Color Vision
Color Vision Abnormalities

Deuteranopia

The term �green-blindness� does not apply to this condition since green lights appear as bright to him as they do to the normal observer. However, like the protanope, the deuteranope perceives only one hue through the mid and long-wavelength part of the spectrum so red, orange, yellow, and green are readily confused.

Tritanopia

So-called �blue-blindness.� The tritanope perceives only two hues, red and green, in the spectrum and confuses yellow with white. This condition is so rare, only a few cases have been investigated.

Typical Achromasy

Also known as monochromasy, or achromatopsia, the conditions in this category are truly �total color blindness.� The defect is widely attributed to a complete absence or non-functioning of the retinal cones. It may be caused by:

• very poor visual acuity (usually about 20/200)
• nystagmus where the constant horizontal movement of the eye increases with attempted steady fixation
• central scotoma
• photophobia where bright lights are avoided and where recovery of vision is very slow after exposure
• poor pupillary response under lighted conditions, but when the eye is well-adapted to darkness, the speed of pupillary response is normal

Atypical Achromasy

This rare condition shows a complete absence of color perception without the other abnormalities that accompany typical achromasy.