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A. Martins, C. Balachandran, A. Klistorner, S.L. Graham; Effect of Pupil Size on Objective Perimetry using Multifocal Visual Evoked Potentials . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4118.
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Purpose: The purpose of this study was to investigate the influence of pupil diameter on the amplitude and latency of multifocal visual evoked potentials (m-VEP). Methods: The multifocal objective perimeter (AccumapTM; Objectivision) was used to stimulate the visual field at 56 sites extending to 32° using a pseudorandom pattern stimulus. M-VEPs were recorded using bipolar occipital electrodes, 7 min/eye. Ten normal subjects were recruited from the community and one eye was randomly selected for testing. M-VEPs were recorded at four different pupil diameters (2mm, 4mm, 6mm, 8mm), obtained by applying tropicamide (0.5%) or pilocarpine (2%) in different dilutions. Appropriate refractive correction was provided to overcome cycloplegia and achieve a visual acuity of 6/7.5 or better. Results: Analysis revealed that at most pupil diameters the normalized full field amplitude did not show significant variation, except at the most miotic pupil diameter (2mm), where the amplitude became reduced, based on ANOVA, Randomised Block Design (RBT) and Tukey’s T Method. There was however, significant correlation between latency and pupil area (corr coeff, upper field –0.63, and lower field –0.76). Conclusions: The above results suggest that even in the presence of mydriatics or miotics, the m-VEP test can be used to assess diseases that affect amplitude, provided near correction is used. The interpretation of latency, however, must be made with caution, as a borderline conduction defect with a dilated pupil may appear normal.
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