This research quantified clinical measurements and functional neural changes associated with vision therapy in subjects with convergence insufficiency (CI).
Convergence and divergence 4° step responses were compared between 13 control adult subjects with normal binocular vision and four CI adult subjects. All CI subjects participated in 18 h of vision therapy. Clinical parameters quantified throughout the therapy included: nearpoint of convergence, recovery point of convergence, positive fusional vergence at near, near dissociated phoria, and eye movements that were quantified using peak velocity. Neural correlates of the CI subjects were quantified with functional magnetic resonance imaging scans comparing random vs. predictable vergence movements using a block design before and after vision therapy. Images were quantified by measuring the spatial extent of activation and the average correlation within five regions of interests (ROI). The ROIs were the dorsolateral prefrontal cortex, a portion of the frontal lobe, part of the parietal lobe, the cerebellum, and the brain stem. All measurements were repeated 4 months to 1 year post-therapy in three of the CI subjects.
Wearing aspheric lenses with negative SA shifts the mean SA of the unaccommodated eyes from +0.05 μm (eyes only) to −0.029 μm (eyes + SVCL) and increases the negative SA for the eye + lens when accommodating from −0.029 to −0.07 μm for natural pupils. Aberration changes with accommodation were attenuated by the accommodative pupil miosis, which reduced binocular viewing pupil diameters from 3.9 to 3.3 mm. This alteration of the typical SA levels by the aspheric SVCL did not prevent accurate accommodation (mean ± standard deviation accommodative lag under binocular viewing were −0.08 ± 0.12D, −0.38 ± 0.12D, and −0.26 ± 0.08D for paraxial, minRMS, and peak IQ, respectively).
These data clearly show that aspheric contact lenses designed to correct some or all of the unaccommodated eye’s positive SA do not interfere with accommodation.