Tritanopia: Blue-Yellow Colour Blindness

Tritanopia is a rare form of colour vision deficiency caused by the complete absence of S-cones (short-wavelength sensitive / blue-sensitive cone cells). Unlike red-green CVD, tritanopia is not X-linked — it affects men and women equally and is inherited in an autosomal dominant pattern.

Key Facts

Prevalence: Approximately 0.008% of the population (affects men and women equally)
Cause: Absence or dysfunction of S-cones; autosomal (chromosome 7), not X-linked
Inheritance: Autosomal dominant in the congenital form; can also be acquired
Confusion axis: Blue-yellow axis (blue/green confusion; yellow/violet confusion)

How Tritanopia Affects Vision

With L-cones and M-cones intact but S-cones absent, tritanopes have difficulty with the blue-yellow axis of colour:

Blue and green appear similar — both may look greenish or teal
Yellow and violet are confused — yellow may appear pale or pinkish
Dark blue and black are confused
The red-green axis remains largely intact (unlike red-green CVD)

The visible colour experience is shifted toward a reduced ability to distinguish shorter wavelengths, while perception of the red-green spectrum remains relatively normal.

Congenital vs. Acquired Tritanopia

Congenital tritanopia is caused by mutations in the OPN1SW gene on chromosome 7. It is present from birth, stable throughout life, and follows an autosomal dominant inheritance pattern.

Acquired tritanopia can develop later in life and is associated with:

Glaucoma (most common cause of acquired tritan deficiency)
Macular degeneration
Diabetic retinopathy
Ageing (the lens yellows, reducing blue light transmission)
Certain medications including digoxin

Acquired tritanopia may be progressive and can affect one eye before the other.

Diagnosis

Tritanopia is often missed by standard Ishihara testing (which screens only for red-green CVD). Detection requires:

Farnsworth-Munsell 100 Hue Test — errors cluster along the tritan confusion axis (~45°–225° on the polar chart)
Farnsworth D-15 Test — tritan transpositions appear across the blue-yellow axis
Specialized tritan plates — Ishihara-style plates designed for tritan detection

Our Farnsworth test can indicate a tritan confusion pattern from the axis of errors in the polar chart.

Frequently Asked Questions

Is tritanopia as common as red-green colour blindness? No — tritanopia is far rarer, affecting less than 0.01% of the population. Red-green CVD affects approximately 8% of men.

Can women get tritanopia? Yes. Because tritanopia is autosomal (not X-linked), it affects men and women at equal rates. This is unlike red-green CVD, which is much more common in men.

Can tritanopia be corrected with glasses? There are no widely available corrective lenses for tritanopia equivalent to those for red-green CVD. Research is ongoing.