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Rebecca J McLean, Vijay Patel, Irene Gottlob, Frank A Proudlock; Head movements during reading in infantile nystagmus. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5104.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that horizontal (yaw) head movements are normally suppressed during reading tasks to improve stability of fixation. In infantile nystagmus (IN) yaw head movements may serve a purpose during reading in maintaining eye angles in the null region. The aim of this study was to compare the amplitude of yaw head movements in IN to controls during a reading task and a horizontal smooth pursuit task. We have investigated the relationship between yaw head movement amplitude during reading and the null region depth.
Horizontal and vertical eye movements (EyeLink 1000) and roll, pitch and yaw head movements (InertiaCube motion tracker) were recorded in 16 participants with IN (10 with albinism, 4 idiopathic, 2 achromats) and 15 controls when reading a paragraph of text covering visual angles of ±19° horizontally and ±10° vertically (distance 0.6m). The smooth pursuit task consisted of a target following a trapezoid profile of ±15° moving at a linear velocity of 20°/s (turnaround=300ms). Yaw head movement amplitudes during reading in IN were compared to the range of nystagmus intensities observed along the horizontal plane (from -30° to +30° in 7.5° steps) where the null was located.
Participants with IN made significantly greater head movements compared to controls during both the reading task (median amplitudes 4.19° and 0.069°, respectively, p<0.0001) and the smooth pursuit task (median amplitudes 1.16° and 0.027°, respectively, p=0.0062). There was a significant correlation between yaw head movement amplitudes during reading in IN participants and the nystagmus intensity range along the horizontal plane (R=0.75, p=0.001).
These findings demonstrate that individuals with IN can use head movements adaptively to assist reading by maintaining the eye angles in the null region. Yaw head movements are especially useful for individuals with IN who have deep null regions where more intense nystagmus outside of the null region is likely to cause deterioration in reading performance. The larger yaw head movements observed during the smooth pursuit task for individuals with IN may suggest that individuals with IN develop a larger head movement propensity than controls possibly through persistent use of head movements to aide visual function.
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