Role of the vertical muscles in horizontal deviations.

This study was prompted by the observation that after horizontal muscle surgery a large number of cases of non-paralytic squint ended up with no binocular vision and an appreciable residual vertical deviation with a "V" or "A" pattern. It has become clear to us that the associated vertical deviation is usually present from the onset, and may play a major part in the mechanism of the squint. In less marked cases the vertical deviation is noticed only when the eye movements are fully examined, and is missed unless the extremes of elevation and depression are evoked. We have been largely influenced by the work and experience of Dr. M.H. Gobin (1964, 1968a, b, c), who feels that cyclotropia is an important factor in the aetiology of convergent squint. Gobin regards torsion as a third dimension in ocular motility, and thinks that for images to fall on corresponding retinal points it is reasonable to try to make the visual axes parallel horizontally and vertically, and that the retinal meridians should coincide.