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Matthew A Petoe, Samuel A Titchener, Mohit Naresh Shivdasani, James B Fallon, Carla J Abbott, Lauren N Ayton; Visual Scanning in Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1946. doi: https://doi.org/.
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Visual scanning using a co-ordinated combination of head and eye movements is critical to human vision. The propensity for head movement increases with age, and is assumed to increase more significantly in the case of progressive vision loss (e.g. retinitis pigmentosa, RP). This hypothesis has importance for the design of visual prostheses that aim to provide naturalistic control of gaze direction through eye-tracking. Therefore, in this study, we examined the oculomotor behaviour of normally sighted and RP subjects by analyzing the relative contributions of head and eye movements during several ocular motor tasks.
18 RP subjects (ages 31 – 84) and 17 healthy controls (ages 30 - 78) participated in the study. Each group was split into ages below 60 (8 RP, 7 controls) and above 60 (10 RP, 10 controls). The mean horizontal Goldmann kinetic visual field for RP participants was 37.3 ± 13.9° (age <60) and 18.8 ± 6.7° (age >60). Participants wore eye-tracking (Arrington Research Inc., AZ) and head-tracking (Ascension Technology Corp., VT) apparatus and performed head-free ocular motor tasks. Two measures of head movement tendency were extracted: the “customary oculomotor range” (COMR) during a pro-saccade task, i.e. the 95% range of eye eccentricities at the conclusion of gaze shifts to circular targets up to ±40° horizontal, where smaller COMR indicates narrower range of eye movement; and the “Head Gain”, i.e. head movement/(head + eye) ratio, where 1 = head only, 0 = eye only, during smooth pursuit of a circular target oscillating ±40° horizontally.
In the under 60 age group, there was no significant difference between RP and Controls in Head Gain (p = 0.19) or COMR (p = 0.094), Mann-Whitney U-test. In the over 60 age group, Head Gain was higher (p = 0.0017) and COMR was lower (p = 0.031) when comparing RP to Controls. This indicates that older RP participants had a significantly greater tendency for head movement during the tasks. There was a significant effect of age for all participants; Head Gain increased with age (p < 0.001 for RP, p = 0.043 for Controls), and COMR decreased (p = 0.0016 for RP, p = 0.0012 for Controls).
In comparison to healthy controls, loss of peripheral vision in older RP participants increases propensity for head movement during seated ocular motor tasks. The observed narrower range of eye movements is a consideration for the design of eye-directed visual prostheses.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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