Stereoacuity degradation by experimental and real monocular and binocular amblyopia

Fourteen normal adult volunteers with normal binocular single vision and normal stereoacuity submitted to monocular and binocular degradation of their stereoacuity by cycloplegia and fogging with spherical lenses. Stereoacuity (SA) was reduced as soon as visual acuity (VA), both monocular and binocular, was reduced. There was a marked similarity in the degree of SA reduction produced by monocular and binocular amblyopia. The degree of SA reduction was slightly more marked with monocular decrements than with binocular at VAs between 20/25 and 20/50. Significant intersubject variation was noted. The majority of subjects maintained gross SA at 20/200 monocular or binocular. One subject was reduced to gross stereopsis at 20/30 monocular and 20/50 binocular VAs. Two subjects were able to retain 40 sec of SA until vision was degraded to 20/50. Conversely, 40 sec of SA was not achieved by any subject at monocular or binocular vision less than 20/40 (test for malingering). Thirteen patients with real monocular and binocular organic or functional amblyopia were then compared with the experimental group. On the whole, patients scored somewhat better than normals but their scores fell within the range of responses found in the normal group.