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R.G. Giorgi, R.L. Woods, R.B. Goldstein, E. Peli, T. Bond, R.D. Easton; Extended Wearing Trial of Peripheral Prism Visual Aid for Homonymous Hemianopia . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1399.
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Purpose: Homonymous hemianopia (the loss of vision on the same side in each eye) impairs patient ability to navigate and walk safely. We evaluated a novel, prism field expansion correction for hemianopia in an extended wearing trial (Peli, 2000, Optom Vision Sci, 77: 453). The impact of the prisms on subjects’ functional performance on several measures was evaluated. Methods: 11 subjects with homonymous hemianopia (4 left; 7 right) with neither visual neglect nor cognitive decline participated in the 7–visit study. To extend the horizontal visual field, subjects’ spectacles were fitted with both upper and lower Fresnel prism segments (40 PD) across the lens on the side of the visual field loss only. Subjects were asked to wear these peripheral prism glasses as much as comfortably possible for the duration of the study, which averaged 9 (range: 5 to 12) weeks. Adaptation to the change in perceived direction through the prisms was evaluated using a pointing task at 4 of 7 visits. Way–finding (walk safely to directed locations) and cognitive mapping in an unfamiliar environment (large shopping mall) and perceived quality of life (questionnaires) were evaluated at the start and end of the study. Results: Visual Field: About 20º field expansion in upper and lower quadrants was demonstrated for all subjects (binocular perimetry, Goldmann V4e). Perceived Direction: Only 2 subjects demonstrated a transient, and conscious adaptation to the change in visual direction produced by the prism. Clinical Success: Subjects reported wearing the glasses for an average of 4.1±4.0 hours/day. At the end of study 6 of 11 subjects reported benefit and that they would continue wearing the device. 1 to 3 months after study end, 5 of these 6 subjects reported still habitually wearing the aid. Mall: Way–finding and cognitive mapping had improved at the end of the study, but this appears to have been a practice effect. Quality of Life: At study end, reduced difficulty with noticing obstacles to the side (p=0.07) and moving in stores (p=0.12), but increased difficulty with curbs (p=0.06) was reported. Conclusions: Peripheral prism glasses provided reported benefit (usually in obstacle avoidance) to about half the subjects in the study. The limited improvement in measured functional performance may have been due to insensitive measurement techniques, a study wearing period that was too short, or suggest that additional training is required.
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