The Effects of Central and Peripheral Binocular Visual Field Masking on Fusional-Disparity Vergence

Zoran Georgievski, BAppSc (Orth)Hons

Clinicians have long recognised the effectiveness of the peripheral fusion mechanism in eliciting fusional movements and have employed this in the investigation and treatment of squint. In 1939, Burian was the first to demonstrate that fusible stimuli placed in the peripheral binocular field only, were capable of producing fusional movements. The aim of the present study was to investigate the effects of masking of the central and peripheral binocular fields to determine the influence of each on the horizontal fusional amplitudes, and on the duration of jump fusional-disparity convergence movements in normal binocular vision. Twenty one (n=21) young adult subjects took part in the study. The fusional amplitudes were measured with a Risley rotating prism. The jump vergence movements were assessed using an infra-red eye movement recording system. Measurements were performed at 3 meters using full, central and peripheral field stimulus conditions. It was found that under central stimulation, the fusional amplitudes for both base-in (p=0.0008) and base-out (p<0.0001) directions were significantly lower than those under peripheral stimulation. Also, peripheral field masking significantly prolonged the duration of a disparity vergence response induced by a 10Δ base-out ‘prism (p=0.0009), but not by one of 5Δ (p=0.0507). It was concluded that peripheral fusion plays an important role in the production of fusional-disparity vergence eye movements.