Vision Therapy in Adults with Convergence Insufficiency: Clinical and Functional Magnetic Resonance Imaging Measures

Abstract

Purpose This research quantified clinical measurements and functional neural changes associated with vision therapy in subjects with convergence insufficiency (CI). Methods 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. Results Convergence average peak velocities to step stimuli were significantly slower (p = 0.016) in CI subjects compared with controls; however, significant differences in average peak velocities were not observed for divergence step responses (p = 0.30). The investigation of CI subjects participating in vision therapy showed that the nearpoint of convergence, recovery point of convergence, and near dissociated phoria significantly decreased. Furthermore, the positive fusional vergence, average peak velocity from 4° convergence steps, and the amount of functional activity within the frontal areas, cerebellum, and brain stem significantly increased. Several clinical and cortical parameters were significantly correlated. Conclusions Convergence peak velocity was significantly slower in CI subjects compared with controls, which may result in asthenopic complaints reported by the CI subjects. Vision therapy was associated with and may have evoked clinical and cortical activity changes.

Effect of oculomotor rehabilitation on vergence responsivity in mild traumatic brain injury

“…A combination of repeated stimulation with various amounts and types of disparity (crossed and uncrossed), increasing task-level difficulty, active participation of the subjects, increased attention, presence of visual and verbal feedback, and high motivation of the subjects to perform the task over the 6 wk training period resulted in a significant OMT effect. These ideas are further supported by a recent study [42] that evaluated the neurological changes using the functional magnetic resonance imaging technique in two individuals with mTBI before and after intensive vergence-based OMT. Their results showed increased amount of voxels and correlation within specific regions of interest (brain stem, cerebellum, frontal eye fields, and supplementary eye fields) following a total of 18 h of clinically based and laboratory-based vergence OR, similar in nature to that conducted in the present study.…”

“…Vergence dynamics were markedly slowed (i.e., reduced peak velocity) for convergence but not for divergence, as has been found earlier in larger populations [42].…”

“…Based on the results of the present study at baseline, and earlier studies [41][42], the primary neural deficit in the patient with mTBI is believed to be the pulse. This is reflected in the consistently slowed dynamics (e.g., reduced peak velocity and increased time constant) for both convergence and divergence in the present study prior to OMT, which can be accounted for by a reduction in pulse height.…”

“…Lastly, in a recent pilot study, objective recordings of vergence were obtained in two young adults with selfreported mTBI and nearwork symptoms [42]. Vergence dynamics were markedly slowed (i.e., reduced peak velocity) for convergence but not for divergence, as has been found earlier in larger populations [42].…”

“…The compromised white matter integrity causes slowed conduction of nerve impulses [85][86], thus resulting in an overall slowed response (e.g., slowed vergence). In addition, the decreased number of synapses, reduced firing rate, reduced neural synchrony, and lack of correlation within and across the specific brain regions cause loss of automaticity and an overall reduction in the system's maximum amplitude (e.g., NPC) [42]. Figure 5 shows the schematic representation of the proposed neurological mechanisms involved based on the aforementioned laboratory findings.…”