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Dennis Ireland, Barclay Bakkum, Robert Donati; Oculomotor endurance therapy for convergence insufficiency increases duration of near task performance. Journal of Vision 2009;9(8):276. doi: 10.1167/9.8.276.
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In a majority of patients with convergence insufficiency, the ability to attain appropriate fusion ranges has been successfully restored by vision therapy. Clinically, though, a portion of these patients complain that they still cannot perform near vision tasks for an adequate/acceptable amount of time without suffering eye strain/fatigue.
Standard vision therapy protocols used to treat convergence insufficiency include training tasks that increase extraocular muscle strength and neuromuscular coordination. Interestingly, they do not, however, suggest tasks with the purpose of decreasing the fatigability of the extraocular muscles, and therefore, increasing endurance in these muscles. The purpose of this n-of-1 study was to determine if adding endurance-type training to a standard vision therapy protocol used by a subject with convergence insufficiency could lengthen the time that a near vision task (reading) could be performed before eye strain occurred. The subject of this study had already successfully undergone standard vision therapy for a convergence insufficiency, such that appropriate fusion ranges could be obtained. Unfortunately, the subject could still perform a near vision task (read) for only about 10 minutes before eye strain occurred. In this study, endurance-type training was incorporated into a standard vision therapy protocol by progressively lengthening the amount of time that an appropriate fusion range was held during exercise sessions over twelve weeks. After twelve weeks, the subject could hold an appropriate fusion range in the vision therapy exercises for 35 seconds with no discomfort. Also, the subject could perform a reading task for 60 minutes with no eye strain/fatigue. The results of this study support the idea that endurance-type training could be added to standard vision therapy protocols for patients with convergence insufficiency that, even after gaining the ability to attain appropriate fusion ranges, still cannot perform near visions tasks for an adequate/acceptable amount of time.
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