tritanomaly

Tritanomaly is a rare form of color vision deficiency characterized by reduced sensitivity to short-wavelength (blue) light, resulting in difficulties distinguishing blue-yellow hues. In tritanomaly, the short-wavelength cone function is abnormal but not completely absent, so blue colors can still be perceived, albeit with diminished discriminability from greens and yellows. By contrast, tritanopia involves a complete loss of blue perception.

Causes and inheritance: Tritanomaly results from genetic variations affecting the S-cone photopigment (short-wavelength opsin, OPN1SW) in the retina. The condition is not X-linked and is typically inherited in an autosomal dominant pattern with incomplete penetrance, though some cases occur as sporadic mutations. It is one of the most rare forms of color vision deficiency.

Prevalence and presentation: Tritanomaly is far less common than red-green deficiencies. Individuals with tritanomaly may notice that blues look greener or that blue-yellow distinctions are blurred, particularly in certain lighting conditions. The severity is generally milder than tritanopia.

Diagnosis: Routine color vision screening tests such as Ishihara plates may be normal or only subtly abnormal in tritanomaly. Definitive assessment often requires specialized testing, including color-mifference tests (for example, the Farnsworth-Munsell 100 Hue test) or computerized tests (such as the Cambridge Color Test) and, when available, genetic testing of OPN1SW.

Management: There is no cure for tritanomaly. Management focuses on adaptation and safety, such as using color-labeling aids or contrast enhancements in environments where color cues are important. Some individuals may use tinted lenses, though evidence for broad benefit varies.