Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – For fusion and space perception testing
Reexamination Certificate
2000-09-11
2001-08-28
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
For fusion and space perception testing
Reexamination Certificate
active
06280032
ABSTRACT:
The invention relates to a new method for determining the spectral sensitivity curve of the human vision system, to a new method for correcting color vision deficiencies and to respective apparatus for carrying out the methods, i.e. to color sensitivity measuring and correcting systems. The correcting system includes color glasses and lenses, as well as circuits by which the color image of a color display can be influenced to compensate the color vision deficiencies of a particular subject.
Color vision deficiencies are the result of non-uniform sensitivities of the different pigmented cones in the eyes of the subject; in other words such persons have spectral sensitivity curves differing from the standard curve characteristic of those with normal vision capabilities. There are certain diseases or disorders, wherein one or more pigmented types of cones are missing. Such persons are color blind, and physical devices cannot correct such deficiencies. As long as the subject has more than two types of cones with differing spectral sensitivities, color vision deficiencies can be corrected or compensated. A few percentages of color vision deficiencies have acquired nature, i.e. they are the result of certain diseases, and they can disappear when the basic disease is cured. It is often important for the practitioner to make distinction between inborn and acquired color vision deficiencies.
Different statistics report differing incidence rate for color deficiencies, and according to data reported in the 1996 edition of Encyclopaedia Britannica this rate is about 4% for men and 0.4% for women. If lighter (undetected) color vision problems are also taken into account, the actual occurrence rate is probably higher.
There are several empirical methods for determining color vision deficiencies, of which the most common one is the use of color tables comprising mosaic structures of color spots, i.e. pseudo isochromatic figures, which are chosen in such a way that a pattern is hidden therein. With normal vision the embedded patterns can well be recognised. The color structure is arranged in such a way that in case of most kinds of color vision deficiencies the subject under test cannot identify the embedded pattern in case of one or more specific tables. The practitioner can determine the fact and the type of color deficiencies based on the result of such tests. An example for such tables is the book of Karl Verhagen and Dieter Broschmann: “Tafeln und Prüfung des Farbensichtes” published by Georg Thieme Verlag, 1992 and its Hungarian translation by Medicina Kiadó, Budapest, 1992. The tests based on such tables should be carried out so that natural light should evenly illuminate the page under test and the light flux should be at least about 40-50 lux.
While this is the most widely used method for the detection of color vision deficiencies, it is inappropriate to detect color deficiencies caused by the sensitivity errors in the blue spectral range. Color tables cannot discover smaller problems in the color vision system as long as the subject is capable of recognizing the embedded pattern.
Color vision properties have been thoroughly analyzed by George Wald “The Receptors of Human Color Vision” and the appendix thereto by W. S. Stiles (Science, Vol. 145, September 1964, pp. 1007-1016). Wald has worked out a method for measuring the spectral sensitivity curves and reported his results of measurement. In addition he compared his results with the results of other researchers and compiled sensitivity curves of different origin for the most typical color vision deficiency types. It is beyond doubt that color vision deficiencies are truly reflected in the specific spectral sensitivity curve of the subject.
The exact mechanism of color vision is not yet known. In a model the color vision system is thought that cones have three different pigment types, and color vision is obtained by the processing of this information in the vision center of the brain. This theory cannot explain certain duality of the color vision deficiencies, i.e. where deficiencies are experienced in pairs of different colors i.e. red-green or blue-yellow. In the most advanced theory color vision is thought to be the result of two curves each including positive and negative chromatic values (Hurvich and Jameson, 1972). It is not the task of this specification to provide full theoretic background for color vision, but to focus the attention to the significance of the measurement of spectral sensitivity curves.
The methods of Wald and other authors for measuring the spectral sensitivity have not obtained wide acceptance, since they require long time and expensive instrumentation, furthermore apart from the scientific value; the knowledge of such curves has not served as basis for any practical therapeutic application.
Several authors have recognised that color vision deficiencies can be corrected by the use of color filters of specific spectral distribution. Hungarian patent 108.453 of Abraham et al. is based on the three-receptor theory and suggests that color vision deficiencies are the result of shifts in the respective spectral sensitivity curves. They determine the respective curves, provide the function of the deviations from the standard curves and apply combined filters that compensate for such shifts. The specification does not give a clear teaching how can the deviation function be established and how should the filter be made.
The primary object of the invention is to provide a new method for determining the spectral sensitivity curve of the human vision system in a fast and simple but reproducible way.
A further object of the present invention is to establish a color light which has a specific spectral distribution (i.e. color) capable of compensating the difference between the specific spectral sensitivity curve of a subject and the standard sensitivity curve associated with normal color vision.
A still further object is to provide an apparatus by which such sensitivity curves can be determined and which can provide the aforementioned compensating light.
It is also the object of the invention to provide a specific glass, which uses the compensating color as a filter and can provide thereby a normal color vision for the subject.
The last object of the invention is to provide a compensating system usable in a color display, that modifies the colors to be displayed in such a way that the subject with a specific color vision deficiency can see the picture with correct colors as if he had no deficiency.
According to the invention it has been recognised that the spectral sensitivity curve can be obtained by utilising a law known in a different field of the physiology of sensory reception i.e. the Ferry-Porter law. This law relates to a phenomenon called flicker, which is the sensation evoked when a visual stimulus is repeated rapidly. At low repetition rates the fluctuation can well be sensed, at higher rates the sensation becomes one of flicker - i.e., rapid fluctuations in brightness; finally, at a certain speed, called the critical fusion frequency, the sensation becomes continuous and the subject is unaware of the alterations in the illumination. At high levels of luminance, when cone vision is employed, the fusion frequency is high; increasing with increasing luminance in a logarithmic fashion and this is the Ferry-Porter law. From the above-cited paper of Wald it is known that the sensation of luminous intensity is a logarithmic function of the illumination. From the Ferry-Porter law the critical fusion frequency is a logarithmic function of luminance, thus under specific conditions it can be attained that the visual sensation will be a linear function of the critical fusion frequency.
The way of obtaining the spectral sensitivity curve of the vision of a subject by means of determining the critical fusion frequency at predetermined discrete spectral wavelengths will be called critical fusion frequency scanning or CFFS method, and this forms the basic concept of the present invention.
The predetermined discrete frequen
Kelemen Gabor J.
Manuel George
Venable
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