FAQs

What is "contrast" and "contrast sensitivity"?
Contrast is the difference in brightness that separates an object from its background. Contrast sensitivity is a person's ability to identify an object from its background.

How is contrast sensitivity tested?
Contrast sensitivity is tested by viewing targets of varying contrast and size (spatial frequency) to relate to how well a person functions visually to see everyday objects.

What is the difference between information collected by contrast sensitivity and the Snellen test?
The Snellen test measures one's ability to see small, well-defined black letters on a white background, which is a high contrast test. Most objects we see are larger and have a lower contrast, such as faces or road signs. Contrast sensitivity testing uses sine-wave gratings of different frequencies and contrast levels. It more accurately reflects how well patients see everyday objects and perform visual tasks under a variety of image sizes and contrast conditions. The Snellen acuity measures quantity - contrast sensitivity measures both quantity and quality.

Can someone have both good vision under high contrast conditions yet poor visual performance under low contrast conditions?
Yes. Many people can read the 20/20 line on the Snellen chart yet still complain about visual difficulties under low contrast conditions, such as driving at night. Such poor visual performance may be caused by normal variation, age, ocular disorders or ocular pathology.

But isn't 20/20 visual acuity the standard for good vision?
Because visual acuity measures how well a person can identify black on white letters, seeing the 20/20 line only relates to a one size high contrast object. Contrast sensitivity uses gratings to measure visual performance over the full range of sizes and contrasts needed to perform everyday visual tasks such as identifying people and reading signs.

How is contrast sensitivity tested?
Contrast sensitivity is tested with special contrast test charts, such as the Ginsburg FACT chart, that can be used like visual acuity charts inside view-in testers or on a wall.

How does this test work?
Contrast sensitivity testing using the sine-wave gratings is very similar to methods used to test hearing. The grating size can be compared to sound frequency in hearing. The contrast is similar to loudness in hearing. The visual threshold to see the gratings provides a curve, as shown in the introduction on the first page, similar to the loudness threshold curve (audiogram) in hearing.

What does a contrast sensitivity curve tell your doctor about your vision?
The shape of the curve indicates how well your visual system is performing. If your curve is lower than the established normal range, or changes over time, it can alert the doctor to further evaluate or closely monitor your vision. Contrast sensitivity testing helps doctors provide better patient care.

What could cause a loss of contrast sensitivity?
A loss may be due to corrective lens or contact lens problems, ocular pathology, medications, systemic health problems or simply individual variations. The contrast sensitivity curve can assist your doctor in determining the status of your ocular health or problem.

Can contrast sensitivity change with age?
Yes. Research has shown that infants and older patients often have lower contrast sensitivity than young adults. With the added information of contrast sensitivity data, doctors can then determine what is normal for their patients.

What if I have no known ocular or medical problems and yet my curve is low?
Contrast sensitivity testing may help your doctor with an earlier diagnosis of ocular disease. This is particularly true for patients whose contrast sensitivity curve is low in the portion of the visual system not tested by acuity.

How often should contrast sensitivity be tested?
Because it is a more comprehensive and accurate way to assess visual health and measure visual performance, contrast sensitivity should be tested routinely so that any changes or losses in vision can be effectively monitored. Testing can be done before and after treatment or procedures to determine effectiveness.

There are several types of contrast sensitivity tests available. What are the differences between these tests?
There are two general types of contrast sensitivity tests: sine-wave grating tests and low contrast letter tests. A method to analyze the different contrast tests and why the grating test is a more sensitive and comprehensive vision contrast test than the low contrast letters for a large number of scientific and clinical reasons can be found in: Ginsburg AP, Next Generation Contrast Sensitivity Testing, In Rosenthal B, Cole R (ed): Functional Assessment of Low Vision, St. Louis, 1996, Mosby-Year Book, Inc., pp 77-88.

The bottom line is that sine-wave contrast sensitivity testing is unparalleled in providing optimum sensitivity and comprehensiveness for testing vision contrast.

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