Testing of color vision complements the assessment of visual acuity. In optic nerve disease, particularly demyelinating optic neuritis, the degree of dyschromatopsia may be proportionately greater than the degree of Snellen visual acuity loss; in macular disease, visual acuity and color vision tend to decline to corresponding degrees. Thus, in an eye with 20/30 visual acuity but severe color loss, optic neuropathy would be a more likely cause than macular disease. Persistent dyschromatopsia is common even after recovery of visual acuity in optic neuropathy.
Color vision testing is performed separately for each eye to detect unilateral disease. Pseudoisochromatic color plate testing was designed to screen for congenital red-green color deficiencies but may miss many mild cases of acquired dyschromatopsia. It is, however, commonly used clinically as a gross test of color vision, because optic neuropathies often manifest prominent red-green defects. Asymmetric defects between the 2 eyes are more significant than mild bilateral loss, which often represents a congenital defect, particularly in males. The AO HRR (American Optical Hardy-Rand-Rittler) plates are designed to screen for tritan defects as well as red-green defects. Blue-yellow color defects may accompany macular disease but also are common in dominant optic atrophy and may be an early sign in glaucoma. Lanthony tritan plates may be used to detect blue-yellow defects but are less commonly available than pseudoisochromatic plates.
More detailed color testing using arrangement tests comprehensively characterizes a color vision defect and may help distinguish acquired from congenital abnormalities. The Farnsworth Panel D-15 test, which requires the patient to arrange 15 colored discs in order of hue and intensity, is a good basic test if performed under standardized lighting conditions. This test can be made more sensitive by desaturation of the color chips (Lanthony desaturated 15-hue test). The Farnsworth-Munsell 100-hue test is far more detailed and provides better discrimination, using 85 discs, although the large amount of time required for testing and scoring limits its use for routine clinical testing. A shortened version, using only 21 of the color chips in the set, may be effective for discriminating among optic neuropathies.
Color vision testing is discussed further and illustrated in BCSC Section 12, Retina and Vitreous.
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, ThompsonHS, StoneEM. Evaluation of a significantly shorter version of the Farnsworth-Munsell 100-hue test in patients with 3 different optic neuropathies.1997;17(1):1–6.