Contrast sensitivity test

Letters get fainter step by step until you can't make them out. It takes a minute and shows how well you see in low contrast, such as dusk, fog, rain or night driving.

Why contrast matters as much as sharpness

A standard eye chart uses black letters on a bright white background, the easiest possible case. Real life is rarely like that. Faces in a dim room, a curb at dusk or a pedestrian in the rain all have low contrast. You can read 20/20 on a chart and still struggle with these.

This test works in the spirit of the Pelli-Robson chart that eye doctors use: the letters stay the same size, but their contrast halves at each step.

What can reduce contrast sensitivity?

Cataracts are the most common cause, and often reduce contrast before they affect sharpness. Glaucoma, diabetic eye disease, macular degeneration, dry eye and an out-of-date glasses prescription can all play a part. Contrast sensitivity also declines gradually with age.

How to take the test

Sit at a normal viewing distance with both eyes open and your usual glasses on. Turn the screen brightness up and switch off Night Shift, True Tone and blue-light filters, which change how faint the letters look. Avoid glare from windows or lamps on the screen.

Frequently asked questions

What is a normal contrast sensitivity score?

Most adults with healthy eyes can read letters down to a few percent contrast. If you lose the letters noticeably earlier than that, or have trouble driving at night, an eye exam is worthwhile.

Is trouble seeing at night a sign of cataracts?

It can be. Glare, halos around lights and washed-out colors are common early signs of cataracts. They can also come from other causes, so get it checked rather than guessing.

Does screen brightness affect the result?

Yes. A dim screen or a color filter makes faint letters harder to see. Use full brightness and turn off Night Shift or True Tone for the most reliable result.

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This is a screening tool, not a diagnosis. If you have sudden vision loss, flashes, a curtain over your vision, eye pain or new double vision, get urgent care now.