Spasm of the near reflex triggered by disruption of normal binocular vision.

A 26-year-old healthy female was referred by her optometrist to the binocular vision clinic of our institution for the investigation of an accommodative spasm occurring during monocular conditions. Corrected binocular visual acuity was 20/20 (6/6), with normal pupils and good ocular alignment. When the fellow eye was covered, visual acuity was <20/200 (6/60) in each eye, miosis was present in both eyes, and the occluded eye was in esodeviation, indicating a spasm of the near reflex. The spasm disappeared when a translucent occluder was used instead of an opaque black occluder. Further investigation permitted us to establish that dioptric and nondioptric blur, as well as reduced light transmission, also triggered the spasm of the near reflex, but only for specific power, opacity, or density. Cycloplegia did not eliminate the spasm. Comparisons are made with the single other similar case found in the literature. Assumptions are made as to the possible causes of that intermittent spasm.