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Matteo Tomasi, Alexandra R Bowers, Eli Peli, Gang Luo; Compensatory gaze scanning by patients with hemianopia during outdoor walking. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4131.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether patients with hemianopia demonstrate compensatory gaze scanning to their blind side when walking outdoors, with and without visual field expansion prisms.
9 patients with homonymous hemianopia walked 0.8-mile routes on busy downtown streets on two occasions, 1.5 months apart. At each visit they walked one route with and one without 57Δ peripheral prism glasses. Eye movements were tracked using a head-mounted camera system. Head position relative to body was measured using a pair of motion sensors (one on the head and one on the trunk). Head and eye positions were synchronized and combined to generate gaze position relative to body (approximately the walking direction). Gaze fixations and eye fixations were detected using a speed criterion of <15°/s. The percentage of gaze and eye fixations exceeding specific visual directions (e.g., >20°, >30°, >40°) relative to primary body and eye position, respectively, were analyzed using repeated-measures ANOVAs to evaluate the effects of side (seeing/blind) and prism (with/without).
For gaze fixations, patients looked far peripherally (30°) from their body heading direction toward the blind side significantly more often than toward the seeing side (7.2% of total valid samples vs. 5.7%, p = 0.049; data pooled for with and without prisms). However, the number of gaze fixations to the far periphery was lower with vs. without the prisms on both the blind and seeing sides, but to a greater extent on the seeing side (blind side 6.7% vs 7.7%; seeing side 4.7% vs 6.7%, p = 0.018). No significant effects of side or prism were found for the eye fixation data.
These preliminary results suggest that hemianopes make larger compensatory gaze scanning movements towards the far periphery on their blind than their seeing side. They make fewer scans to the far peripheral region with the prism glasses than without; but that effect is found also on the seeing side and in fact the effect on seeing side is larger. These data suggest both a beneficial effect of the prism expansion on the blind side, as well as, a possible shift of attention from the seeing to the blind side when using the prism glasses. The lack of significant effects in the eye movement data indirectly suggests the important role of head movements in compensatory scanning in natural walking conditions.
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