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To the Editor:
We read the editorial on visual rehabilitation by Drs. Glisson and Galetta who comment on vision restoration therapy (VRT).1 As mentioned by the authors, the majority of treated patients experience subjective functional improvement. The precise mechanism of action of the therapy is less important than the therapy that works in the majority of patients. One issue involves the process responsible for the visual field changes noted after VRT. As in many biological processes, there may be several mechanisms responsible for particular observations.
We believe that one of the mechanisms of action likely relates to cortical reorganization. The literature on neuroplasticity is growing and cortical reorganization after analogous rehabilitation for other sensorimotor interventions is documented in other cortical areas. In patients with visual field defects, visual stimulation paradigms have resulted in cerebral changes noted on PET2 and a recent report showed fMRI changes associated with VRT.3
The authors state the improvement noted on a suprathreshold perimetric strategy was not reliably reproduced with other perimetric techniques. While this observation may appear to be true based on the data cited, their statements only reflect a partial view of the available literature. Many studies other than those noted in their editorial have shown visual field improvement on near threshold perimetries, including most recently an eye tracker study.4
This study addresses their concerns about saccadic eye movements into the blind field, demonstrating that patients maintained their eyes within 2° of fixation 98.9% of the time (in the horizontal axis). In addition, saccades occurred as frequently towards the seeing field as to the blind field, and large saccades >5° in the direction of the blind field were very rare.
Disclosure: Dr. Firlik is Chairman of the Board of …
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