Clinical testing of contrast thresholds using a commercial television monitor system.
Algis J Vingrys, Andrew J Anderson
Clin Exp Optom | Published : 1998
Background: The Medmont AT-20 has incorporated a contrast threshold test using a predetermined letter size that can be applied in clinical settings. This paper describes a pilot study that evaluates this technology and the effects of certain parameters on test outcomes. Methods: A photometric calibration of the test was performed to define the relationship between the AT-20 scale and Weber contrast (W%). We determined the effects of repeated measures (precision), target size (6/6 to 6/96), viewing duration (50 to 1,000 msec), defocus (+0.50 to +1.50 DS) and a macula scotoma on thresholds. The accuracy of the staircase (PEST) procedure was evaluated with and without false-negative responses. ..View full abstract