Measuring depth perception in stereoamblyopia by using a suprathreshold stimulus

Abstract

Stereotests based on random distribution pattern (global stereopsis) show disadvantages when giving larger disparation, because subjects with limited fusion-ability do not recognize them, while realistic shapes of objects (contour stereopsis) are usually fused. Because of this random dot tests can not always be utilized to verify subnormal stereo-ability. This paper describes a way of testing stereo-ability not by approaching stereo-angle-thresholds but by presenting supra-threshold stimuli and evaluating the emphasized subjective "elevation level" readings. With this method I examined normosensoric healthy subjects and compared them to subjects with different binocular defects. The subjective sensations correlate well with the clinical impression of what those patients, known at the department for long periods, should be able to differentiate. There is no evidence that healthy people are fully competent while "cured" strabismus cases should be incompetent. Indeed a gradual decrease of stereo-ability is seen. We strive for a really simple finger test in terms of subjective depth perception as a quick halfprecise office check.