Contrast Sensitivity Test

By Murat Şahin · Updated November 11, 2026 · How we test

Sharpness is not the whole story

A normal eye chart, like the one in our eye test, measures how small a letter you can read at full black-on-white contrast. Daily life is rarely that clean. A pedestrian in dark clothes at dusk, a step of the same color as the floor, a face in shade or a road in fog are all large but low in contrast. Contrast sensitivity is how faint a difference in lightness you can still see. Two people with the same sharpness on a letter chart can differ a lot here.

How the test works

You see one large letter at a time on a white panel. Pick it from six letter buttons, or press I can't see a letter. Letter keys work too. The letters come from the Sloan set (C, D, H, K, N, O, R, S, V, Z), which clinical charts use because the ten letters are about equally easy to recognize.

The letter gets paler as you answer correctly. It is drawn in grey on white, so this test does not check color vision; the color blind test does that. Its contrast falls in steps of roughly 0.15 log units, the same step size as the Pelli-Robson chart. The levels are limited to the greys an ordinary 8-bit screen can show, so the test has 14 levels, from black (log CS 0.00) to the faintest grey your screen can draw (log CS 2.05). The score always uses the contrast that was really displayed, not a rounded target.

The order follows a staircase:

1. You start on level 1 (black). Each correct answer jumps two levels paler until your first miss.
2. After that, two correct answers in a row move you one level paler and each miss moves you one level darker.
3. The test ends after 6 changes of direction, after 30 letters, or when you read the faintest level twice in a row.

With six choices, guessing one letter right is easy, but guessing two in a row happens about once in 36 tries. That is why your score is the faintest level where you answered two letters correctly in a row.

Reading your score

Your result is shown in log contrast sensitivity (log CS). If the faintest letter you read has a contrast of 10%, your contrast sensitivity is 1/0.10 = 10, and log CS is 1.0. At 1% contrast it is 2.0. Higher is better. The card also shows that contrast as a percentage, the level you reached and how many letters you got right.

The text under your score sorts it into four plain bands:

• 2.05 (level 14): you read the faintest grey the screen can show, so the screen set the limit, not your eyes.
• 1.21 to 1.75: you read pale grey letters at low contrast.
• 0.59 to 1.06: you read mid-grey letters but the palest were hard.
• below 0.59: you needed dark, high-contrast letters.

The test does not compare you with a population average, because no published average exists for this screen version. Use your personal best and your history, saved in this browser, to compare your own results over time.

The Pelli-Robson chart

The best-known clinical contrast test is the chart described by Denis Pelli, John Robson and Arnold Wilkins in 1988. All its letters have the same large size, and they are arranged in groups of three. Each group is 0.15 log units fainter than the one before, from 0.00 down to 2.25 log units. The patient reads it at 1 m, and the score is based on the faintest group in which at least two of the three letters were read correctly. This test uses the same letter set and step size but shows one letter at a time and adapts to your answers. It is not a copy of the chart and its scores are not directly interchangeable with it.

What lowers contrast sensitivity

• Screen and room: low brightness, glare or reflections on the screen, a dirty screen. The white panel stays white in dark mode on purpose.
• Glasses: smudges and scratches scatter light and lower contrast more than they lower sharpness.
• Age: contrast sensitivity slowly declines in later life, partly because the lens becomes less clear.
• Eye conditions: cataract, glaucoma, macular disease, diabetic eye disease and inflammation of the optic nerve can all reduce contrast sensitivity, sometimes before letter-chart sharpness changes.

Limits and when to see an eye doctor

Screens are not calibrated and their grey steps are coarse at the faint end, so the test cannot measure above 2.05 log CS, and two screens can give different results. It uses both eyes together and an approximate viewing distance. Uneven blur in one direction is a different problem, which the astigmatism test looks for. It is not a medical test. See an eye care professional if faint objects, night driving, fog or stairs have become noticeably harder, if your vision looks washed out or hazy, or if one eye sees colors and contrast differently from the other.

More checks like this are collected on our vision tests page.

Sources

• Pelli, D. G., Robson, J. G., & Wilkins, A. J. (1988). The design of a new letter chart for measuring contrast sensitivity. Clinical Vision Sciences, 2(3), 187–199.

Frequently asked questions