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Vijay Patel, Frank A Proudlock, Irene Gottlob, Ophthalmology Group; Visualisation of two dimensional null regions in Infantile Nystagmus for functional and clinical use. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2658.
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© ARVO (1962-2015); The Authors (2016-present)
Head postures associated with infantile nystagmus (IN) often have horizontal, vertical and torsional components. We have developed a novel method to visualise null regions by mapping nystagmus waveforms at horizontal and vertical gaze angles for experimental and clinical use. The aim of the study was to use this method to characterise two dimensional (2D) null regions in IN and assess if they are accessed functionally during tasks of increasing visual demand.
Horizontal and vertical eye movements (EyeLink 1000) and roll, pitch and yaw head movements (InertiaCube motion tracker) were recorded in 20 participants with IN (10 with albinism, 7 idiopathic, 3 achromats) while performing tasks of increasing visual demand, i.e. eyes closed, fixation (with and without a mental maths task), reading (Radner reading test) and visual acuity (Landolt Cs). The head position during each task was compared to 2D null region maps generated by plotting the nystagmus characteristics (intensity and foveation) when fixating a target (head fixed), mapping out a grid covering a horizontal range from -30° to +30° and vertical range from 15° upwards to 30° downwards (in 7.5° steps). 2D null region maps were compared at two different distances (1.2m and 0.4m).
2D null region maps were observed in most participants, with nystagmus characteristics dramatically changing in vertical and horizontal planes. Horizontal and vertical head postures were used to access 2D null regions during tasks of higher visual demand with the result that absolute eye angles during head postures were significantly closer to null regions during the visual acuity task compared to the fixation (with and without a mental maths task) and eye closed tasks (p<0.05). A similar pattern was also observed during the reading task, however was only significantly different to the fixation with mental maths task (p<0.05). 2D null regions changed considerably for most participants between the two viewing distances (0.4m and 1.2m).
These findings demonstrate that 2D null region mapping provides a useful way of visualising the null region in IN that is functionally relevant and comprehensively describes the null region in horizontal and vertical planes. This method may by an effective way of objectively measuring changes in null region characteristics brought about by interventions such as surgical and pharmacological treatments.
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