERENCES:
patent: 4142184 (1979-02-01), Lake
patent: 4500844 (1985-02-01), Lisco
patent: 4567883 (1986-02-01), Langer et al.
Review of Scientific Instruments vol. 51, No. 10, Oct. 1980, New York U.S. pp. 1396-1402; R. E. Gander et al.: "Precise stimulus for the measurement of visual flicker sensitivity" see whole document.
NHK Laboratories Note No. 198, Mar. 1976 Tokyo JP pp. 2-10 Akira Watanabe et al.: "Chromatic spatial sine-wave responses of the human visual system" see whole document.
Bovernick Rodney B.
Ciposa Microtechniques S.A.
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