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Lee Mcilreavy, Tom CA Freeman, Jonathan T Erichsen; Two dimensional analysis of horizontal and vertical pursuit performance in infantile nystagmus. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2914. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies of pursuit in infantile nystagmus (IN) have generally overlooked the ability to pursue targets moving vertically, presumably because the oscillation accompanying IN is predominantly horizontal. We compared horizontal and vertical pursuit in IN and controls, in each case analysing both the horizontal and vertical components of the eye movements in order to obtain 2D performance measures.
Fifteen adult participants with IN completed a monocular pursuit task, with normally sighted age-matched participants as a control. Horizontal and vertical pursuit was to a 0.2° green dot moving through primary position with a total excursion of 16° or 32° at velocities of either 8°/s or 16°/s. Eye movements were recorded at 1000Hz (EyeLink 1000) and analysed offline. After removing saccades and fast phases (IN), eye velocity relative to the pursuit target was used to obtain 2D probability density functions. Isocontours bounding 68% of the highest probability densities estimated velocity matching. Accuracy was defined as isocontour centre of mass, while precision was defined as isocontour area. Principal component analysis of isocontour bounded data yielded major and minor axes of the area and its shape.
Results to date indicate pursuit precision was significantly lower along both orientations for IN compared to controls (vertical p<0.001, horizontal p<0.001). While the IN group showed large variation, especially for accuracy, horizontal pursuit precision was significantly greater than vertical (p<0.001) for IN, with no significant difference in controls. Isocontour area was significantly more circular for vertical than horizontal pursuit (p<0.001) for both IN and controls. Further analyses of IN data may reveal the influence of the null zone, if any, on velocity matching during pursuit as well as the role of fast phases in re-establishing pursuit.
We present a novel method for investigating IN slow phase velocity matching to a pursuit target. Our results suggest that pursuit performance in IN is neither accurate nor precise when compared with controls, with significant impairment for vertical pursuit compared with horizontal.
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