Color Blind Test

About this test

The Ishihara test — designed by Dr Shinobu Ishihara in 1917 — uses plates of coloured dots that form a number visible to people with typical color vision. People with red–green color vision deficiency see a different number, or nothing at all.

What it screens for

• Protanopia / protanomaly — reduced or missing sensitivity to red light.
• Deuteranopia / deuteranomaly — reduced or missing sensitivity to green light.
• Together these account for the vast majority of color vision deficiencies (~8% of men, ~0.5% of women).

What it doesn't screen for

• Tritanopia (blue–yellow deficiency) — very rare, and Ishihara plates are not designed to detect it.
• Achromatopsia (total color blindness) — requires clinical testing.
• Subtle acuity or contrast issues unrelated to color.

For the most reliable read

• Use a well-calibrated screen at full brightness.
• View in a normally-lit room — not direct sunlight or a fully dark room.
• Don't wear tinted glasses.
• Answer with your first instinct; don't strain.

Understanding colour vision deficiency

Colour vision deficiency — commonly called colour blindness — means seeing colours differently from most people, which usually makes it hard to tell certain colours apart.¹ It is far more common than most people assume: according to the U.S. National Eye Institute, red–green colour blindness affects roughly 8% of men and 0.5% of women of Northern European ancestry.² The vast majority of cases are inherited and present from birth, though colour vision can also change later in life through eye disease, brain or nervous-system conditions, or certain medicines.³

Why it mostly affects men

The genes for the most common, red–green form are carried on the X chromosome and are recessive. Males have a single X chromosome, so one affected copy is enough to produce the deficiency; females have two X chromosomes, so both copies must carry the gene — which is far less likely.³ That single difference in inheritance is why colour blindness shows up in men many times more often than in women.

The main types

The retina relies on three kinds of colour-sensing cone cell, tuned to long (red), medium (green), and short (blue) wavelengths. Colour vision deficiency happens when one type is missing or shifted in sensitivity:⁴

• Red–green (protan and deutan) — by far the most common group. Protanomaly and protanopia affect the red cones; deuteranomaly and deuteranopia affect the green cones. Deuteranomaly is the single most common type.
• Blue–yellow (tritan) — much rarer, affecting the blue cones, and it occurs about equally in men and women.
• Complete colour blindness (monochromacy / achromatopsia) — seeing no colour at all, which is rare and requires clinical testing.

How the Ishihara test works

The plates on this page follow the method published by Dr Shinobu Ishihara, a professor at the University of Tokyo, in 1917.⁵ Each plate is pseudoisochromatic: dots of varying size and brightness are coloured so that a figure — usually a number — stands out to people with typical colour vision but blends into the background for someone with a red–green deficiency (or the reverse). Because it is quick, needs no equipment beyond the printed or displayed plates, and is easy to score, the Ishihara test became a widely adopted international screening standard and remains one of the most recognised colour vision tests today.⁵

A screening tool, not a diagnosis

An online test like this one is a useful first check, but it cannot replace a professional eye exam. Screen calibration, brightness, ambient light, and even the device's colour profile all affect the result, and no self-test can grade the severity of a deficiency or rule out the rarer forms. There is currently no cure for inherited colour vision deficiency, though most people adapt well and may not need any treatment.⁴ If a result matters for a career with colour-critical requirements — aviation, rail, electrical work, or the armed forces, for example — or if colour vision seems to have changed recently, see an optometrist or ophthalmologist for formal testing.⁴

Sources

1. National Eye Institute (NIH). Color Blindness.
2. National Eye Institute (NIH). Types of Color Vision Deficiency.
3. National Eye Institute (NIH). Causes of Color Vision Deficiency.
4. NHS. Colour vision deficiency (colour blindness).
5. Wikipedia. Ishihara test.

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