Contrast Sensitivity Testing
We often undergo standard vision testing by viewing eye charts in high contrast conditions, where black letters or numbers of varying sizes are sharply displayed against well-lit, white backgrounds. But the real world is full of shades of gray in which people hampered by poor contrast sensitivity can have serious problems seeing distinct images under certain conditions.Even if you have 20/20 vision, you could have poor contrast sensitivity. Contrast sensitivity testing is important because it allows eye doctors to determine how well you function in real-world conditions where objects may "blend" and become indistinguishable in backgrounds with similar coloring.


What Are Symptoms of Low Contrast Sensitivity?

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 is crispness of vision, enabling us to see objects that do not stand out from their backgrounds. Contrast sensitivity is often referred to as "functional vision" beyond how well you see details on a standard eye chart.If you have low contrast sensitivity, you may have problems with night driving, including inability to see traffic lights or spot other cars and pedestrians. People with poor contrast sensitivity also may require extra light to read, and their eyes may become tired when they read or watch television. Poor contrast sensitivity also can cause you to stumble when you fail to see that you need to step down from a curb onto similarly colored pavement.Low contrast sensitivity also can be a symptom of certain eye conditions or diseases such as cataracts, glaucoma, or diabetic retinopathy. Also, reduced contrast sensitivity sometimes can occur as a usually temporary side effect of laser vision surgery procedures including LASIK and PRK. Lack of contrast sensitivity is not the same as blurred vision, however.


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.

A person's ability to see objects against low contrasting backgrounds is expressed as a contrast sensitivity function (CSF). Your eyes will be measured to determine the lowest contrast at which certain objects such as bars or dots can be seen, relative to their backgrounds.Some eye doctors administer the contrast sensitivity test as part of a routine screening. If your eye doctor determines that you need a contrast sensitivity test, it likely will be administered after the visual acuity test that determines your ability to see details such as letters or numbers on an a standard eye chart.Contrast sensitivity testing likely will be done while you wear your eyeglasses or contact lenses, if you require vision correction. Unlike standard visual acuity testing, both eyes are tested together to determine ability to see low-contrast objects. You will be asked to look at a low-contrast test chart, with images such as bars or dots shown during a sequence of increasingly lower contrasts until you can no longer identify them.For evaluation of eye disease, contrast sensitivity is tested on each eye individually. Contrast sensitivity is also used to assess visual performance, such as for athletes or contact lens wearers, or after refractive surgery such as LASIK. In this case, unlike conventional acuity testing, both eyes may be tested together to assess how you see in the real world with both eyes working together.

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