Tritan Test

What is tritan color blindness?

Tritan deficiency involves the S-cone, the photoreceptor tuned to short-wavelength light. It comes in two forms: tritanomaly, where the S-cone pigment is shifted, and tritanopia, where the S-cone is absent. Either way the blue-yellow axis loses contrast, so blue and green start to look alike, yellow washes out toward pale pink or white, and violet reads as a plain grey-blue.

It is genuinely rare — under 0.01% of people — and unlike red-green deficiency it affects men and women about equally, because the S-cone gene sits on chromosome 7 rather than on the X chromosome. It is also the axis most often affected by acquired causes: cataract, glaucoma, diabetic retinopathy, macular degeneration and some medications all tend to hit blue-yellow first.

That combination is why a tritan result deserves more caution than a red-green one. Inherited tritan deficiency is unusual; blue-yellow trouble that has appeared or worsened over time is a reason to see an eye-care professional rather than to accept a screening result.

Why the Ishihara test misses tritan deficiency

Ishihara plates were designed for red-green screening, and their colour pairs sit along the protan and deutan confusion lines. Nothing in the standard set challenges the blue-yellow axis, so a person with tritanopia reads the plates correctly and passes. That is not a flaw in the test — it is what the test is for — but it is the reason a tritan deficiency so often goes unnoticed.

Detecting blue-yellow properly needs either plates designed for it, such as the HRR set, or an arrangement test like the Farnsworth D-15, where a tritan confusion axis shows up clearly in the pattern of crossings. The screening on this page takes the first approach with generated plates on the blue-yellow line.

If you want the arrangement view as well, the D-15 on this site plots your axis directly, which is the most informative thing you can do about tritan short of a clinical exam.

How reliable is a tritan test on a screen?

Less reliable than red-green, and it is worth being blunt about why. Ordinary displays render short-wavelength blues least accurately, ambient light shifts blue perception more than it shifts red or green, and blue-light-reducing modes on phones and laptops distort exactly the axis being measured. All of that pushes toward false positives.

The test is tuned around that. The blue-yellow plates stay deliberately easier than the red-green ones, so someone with typical colour vision reliably passes them and only a genuine tritan deficiency — where blue-yellow discrimination is substantially reduced — fails. The trade-off is that a mild tritanomaly may pass. That is the right way round for a screening: better to miss a borderline case than to alarm people whose screen is simply rendering blue badly.

Before you start, turn off night mode and blue-light filters, set brightness to full, and work in moderate, neutral light. Those three things matter more on this axis than on any other.

Tritan test — frequently asked questions

What is a tritan test?

A screening for blue-yellow colour vision deficiency, which affects the eye's S-cone. It uses colour pairs along the blue-yellow confusion line, so only S-cone discrimination can separate the symbol from the background. Standard Ishihara plates do not test this axis at all.

Does the Ishihara test detect tritanopia?

No. Ishihara plates are built around the red-green confusion lines, so someone with tritanopia typically reads them correctly and passes. Blue-yellow deficiency needs plates designed for it, such as the HRR set, or an arrangement test like the Farnsworth D-15.

How common is tritan color blindness?

Rare — under 0.01% of people for the inherited form, and unlike red-green deficiency it affects men and women about equally, because the S-cone gene is on chromosome 7 rather than the X chromosome. Acquired blue-yellow changes from eye disease or medication are more common than the inherited form.

What colors do tritans confuse?

Blue with green, yellow with pale pink or white, violet with grey-blue, and red with orange-pink at the warm end. Teal is a classic problem colour because it sits right on the boundary.

Can a screen test tell me if I have tritanopia?

It can flag it, not confirm it. Displays render short-wavelength blues least accurately, ambient light shifts blue perception, and night-mode filters distort exactly this axis. Treat a tritan flag as a reason to book an eye exam rather than as a result — particularly if your blue-yellow vision has changed over time.

Is blue-yellow color blindness inherited or acquired?

Both occur, but acquired is the more common story. Inherited tritan deficiency is autosomal dominant and rare. Acquired blue-yellow change is associated with cataract, glaucoma, diabetic retinopathy, macular degeneration and certain medications, and typically develops or worsens over time rather than being lifelong.