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D.S. Nicol, D.L. McCulloch, U. Shahani, V. Manahilov; Visual Evoked Potentials (VEPs) to Sinusoidal Flicker in Amblyopic Subjects . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3600.
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Purpose: Amblyopia is characterised by deficits in spatial resolution and localisation while temporal resolution may remain largely unaffected. We recorded VEPs to monocular and binocular luminance modulation across a range of temporal frequencies for comparison in amblyopic and control subjects. Methods: Five amblyopic subjects (interocular difference of VA greater than 0.1LogMAR, stereoacuity less than 60’’) were compared with six control subjects (VA 0.00 LogMAR or better each eye, stereoacuity 60’’ or better). VEPs were recorded to full field sinusoidally modulated flicker presented in an LED Ganzfeld stimulator at 10 stimulus frequencies between 3Hz and 60Hz. Electrode sites were; Oz, O3, O4 and Pz. Right eye, left eye and binocular recordings were made in a random order. A light occlusive eyepatch was used for monocular testing. Off line Fourier transform was used to record the steady state VEP amplitudes at the fundamental (F1), double (F2) and triple (F3) harmonics of the stimulus frequency. Results: For Oz, both binocular and monocular F1 amplitudes were optimal between 7–21Hz while F2 and F3 amplitudes peaked at lower stimulus frequencies. At each harmonic, monocular VEPs from the amblyopic subjects did not differ significantly between eyes, or from the VEPs of the control eyes, across the range of stimulation frequencies. Additionally, amblyopic subjects showed no significant interocular differences for any stimulus condition or harmonic. However, control subjects were found to have greater binocular summation of VEPs compared with amblyopic subjects across all frequencies of stimulation, and all harmonics (p=0.01) Conclusions:There were no interocular differences in sinusoidal flicker VEPs between amblyopic and fellow eyes. Amblyopic subjects have reduced binocular summation of VEPs to temporal modulation when compared to control subjects.
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