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SECTION 9 – Retina

Chapter 62 – Color vision defects

Maureen Neitz,
Jay Neitz

Clinical background

Key symptoms and signs

“Normal” color vision refers to the form of trichromatic color vision shared by most humans. It is mediated by three types of retinal cone photoreceptors, designated long- (L), middle- (M), and short- (S) wavelength cones. Each cone type is maximally sensitive to a different region of the visible spectrum (Figure 62.1). The neural circuitry for color vision compares the outputs of the three cone types and generates neural signals that give rise to the percepts of six basic colors: blue, yellow, red, green, black, and white, and to their mixtures. Color vision defects can either be inherited as the consequence of gene defects that affect the function of one or more cone type, or they can be acquired secondary to disease or through exposure to neurotoxins. The hallmark feature of color vision defects is a reduction in the number of different colors that are seen as distinguishable …