Abstract
For midline targets vergence and accommodation between the two eyes are believed to be symmetrical, controlled by unitary commands and both facilitated by cross-links. These are important considerations in strabismus treatment. We have previously demonstrated that for midline smooth pursuit, under monocular viewing, the covered eye does not follow the viewing eye while accommodation remains symmetrical, questioning the unitary vergence command and cross links. The purpose of this study was to see if the saccadic or jump vergence system, shared similar characteristics. Subjects underwent a detailed clinical examination to confirm typical visual and oculomotor characteristics. Subjects were seated at the end of a 6-meter track with their head resting securely on a chin rest. Subjects alternated on command between fixation on a far target (350 cm) to a near target (33 cm) as it flashed in front of them along the midline. Eye movements and accommodation were simultaneously measured with the PlusOptix PowerRefractor. Data was collected from both eyes during binocular viewing and during monocular viewing with the fellow eye occluded with an IR passable filter. During binocular viewing saccadic/jump vergence was synchronous between the two eyes as was accommodation. However, during monocular viewing, the occluded eyes for all subjects showed variable eye movements from desynchronized jump vergence to conjugate saccadic movement while accommodation remained symmetrical between eyes. Comparisons of the linear regression slope of each eye for vergence and accommodation and standard calculation of vergence confirmed these results to be true. Our results suggest that during monocular midline saccadic/jump vergence the covered eye is not under a unitary vergence command and indicates the absence of the putative cross-link where accommodation drives vergence. This is similar to our previous results with monocular pursuit vergence user a similar paradigm suggesting these characteristics are not reserved for one set of eye movements.