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Kimberly Meier, Miriam Spering, Deborah Giaschi; Fixation stability is not related to global motion deficits in amblyopia. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1026.
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© ARVO (1962-2015); The Authors (2016-present)
Observers with amblyopia have poor visual acuity in one eye. In addition to this hallmark deficit, these observers have unstable fixation in this eye when viewing stationary fixation targets, relative to healthy controls. Deficits in amblyopia have also been documented in global motion perception, especially at slow speeds. It is possible that poor fixation stability during motion viewing interferes with the fidelity of the input to direction-selective motion mechanisms. To investigate, we assessed motion coherence thresholds in observers with amblyopia while measuring fixation stability.
Participants with amblyopia (n = 14) and healthy controls (n = 15 younger adults, n = 15 older adults) conducted a two-alternative forced choice motion direction discrimination task (left, right) monocularly while fixating a central target. Coherence on each trial was controlled with a two-down, one-up staircase (stimulus duration = 600 ms). Two speeds of motion were assessed: slow (1 deg/s) and fast (30 deg/s). Eye movements were recorded with an Eyelink 1000+ eyetracker. Bivariate contour ellipse area (BCEA) was calculated on each trial as an indicator of fixation stability.
Consistent with prior work, participants with amblyopia had elevated coherence thresholds relative to controls for the slow speed task, but not the fast speed task. However, participants with amblyopia did not have poor fixation stability compared to controls for this task. Moreover, fixation stability during motion viewing was not correlated with coherence thresholds or with visual acuity in the amblyopia group or either control group.
Participants with amblyopia had normal fixation stability relative to controls, despite demonstrating deficient motion coherence thresholds on a slow speed global motion perception task. This work is the first to assess fixation stability in amblyopia during a global motion task, and indicates motion perception deficits are not a result of poor input to the motion processing system due to unstable fixation.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Coherence threshold in amblyopic viewers (23-65 ys) are significantly higher on the slow, but not the fast, global motion task compared to younger (20-30 ys) and older (31-65 ys) controls.
Log10 BCEA values when viewing motion stimuli at high and low coherence for both slow and fast speeds, as well as a control condition viewing stationary dots. There are no significant differences between groups.
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