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A.R. Bowers, K. Keeney, D. Apfelbaum, E. Peli; Multi–Site Extended Wear Trial of Peripheral Prisms Visual Field Expansion Device for Patients With Hemianopia . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3489.
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© ARVO (1962-2015); The Authors (2016-present)
Peripheral prism glasses, a novel visual field expansion correction for hemianopia (Peli, 2000, Optom Vis Sci, 77: 453), showed promise in a small sample study (Giorgi et al, ARVO 2004). We evaluated fitting procedures, patient acceptance, and functional utility of the glasses over a longer time period, in a larger scale, community based, multi–site extended wearing trial.
Fifty patients with homonymous hemianopia (25 right, 25 left; age 62 ± 14 yrs) with neither visual neglect nor significant cognitive decline were enrolled at 16 vision rehabilitation clinics. The Schepens Eye Research Institute acted as the coordinating and data management center. Low vision practitioners fitted patients’ spectacles with upper and lower press–on Fresnel prism segments (40 PD base–out) across the lens on the side of the visual field loss following protocols set up by the coordinating center. Patients were encouraged to wear the prism glasses as much as possible. Practitioners conducted follow up interviews and questionnaires at 2 weeks (telephone) and 4 weeks (in–office), when a clinical decision whether to continue wear was made. Patients who continued wear were interviewed again (telephone) after 6 to 12 months (average 10 ± 3); a permanent PMMA Fresnel prism embedded in the carrier lens was developed and provided to 13 of these patients.
Of the 50 patients enrolled, 38 completed all visits and 12 withdrew (6 before and 6 after prisms were fitted). At 4 weeks, 32 patients continued wear and 6 discontinued. Median wearing time was 5.5 hours/day (interquartile range 2.3 to 14.3) and median inter–prism separation was 11.0 mm (interquartile range 8.5 to 11.5). Those who continued were younger than those who discontinued (62 ± 21yrs and 74 ± 14yrs, respectively; p = 0.07), reported more comfortable vision with the prisms (p = 0.02) and gave higher ratings of prism helpfulness in obstacle avoidance when walking (p < 0.001). At the long term follow up interview, 19 reported still wearing the prisms, 8 no longer wore the prisms, 1 was deceased and 4 have yet to be contacted.
Peripheral prism glasses were successfully fitted by community low–vision practitioners, and provided reported benefits in mobility and obstacle avoidance for the majority of patients in this study. Clinical success rates are encouraging: of all subjects fitted with prisms (n = 44), 73% (32/44) chose to continue wear at 4 weeks and at least 43% (19/44) were still using the prisms in the longer term (> 6 months).
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