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Matteo Tomasi, Jeffrey Churchill, Jean Paul Wiegand, Kevin Houston, Eli Peli, Alexandra Bowers, Gang Luo; Peripheral Prisms Increase Blindside Eye And Head Scanning Movements During Outdoor Walking In Hemianopes: Preliminary Results. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2758.
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Peripheral prism glasses are used as a field expansion device for hemianopia. As the field expansion is always present at all lateral gaze positions (unlike other designs), it should provide a constant stimulus to initiate eye and/or head movements to the blind side. We tested the hypothesis that peripheral prisms would increase eye and head scanning movements toward the blind hemifield in an outdoor walking task (as gaze behaviors in lab-based tasks may not be representative of those in a natural environment).
To date 7 people with homonymous hemianopia walked 0.8-mile routes on busy downtown streets, with and without prism glasses, on two occasions: immediately after receiving peripheral prism glasses and 1.5 months later. Between the two visits, each subject received 12 hours of in-lab perceptual-motor training with the prism glasses and wore the device at home on a daily basis. During the walks, their eye and head movements were recorded using a head mounted eye tracker and inertial motion sensors, respectively. We defined the neutral point as the most frequent sample of the distribution for eye movements, and the standard anatomical position for head movements. We analyzed the eye/head movements within the blind and seeing sides (with respect to the neutral point) as the sum of the amplitudes divided by the total number of samples. A 10° range around the neutral point was excluded to minimize the impact of random and less-meaningful fluctuations. A repeated-measures ANOVA was used to evaluate the effects of prism (with/without), side (seeing/blind) and training (pre/post).
Patients had a trend to bias their eye-in-head position towards the blind side when wearing the prisms but not when walking without them (prism-by-side interaction p = 0.081). After training, there was a trend for patients to increase their head turns towards the blind side when wearing the prisms (prism-by-training interaction p=0.070). However, the overall distribution (standard deviation) of eye positions appeared to be narrower after training (from 12.7° to 11.2°, p=0.081) suggesting that there might be an environmental learning effect.
Preliminary results from this study suggest that peripheral-prism glasses may increase scanning toward the blind side in patients with hemianopia; recruitment is ongoing to increase the sample size.
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