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Gro Horgen Vikesdal, Trine Langaas, Stuart J Gilson; Recording of eye movements; with or without glasses?. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2561.
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The purpose of the study was to determine the effect of induced refractive error on saccades and fixation. Decreased latency, poor saccadic control and fixation instability have been found in patient groups that have an increased prevalence of accommodative disorders. If eye movement studies do not control for accommodative status nor visual blur, possible contamination of results may occur. This study aimed to clarify the degree to which blur or accommodative stress might influence performance in eye movement tasks.
14 young adults aged 20-39 with normal visual function participated in the study. They performed saccade- and fixation tasks, while their eye movements were recorded using a fast video-based eye-tracking system. Stimulus was a bright dot, subtending 0.2°, presented on a dark screen at a distance of 100 cm. The tasks started with the appearance of a fixation cross followed by the appearance of the stimulus in random positions, 5° from the fixation cross, repeated 40 times. The tasks were performed with 6 different contact lenses, to induce blur and accommodative stress. All participants were tested wearing best spherical correction (control lens), and then an addition of +3.00, +1.50, -1.50, -3.00 and -5.00.
Raw eye position data were classified into saccades (velocity >20°/s) and fixations (velocity <20°/s). Mean saccadic latency for the control lens was 208 ±18 ms and this was significantly different from the -1,50 lens, although the differences were small, ranging from 1-12 ms. None of the other lenses had a statistically significant effect on saccadic latency. Mean peak velocity for the control lens was 63±12 °/s, and there were no significant differences between the lenses. Mean fixation stability for the control lens was 388±188 (Bivariate Contour Ellipse Area), and there was a tendency to less stable fixation as the power of the lenses increased, but no significant differences were observed.
For healthy young adults with no accommodative disorders, induced refractive error with powers ranging from +3.00 to -5.00 did not have a substantial effect on either saccadic latency or peak velocity. Fixation stability remains the same with all the lenses. While it remains good scientific practice to correct-to-normal participants in eye movement studies, this study has shown that the human visual system is tolerant to induced refractive error under these conditions.
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