Tritanomaly

Tritanomaly is a form of anomalous trichromacy involving the S-cones, which are responsible for detecting short-wavelength (blue-violet) light. In tritanomaly, the S-cones are present but their opsin protein has an altered spectral response, leading to reduced discrimination along the blue-yellow axis. All three cone types still function, so people with tritanomaly retain trichromatic vision, but with a compressed ability to distinguish blues from greens and yellows from reds. It is the rarest of the six main types of anomalous color vision.

The visual effect of tritanomaly is generally subtle. Blues may appear slightly greener or more washed out than normal, and yellows may look slightly pinkish or orangish. The confusion axis runs between blue and yellow, as opposed to the red-green axis affected in the more common protan and deutan conditions. Because S-cones contribute relatively little to overall brightness perception, tritanomaly does not cause noticeable luminosity changes. Many people with mild tritanomaly may be unaware of any color perception differences.

Hereditary tritanomaly is caused by mutations in the OPN1SW gene on chromosome 7 that shift the S-cone opsin's spectral sensitivity without completely eliminating its function. The condition is autosomal, meaning it is not linked to the X or Y chromosome and affects all sexes equally. Acquired tritan-type deficiency is actually more common than the inherited form and can result from cataracts (yellowing of the lens), glaucoma, macular degeneration, diabetic retinopathy, or exposure to certain medications and chemicals. Distinguishing inherited from acquired tritanomaly requires careful clinical evaluation.

Tritanomaly is not detected by standard Ishihara color plate tests, which are designed for red-green deficiency. Tritan-specific tests include the HRR (Hardy-Rand-Rittler) pseudoisochromatic plates, the Farnsworth D-15 arrangement test, and computerized color vision assessments like the Cambridge Colour Test. Because tritanomaly is so rare as an inherited condition, a positive tritan result should prompt a comprehensive eye examination to rule out acquired causes. Anomaloscopy specific to the tritan axis is technically possible but rarely available in routine clinical settings.

Tritanomaly is typically the least impactful of the color vision deficiencies in terms of daily functioning. Most safety-critical color systems, such as traffic lights and warning signals, use red and green rather than blue and yellow, minimizing safety concerns. The biggest practical challenges tend to arise in artistic, design, and scientific fields where precise blue-green or blue-purple discrimination is needed. Digital accessibility tools and color-blind display modes can help in these contexts. Because it is so rare, people with tritanomaly may find limited peer support compared to those with red-green deficiency.

If you have difficulty distinguishing blues from greens or yellows from oranges, schedule a comprehensive eye exam that includes tritan-specific color vision testing. This is especially important if the difficulty is new or has worsened over time, as acquired tritan deficiency can be a sign of cataracts, glaucoma, or retinal disease that may benefit from treatment. For people diagnosed with inherited tritanomaly, routine monitoring every one to two years is recommended to ensure the condition remains stable and no additional eye health issues have developed.