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Hilary Ann Hamer, Andrew McLeod, Athanasios Panorgias; Binocular Interactions during Rapid Alternating Occlusion as measured with Visual Evoked Potentials. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
Rapid alternating occlusion (RAO) is used to treat amblyopia. The neural mechanism, however, is not well studied. To test the neural interactions during RAO, we measured Visual Evoked Potentials (VEPs) under different dichoptic conditions.
Subjects (n=5) underwent an eye screening and had no history of ocular pathologies, refractive error less than 5.00D sphere and/or 2.50D cylinder and no anisometropia greater than 0.75D. 9mm gold-cup electrodes were positioned according to the International 10/20 system for recording VEPs. Electrophysiological responses were digitized using the Espion v6 suite (Diagnosys LLC, MA). Stimuli were presented using a mirror stereoscope with subjects fixating on a cross while dichoptically viewing two neutral-grey 10° diameter disks (100 cd/m2) presented against a neutral background (50 cd/m2). Three experiments were performed by each subject. On the first experiment the disks were presented to just one eye at frequencies between 4 and 35 Hz. On the second experiment the disks were alternatively presented to each eye at the same frequencies. On the third experiment the disks were alternatively presented to each eye at 7Hz while we introduced an onset delay in one of the two disks ranging from 10 to 71ms. Recordings were Fast Fourier Transformed. ANOVA and two-tailed Student’s t-tests (α=0.05) were used to compare frequencies and amplitudes of first and second harmonics (H).
The results of the monocular experiment showed that the amplitude of the 2nd H was equal to the amplitude of the 1st H for frequencies lower than 8Hz (p=0.69). During binocular dichoptic viewing the amplitude of the 2nd H was higher than the amplitude of the 1st H for alternating frequencies up to 8Hz with a peak at 7Hz (p=0.019). The results of the third experiment showed that the amplitude of the 2nd H is higher for interocular delays less than ~20ms (p=0.037) and longer than ~40ms (p<0.001) with a trough between 30 and 40ms.
The difference in amplitude of the 2nd H between the first and the second experiment indicates that the 2nd H of the second experiment reflects enhanced binocular activity for alternating frequencies between 6 and 8Hz. The increased 2nd H amplitude for interocular delays below 20ms can only be explained by binocular summation. This series of experiments offers the first evidence that RAO promotes binocular interactions based on VEP results.
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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