What is contrast sensitivity?

In standard vision testing, an eye chart is viewed in high contrast conditions, where black letters or numbers of varying sizes are sharply displayed against well-lit, white backgrounds. The real world, however, is full of shades of grey in which those people hampered by poor contrast sensitivity can have serious problems seeing distinct images under certain conditions.

Even if you have 20/20 vision, you may have poor contrast sensitivity. Contrast sensitivity testing is important because it allows Optometrists to determine how well you function in real-world conditions, where objects may "blend" and become indistinguishable in backgrounds with similar colouring. In addition this measurement gives a more realistic assessment of sports related acuity.

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Symptoms of low contrast sensitivity

Do you have problems with night driving, including inability to see traffic lights or spot other cars and pedestrians. Do you require extra light to read, and do your eyes become tired when you read or watch television? Do you stumble when you fail to see that you need to step down from a curb onto similarly coloured pavement?

Low contrast sensitivity also can be a symptom of certain eye conditions or diseases such as cataracts, glaucoma, or diabetic retinopathy.

Contrast sensitivity testing

Contrast sensitivity testing gauges your ability to see objects in terms of size and contrast. Small objects, for example, can be seen only when their contrast is very high. Medium-sized and large objects, on the other hand, often can be seen when their contrast is low. When you undergo a contrast sensitivity test, you may be shown images such as dots and bars with different contrasting backgrounds under varying conditions such as glare. The Vector Vision testing equipment has become the worldwide benchmark for standardised contrast sensitivity testing.

A person with low contrast sensitivity might see a scene in this way (top), with very little distinction of boundaries in the objects shown. Note how much contrast this scene has lost compared with the image depicting normal sight.

contrast sensitivity testing