Assessment of cyclodisparity-induced slant perception with a synoptophore

Abstract

Purpose

To evaluate with a synoptophore slant perception induced by binocular cyclodisparities in normal subjects and to argue for the possibility of abnormal slant perception in patients with cyclo-vertical strabismus.

Methods

A vertical line with cyclodisparities that ranged from 0° to ± 10° was presented to 17 normal subjects (mean ± SD age, 28.4 ± 5.6 years; 11 men and 6 women) with a synoptophore, and the perceived slant of the line in the pitch plane was measured by a matching method. Cyclodisparity thresholds for top-away and top-forward slants were also evaluated by the method of limits in a separate experiment.

Results

An incyclodisparity induced top-forward, while an excyclodisparity induced top-away, slant perception. The maximum slant angle was 37° on average at a cyclodisparity of 10°, and the mean slant gain (perceived angle/geometrically calculated angle) was 64 ± 13%. The mean cyclodisparity thresholds for top-away and top-forward slants were −1.1° and 0.6°, respectively.

Conclusion

The slant perception induced by cyclodisparities was reasonably assessed with the synoptophore. The cyclodisparity thresholds obtained in this experiment were much lower than the cyclodeviation range of the patients, indicating that a considerable number of patients may have abnormal slant perception once they achieve sensory fusion.