Spatial aberrations and acuity in strabismus and amblyopia.

Spatial uncertainty and distortion were quantified from judgement of the horizontal position of a flashed 0.5 deg vertical line with respect to a flanking reference target in strabismics with and without reduced acuity. Spatial uncertainty was outside the range of 30 normal eyes in all of 23 strabismic amblyopic eyes (visual acuity = 20/40 or worse) and in 20 of 22 squinting eyes with 20/30 or better acuity. Abnormal spatial distortion was found in 16 amblyopic and 10 squinting eyes. In the deviated eyes of the strabismics, the extent of spatial uncertainty and distortion correlated with visual acuity. Spatial aberrations were not accounted for by strabismics' unsteady or eccentric fixation, nor were they mimicked in normal eyes when visual acuity was artifically reduced. The authors suggest that spatial uncertainty and distortion represent the primary abnormalities in strabismics and produce deficits of visual acuity according to their severity.