Eye care specialists and clinical vision scientists most often evaluate contrast sensitivity with low contrast visual patterns (e.g. letters, numbers and other symbols) and determine how little contrast you can tolerate while still identifying the pattern correctly.
With our product, the Mars Contrast Sensitivity Test (letter version shown below), a person reads letters (or numbers) from left to right and from top to bottom on the chart. The final letters (or numbers) correctly identified determine a log contrast sensitivity score, which ranges from 0.04 to 1.92. (For full details on how log contrast sensitivity scores are derived, see here).
For example, with the Mars test shown here, a person reads letters from left to right and from top to bottom on the chart. The final letters correctly identified determine a log contrast sensitivity score, which ranges from 0.04 to 1.92. If the person can read only the blackest letters, their score will be close to zero, whereas if they can read the very faintest letters on the chart their score will be closer to 1.92 (For details on why these specific numbers are used see Technical Details of Mars Contrast Sensitivity Tests.)
Note that this is quite different from the standard Snellen letter chart displayed in many doctors’ offices and other settings such as the Department of Motor Vehicles, which shows letters of decreasing size. With the traditional test, the minimum size at which you can correctly identify letters determines your visual acuity. But with the Mars, it is the minimum contrast that determines your threshold and your contrast sensitivity.
