title: Binocular deficits associated with early alternating monocular defocus. I. Behavioral observations.
abstract: To study the binocular vision deficits associated with anisometropia, monkeys were reared with alternating monocular defocus, which allowed monocular mechanisms to develop normally while binocular mechanisms were selectively compromised. A defocusing contact lens of -1.5 D, -3 D, or -6 D was worn on alternate eyes on successive days (n = 3 per lens power) from 3 wk to 9 mo of age. The control subjects were two normally reared monkeys and two human observers. Functional binocular vision was assessed through behavioral measurements of stereoscopic depth discrimination thresholds as a function of spatial frequency. To characterize the extent of the deficits in disparity processing at a given spatial frequency, the contrast required to support stereopsis was determined for a range of disparities that exceeded the subjects' measured stereoacuity. The lens-reared monkeys showed spatial-frequency-selective deficits in stereopsis that depended on the magnitude of the simulated anisometropia experienced during the rearing period. For a given spatial frequency, the treated monkeys generally required higher than normal contrasts to support stereopsis even for large disparities. Moreover, a given increase in contrast produced smaller than normal improvements in stereo discrimination in our treated subjects, which suggests that in addition to deficits in contrast sensitivity, disparity-sensitive mechanisms exhibited low contrast gains. The spatial-frequency selective nature of the binocular deficits produced by the imposed anisometropia indicate that disparity processing mechanisms are normally spatial-frequency selective and that mechanisms tuned to different spatial frequencies can be differentially affected by abnormal binocular visual experience.
authors: University of Houston, College of Optometry, Houston, Texas 77204-2020, USA. Jwensveen@uh.edu
authors: Janice M
authors: JM
authors: Wensveen
authors: Ronald S
authors: RS
authors: Harwerth
authors: Earl L
authors: EL
authors: Smith
mesh_terms: D000550:Amblyopia / Q000503:physiopathology*; D000818:Animals; D008253:Macaca mulatta; D010775:Photic Stimulation / Q000379:methods; D014786:Vision Disorders / Q000503:physiopathology; D015357:Vision Disparity / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology*; D015349:Vision, Monocular / Q000502:physiology*