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B.J. Winn, E.H. Shin, V.C. Greenstein, J.G. Odel, D.C. Hood; Interpreting the Multifocal Visual Evoked Potential (mfVEP): The Influence of Cataracts, Refraction and Fixation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):32.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To understand how cataracts, refraction and fixation patterns affect multifocal visual evoked potential (mfVEP) responses. Methods: Monocular mfVEP responses were obtained from both eyes of five subjects with no known visual abnormalities using a pattern-reversal dartboard display (44.5° dia) containing 60 sectors. Visual acuity was corrected to >= 20/20 and foveal fixation was maintained. The right eye was tested under the following conditions: control, visual acuity reduced optically to 20/30, to 20/50, simulated cataract (0.4 occlusion foil), steady fixation 3º inferonasal to the fovea, and unsteady eccentric fixation (3° radius) around the fovea. Interocular, monocular and waveform analyses were performed on the mfVEP responses [1,2]. Probability plots, analogous to the probability plots of the Humphrey Visual Field Analyzer, were used to identify mfVEP abnormalities. A region was classified as abnormal on a cluster test [e.g. 2,3], if 2 or more contiguous points were significant at <1% or 3 or more contiguous points were significant at <5%, with at least one at <1%. Results: Using interocular analysis, significant central abnormalities were seen for 3 subjects for the 20/30 condition, and for all subjects for the 20/50 condition. Predominantly central abnormalities were found for 2 subjects for the simulated cataract condition. Unsteady eccentric fixation produced clear central abnormalities while steady eccentric fixation yielded abnormalities in both eyes for all subjects. These steady eccentric fixation errors can be identified as they respect an axis perpendicular to the direction of eccentricity. Using monocular analysis, abnormalities were detected for 3 subjects under unsteady and steady eccentric fixation conditions. Abnormalities were not detected for 20/30, 20/50 or simulated cataract conditions for any subject using monocular analysis. Four subjects tested under unsteady, and all subjects tested under steady, eccentric fixation conditions had at least one sector with waveforms that were reversed in polarity while no subject exhibited waveform reversals under 20/30, 20/50 or simulated cataract conditions. Conclusions: The mfVEP can identify local optic nerve damage or rule out non-organic etiology of visual field defects. However, factors such as uncorrected refractive errors, cataract, eccentric or unsteady fixation  can produce apparent mfVEP deficits. With care, these problems can be identified. 1. Hood et al (2002) AO. 2. Hood & Greenstein (2003) Prog Ret Eye Res. 3. Goldberg et al (2002) AJO. 4. Menz et al (2002) ARVO.
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