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Rajkumar Nallour Raveendran, William R Bobier, Raiju J Babu, Benjamin Thompson; Interocular contrast differences and the stability of fixational eye movements. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3087.
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© ARVO (1962-2015); The Authors (2016-present)
The influence of binocular viewing on fixational eye movements is not well understood. This is important because abnormal fixational eye movements have been reported in disorders of binocular vision such as amblyopia. The objective of this study was to characterize the effect of interocular contrast differences on fixational eye movements in observers with normal binocular vision.
Adults with normal vision (n= 8) viewed stimuli constructed from a central bright fixation cross (1.2°) surrounded by a square (8.1°) presented on mean luminance background. Stimuli were presented dichoptically using a haploscope. Eye movements were recorded separately for each eye using an infrared eye tracker sampling at 500Hz. There were three experimental conditions: 1) The contrast of the target presented to non-dominant eye was fixed at 100% and the contrast presented to the dominant eye was varied from 0-100% contrast in octave steps. 2) The contrast of the target presented to dominant eye was fixed and non-dominant eye contrast was varied. 3) Contrast was varied from 5-100% in both eyes simultaneously. Each trial involved 30 seconds of fixation and each contrast combination was repeated 4 times. The stability of fixation was quantified separately for each eye using the global bivariate contour ellipse area (BCEA) method. Ocular dominance was estimated using a sighting test.
BCEA values were log transformed and subjected to repeated measures ANOVA. When the non-dominant eye contrast was fixed at 100% contrast, there was a significant interaction between Viewing Eye (non-dominant vs. dominant) and interocular contrast difference (7 levels) [F(6,42)=3.78;p=0.004]. This was characterized by significantly poorer fixation stability when the dominant eye had no central fixation cross (0% contrast) [BCEA=1.02 deg2] compared to the non-dominant eye [BCEA=0.70 deg2] (p<0.001). No differences between the two eyes were present for any other interocular contrast difference levels. Furthermore, no differences between the eyes were found when the dominant eye contrast was fixed at 100% contrast or when contrast was varied for both eyes.
Interocular contrast differences do not significantly influence fixational eye movements in normal observers. Contrast sensitivity differences alone may not underlie the poorer fixation stability observed in amblyopic eyes relative to fellow eyes.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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