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Jenny Shen, Eli Peli, Alex R. Bowers; Effect of Motion on Detection with Unilateral Peripheral Prisms for Hemianopia. Invest. Ophthalmol. Vis. Sci. 2011;52(14):390.
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Unilateral peripheral prisms (EP prisms) are used to expand the visual field in patients with homonymous hemianopia (HH), shifting images from the non-seeing field to the seeing field in one eye (Peli 2000). In binocular viewing, an area of peripheral rivalry results that could lead to double vision or suppression. Previously we found little evidence of binocular suppression of the prism image on static noise image backgrounds. Using natural image and motion video backgrounds, this study assesses detection with the EP prisms in conditions that more closely approximate the real world.
2 subjects with HH and 2 normal vision subjects with simulated HH were tested wearing unilateral 40Δ Fresnel press-on EP prisms. A computerized perimeter was used to measure detection rates on driving video backgrounds and still frame images (extracted from the videos) in binocular and monocular (prism eye) viewing. To avoid floor and ceiling effects, target size and contrast were individually determined for each type of background. Targets were presented in the prism expansion area (PEXP) and the seeing hemifield area (SHF). Binocular suppression was evaluated by conducting within-subjects comparisons of detection rates under monocular and binocular viewing for each area on the still frame and moving video backgrounds. Effects were similar in the HH group and the simulated HH group; therefore data were collapsed across the groups.
On the video backgrounds, PEXP detection rates were significantly reduced in binocular viewing compared with monocular viewing (medians 19% IQR 11%, and 78% IQR 14%, respectively, p = 0.03). However, on the still frame backgrounds, there were no differences in PEXP detection rates for binocular and monocular viewing (89% IQR 17%, and 89% IQR 9%, respectively, p = 0.23). Detection in the non-prism SHF was also similar in binocular and monocular viewing for both still frame (96% IQR 8% and 94% IQR 4%, p = 0.21) and video backgrounds (96% IQR 3% and 96% IQR 4% p = 0.09).
Preliminary results indicate partial suppression of the prism image under binocular viewing on a video background. However, consistent with our previous findings, binocular suppression did not occur on the still frames. Thus image motion seems to be a key factor. Further testing is needed to quantify the extent to which binocular suppression might affect the utility of EP prisms in dynamic real-world situations.
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