I L Bailey¹, S N Fitz¹, G A Akinlabi¹, K Lin²
¹University of California, School of Optometry, Berkeley, United States; ²Southern California School of Optometry, Optometry, Fullerton, United States
Computer-based tests have been developed for the clinical assessment of contrast sensitivity on the efficiency of search and on the detection of dynamic targets. For the search task, a series of 6 display screens each presents randomly-positioned numbers that are ordered in contrast. The subject's task is to quickly touch the numbers in sequence. Another test presents an object, usually a large solid square, in one of four randomly assigned quadrants on the screen. The object may be blinking, moving or static. The subject's task is to identify or touch the quadrant containing the target. We use 6 series of presentations, and within each contrast is reduced in 0.3 log unit steps. Speed and accuracy of performance a can easily be monitored using a touch screen or responses from the subject or the clinician using a mouse or keyboard. With both kinds of tests, we obtain a measure of contrast threshold and a profile of the speed of response as a function of contrast. We find systematic changes in the threshold and speed as a function of target size for sizes smaller than 3 degrees. In low vision subjects, we find considerable diversity in speeds and in the relationships between speeds and contrast. In general, the search task gives the same contrast thresholds as those obtained in standard clinical tests. Having a dynamic element such as flicker or motion in the target significantly improves contrast sensitivity for detection. These tests might prove to better indicators of functional abilities.
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