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Kristina Irsch, Robert B Geary, Jing Tian, David L Guyton, Boris I Gramatikov, Howard S Ying; Interocular fixation instability: a sufficient marker for amblyopia?. Invest. Ophthalmol. Vis. Sci. 2014;55(13):813.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether detection of interocular fixation instability may serve as a single sensitive test for amblyopia.
Binocular eye movements were recorded at 500 Hz using the EyeLink 1000 eye tracker (SR Research Ltd., Ontario, Canada) and analyzed using EyeLink software and Matlab (Mathworks, Natick, MS). Eight subjects (three non-amblyopic and five amblyopic including one successfully-treated amblyope; age: 7-44 years) were asked to fixate on a cross subtending 0.5° at a distance of 57 cm. Interocular fixation stability was quantified by calculating the minimum-area bivariate contour ellipse (BCEA) encompassing 68% of the difference between right and left eye fixation points during a 20-second binocular viewing epoch. For statistical analysis, BCEA values were normalized by a common logarithm transformation.
The amblyopic subjects with persistent vision loss (one anisometropic, two strabismic, and one deprivation; uncorrected visual acuity range 20/60-20/300) showed significantly higher interocular fixation instability (larger 68% BCEAs) than the non-amblyopic subjects (uncorrected visual acuity range 20/20-20/800), and the successfully-treated strabismic amblyope (to the 20/20 level of visual acuity); p < 0.01.
Based on our results, interocular fixation instability differentiates amblyopic from non-amblyopic subjects and improves after successful treatment. Interocular fixation instability may therefore prove to be a single sensitive test for the presence of amblyopia. As a difference measure, it is less susceptible to head motion and calibration error, as well as to conjugate eye motion, and as such is expected to be somewhat immune to latent nystagmus. Interocular fixation instability may also be used to guide treatment, especially in preverbal children and to assess the efficacy of novel treatments. Further research is required to establish optimal interocular fixation instability thresholds and to determine how specific this measure is to amblyopia.
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