[Vertical and tortional deviations in early strabismus].

Abstract

The occlusion of one eye may trigger two types of deviation: 1) Heterophorias: the occluded eye deviates towards a horizontal, vertical or torsional abnormal position of rest. Fusion keeps the eyes straight during binocular fixation. 2) Dissociated deviations, horizontal (DHD), vertical (DVD), torsional (DTD): they are found in infantile strabismus. The deviation without fixation is always smaller than the deviation of the occluded eye. The more typical cases are the ones where the position of rest without fixation is an orthoposition. Normal binocular vision is lacking. Most of the time, an alternant neutralisation is found: the occlusion deviation is not the return of the occluded eye to an abnormal position of rest. The deviation is caused by a disequilibrium of binocular retinal stimulations. Horizontal and vertical deviations are easy to study. It is not the case in dissociated torsional deviation (DTD) where the incyclotorsion does not exist when fixation is absent. An indirect proof of extorsion is given by the study of horizontal and vertical deviations determined in the cardinal position of gaze. Extorsion of the globus leeds always to abnormal actions of the recti. This give a typical synoptometer chart which is found in any extorsion whatever its origins: paralysis, alphabetic patterns or infantile strabismus. Dissociated extorsions are always associated with a bilateral elevation in the primary position. Dissociated deviations are found in infantile strabismus with the other dissociations phenomenon such as nystagmus, optokinetic nystagmus asymmetry, fixation in adduction preference (and incyclotorsion).