Table I

Classification and Incidence of Color Vision Defects

Type % Males

Congenital

Trivariants (three cones present)

Normal 91.2 Anomalous

Protanomaly (L cone opsin abnormal) 1.3

Deuteranomaly (M cone opsin abnormal) 5

Tritanomaly (S cone opsin abnormal) 0.001 Divariants (Two cones present)

Protanopia (L cones absent) 1.3

Deuteranopia (M cones absent) 1.2

Tritanopia (S cones absent) 0.001 Achromats

Complete achromat (all cones absent) 0.00001

S cone achromat (L and M cones absent) 0.000001 Acquired

Tritanopia (outer or peripheral retinal disease) 0.01 Protan deuteranopia (inner or central retinal disease) 0.01

Cerebral achromatopsia (brain disease) 0.0000001

legally blind. A second form of achromatopsia is due to a gene defect on chromosome 2 for an ion channel exclusive to cones. These subjects only have functional rods.

In less severe defects, only an L or an M cone gene is functional. Such subjects have blue-yellow color vision obtained by comparing S cones with the remaining long-wave cone mechanism. Subjects who lack L cones are called protanopes. They are insensitive to the long wave end of the spectrum (the red end). Subjects who lack M cones are called deuteranopes. They are sensitive to the entire spectrum. Both protanopes and deuteranopes cannot distinguish reds from greens and have only blue-yellow color vision. They all have high spatial resolution.

In milder defects, both L and M cone opsins are transcribed but the absorption spectrum of one is shifted closer to the other, diminishing the potential for chromatic contrast. Such subjects are called deuter-anomalous if the M cone opsin is abnormal and protanomalous if the L cone opsin is abnormal. They have reduced red-green but normal blue-yellow color vision. They all have high spatial resolution. The similarities of colors vary in different ways for each color deficiency (Fig. 13).

Similar to Normals

I- Similar to Deuteranopes

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