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Lei Liu, Alex Keith, Mark Bolding; Smooth Pursuit Eye Movements with the Fovea, a Simulated Central Scotoma and a Real Central Scotoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4140.
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The quality of smooth pursuit eye movements is known to be affected by a textured background, the pursuit direction and the target velocity. Losing foveal input may interrupt smooth pursuit but the effects have not been well documented. This study compared smooth pursuit with the fovea (FOV), a simulated central scotoma (SCS) and a real central scotoma (RCS) under a wide range of conditions.
Ten young normal subjects and 6 patients with long-standing bilateral central scotomas visually pursued a target that moved along a 10 deg horizontal (H) or vertical (V) line over a uniform gray background (NB) or a binary random check background (TB). The speed profile of the target was a 0.15 Hz (S) or 0.40 Hz (F) sinusoid. Normal subjects performed 4-8 pursuits under each combination of background, direction and velocity with the fovea and with a 10 deg simulated central scotoma. Central scotoma patients did the same tasks with their impaired vision. Composite and smooth gains were computed using standard procedures.
SCS composite gain was the highest (1.17) while FOV and RCS composite gains (1.04 and 0.97) were similar. Although some of the differences were statistically significant, the composite gains under most conditions were above 0.9. FOV smooth gain (0.84) was better than those of RCS and SCS (0.54 and 0.42), indicating a significant reduction of pursuit quality when foveal input was cut off. Adding a textured background, pursuing in a vertical direction and increasing target velocity all significantly reduced composite gains, but the reductions were no greater than 0.1 under most conditions. The same stimulus changes reduced smooth gain more substantially. The highest smooth gains (0.95, 0.52 and 0.74 for FOV, SCS and RCS, respectively) were obtained with pursuing a slow target moving horizontally over a uniform background. They dropped to 0.68, 0.34 and 0.4 when pursuing a fast target moving vertically over a textured background (see figure). The type of background contributed the most to the observed smooth gain changes. SCS appeared to have suffered the smallest loss of smooth gains from the best to the worse pursuit conditions.
Composite gains are poor indicators of smooth pursuit deficits due to a central scotoma. Smooth gains obtained when pursuing a target moving fast in vertical direction over a textured background are more powerful measures of deficits.
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