PubMed · 14487970
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C POPP. 1962. [On the Benham disk].. https://pubmed.ncbi.nlm.nih.gov/14487970/
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The normal X-chromosome-linked color vision gene array is composed of a single red pigment gene followed by one or more green pigment genes. The high degree of homology between these genes predisposed them to unequal recombination, leading to gene deletions or the formation of red-green hybrid genes that explain the majority of the common red-green color vision deficiencies. Gene expression studies suggest that only the two most proximal genes of the array are expressed in the retina. The severity of the color vision defect is roughly related to the difference in absorption maxima of the photopigments encoded by the first two genes of the array. A single amino acid polymorphism (Ser180Ala) in the red pigment accounts for the subtle difference in normal color vision and influences the severity of color vision deficiency. Blue cone monochromacy is a rare disorder that involves absence of red and green cone function. It is caused either by deletion of a critical region that regulates expression of the red/green gene array, or by mutations that inactivate the red and green pigment genes. Total color blindness is another rare disease that involves complete absence of all cone function. A number of mutations in the genes encoding the cone-specific alpha- and beta-subunits of the cation channel and the alpha-subunit of transducin have been implicated in this disorder.
This review gives a summary of all colour vision disorders (dyschromatopsias) and diagnostic methods and tests. Colour vision is inadequately treated in current literature with regard to the choice of diagnostic methods and the interpretation of results for a single disorder, which contributes to wrong dyschromatopsia diagnosing seen every day in specialist practice. Examination for colour disorders is usually outpatient and is carried out by ophthalmology or neurology departments or occupational health services under the supervision of an ophthalmologist to prevent misinterpretation of results and wrong occupational choices. The problem is very serious, and proper education should be able to provide guidelines for correct and early diagnosis of dyschromatopsia. As the examination is not well defined, it is very important to set unique criteria in diagnosing any single colour vision disorder.
BACKGROUND: The quantitative capability of the visual system can be tested using graphic presentations with defined size, form and colour. For presentations a chart projector or personal computer (PC) can be used. In the meantime the number of visual function tests on the internet is continually increasing. These tests are potentially available for over 400 million internet users with different hard- and software requirements. METHODS: From 38 on-line visual acuity tests and 19 on-line colour vision tests found by means of search engines on german language web pages, the offerer of the test, the type of chart used and the data for the test conditions, as well as hard- and software adjustment were registered. RESULTS. Various visual function tests, such as visual acuity tests, the Amsler grid, stereo and colour vision tests, can already be planned via internet. The variability of the tests ranges from a simple presentation of graphic elements to a laboriously programmed interactive input by the user to specify the test result. Most of the tests are presented by opticians and the optical industry. DISCUSSION: The analysed tests allow for a considerable variability of the test conditions, for example by missing data concerning the room lighting and lacking monitor calibration. Furthermore, problems of the web-based colour presentation were not considered or not considered sufficiently in most of the on-line colour tests. CONCLUSIONS: Because of the test deficits determined, the results of visual function tests on the internet are to be classified as doubtful. At present, most data of test offerers are not sufficient with respect to the test conditions. Standards should be defined for internet-based visual function tests and further studies should be followed to check the effectiveness of these tests for screening examinations.