protanopiadeuteranopia

Protanopiadeuteranopia is a rare form of congenital color vision deficiency in which both long-wavelength (L) and medium-wavelength (M) cone photopigments are absent or nonfunctional in the retina, leaving the short-wavelength (S) cones as the sole functional photoreceptors for color perception. This leads to severe red-green color vision deficiency; in many cases the residual color discrimination resembles blue-yellow discrimination or is limited to blue hues. In clinical practice, the condition is frequently described as blue cone monochromacy when L- and M-cone function is absent and only S-cones remain, although some sources reserve the term “blue cone monochromacy” for a distinct genetic disorder with additional retinal changes. Because protanopia and deuteranopia are typically inherited as X-linked traits affecting males more often, a combined loss is extremely rare. Some cases may result from rearrangements or defective opsin genes (OPN1LW and OPN1MW) on the X chromosome.

Symptoms include difficulty distinguishing reds and greens, reduced visual acuity, and photophobia in some individuals. Diagnosis involves standard color vision testing, such as Ishihara plates, plus comprehensive anomaloscopy or hue discrimination tests to confirm the loss of L- and M-cone function; genetic testing may identify opsin gene alterations.

There is no cure. Management focuses on counseling and practical supports, with some individuals benefiting from tinted lenses to improve comfort or contrast. The condition is lifelong and stable.

See also: color vision deficiency, protanopia, deuteranopia, tritanopia, blue cone monochromacy, achromatopsia.