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Table 2. Adapted from American Academy of Ophthalmology, 1995.

COLOR VISION TESTS

Test

Sensitivity/ Quantification

Ease of Administration

AO-HRR

Will miss very mild R-G/good classification

Excellent for all ages

Farnsworth-Munsell 100 hue

Extremely sensitive/ classify by error scoring

Tedious to administer

Ishihara

Extremely sensitive/ nil

Difficult for preschool children and low-IQ patients

Farnsworth's Panel D-15

Will only detect severe anomalous trichromats and dichromats/good classification

Easy to administer

Nagel's anomaloscope

Very sensitive/classify by anomaly (R-G) quotient

Good

Sloan's achromatopsia test

Grossly sensitive/ very incomplete achromatopsia pass

Easy to administer

NOTE: All tests, with exception of Nagel's anomaloscope, are to be administered under an illuminant C source such as provided by Macbeth easel lamp.

ocular pathology. A common cause of acquired color-vision loss is optic nerve disease, such as optic neuritis.

Inherited color blindness usually results from the loss of one of the photopigments and reduces color vision to two dimensions, or dichromacy. Other less common conditions reduce color vision to one dimension (mono-chromacy), or may completely extinguish it (achromacy). Vision in this last circumstance is purely dependent on the rods, which function primarily in dim conditions and do not contribute to color vision.

The most common forms of hereditary color blindness are protanopia/ anomaly and deuteranopia/anomaly, both of which are caused by defects in the red (L) and green (M) cones. Also known as red-green color vision deficiencies, they typically demonstrate an X-linked recessive pedigree pattern. The incidence of X-linked color-vision defects varies between human populations of different racial origin, with some of the highest rates appearing in Europeans and some populations in India.

The incidence of these common forms of color blindness is much lower in females than in males because the defects are inherited as X-linked recessive traits. Males, who have only one X chromosome, are hemizygous (meaning that they have only one gene present for the trait) and they will always manifest a color vision deficiency if they inherit an abnormal gene from their mother. Females, on the other hand, have two X chromosomes, one inherited from each parent, so they will not usually show a complete manifestation of the typical color defect unless they are homozygous, though a partial manifestation of color blindness may be present in heterozygotic carriers. A variety of special tests are used to screen for these red-green color-vision defects. see also Inheritance Patterns; Mosaicism; Signal Transduction; X Chromosome.

Eric A. Postel

Bibliography

American Academy of Ophthalmology. Retina and Vitreous: Basic and Clinical Science Course. San Francisco: American Academy of Ophthalmology, 1995.

Benson, William E. "An Introduction to Color Vision." In Clinical Opthalmology, vol. 3,

T. D. Duane and E. A. Jaeger, eds. Philadelphia: Harper & Row, 1987. Connor, Michael, and Malcolm Ferguson-Smith. Essential Medical Genetics, 5th ed. Oxford U.K.: Blackwell Science, 1998.

Gegenfurtner, Karl R., and Lindsay T. Sharpe, eds. Color Vision: From Genes to Perception. Cambridge, U.K.: Cambridge University Press, 2001.

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