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Arvind Chandna, Ian Cunningham, Laura Renninger; Unusual responses to disruption of fusion are revealed with objective eye tracking: all is not what is seen. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4092. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Determine the potential of objective eye tracking, under normal viewing environment, to capture subtle and curious responses to the transient disruption of binocular fixation, subsequent recovery of binocular alignment and adaptation to the continuing presence of the disruption
5 experienced subjects (Mean±SD=30.8±13.5yrs) participated. Eye movements were recorded via infrared oculography using an eye tracker (Tobii TX300, Tobii Technology AB, Sweden) using 2 clinical tests: 1) Cover Test (CT) using a modified occluder (infrared-transparent) in order to track the covered eye. 2) 20Δ Base-Out prism test (20BO) was placed in front of the right eye causing a fixation disparity.
4 subjects had well-controlled exophoria (Prism&CT: Range 14Δ to 6Δ). Latent eye deviations were not significantly different between right and left eye on cover/uncover test (RE: 15.13±13.31units LE: 12.72±10.16units p=0.38). There was a small, statistically insignificant, increase in deviation size on alternate cover testing (RE: 18.53±17.84units, LE:18.59±15.81units, p=0.49). On introduction of the 20BO, the right eye moved inwards by 114.60±44.37 units, driving the left eye outwards by 7.60±29.00 units (t=4.54, df=8, p=0.00009). On removing the prism, right eye moved outward by 71.40±46.00 units and left eye 7.60±29.00 units (t=1.92, df=8, p=0.045). For both CT and 20BO, patterns of recovery were different between subjects: monocular fusional vergence and binocular version-monocular vergence movements.
Objective CT using our modified occluder enabled the study of eye movements behind the cover. CT and 20BO revealed new and unique aspects of sensori-motor oculomotor responses to disruption of fusion. Traditional understanding of oculomotor responses to disruption of fusion needs to be revised. Differences seen are likely to be related to individual panum’s fusional areas indicating an economy and efficiency of eye movements to disruption of fusion. Differences in recovery patterns seen may indicate latent deviations that are likely to decompensate to manifest deviations It is hoped further testing will show interactions between fragile binocular functions and other unusual eye motility.
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