EXTENDED REPORT

Interpreting the multifocal visual evoked potential: the effects of refractive errors, cataracts, and fixation errors

B J Winn¹, E Shin¹, J G Odel², V C Greenstein² and D C Hood¹

¹ Department of Psychology, Columbia University, New York, USA
² Department of Ophthalmology, Columbia University, New York, USA

Correspondence to:
Correspondence to:
D C Hood
Department of Psychology, 405 Schermerhorn, Columbia University, New York, NY 10027, USA; dch3{at}columbia.edu

Aim: To understand how refractive errors, cataracts, and fixation errors affect multifocal visual evoked potential (mfVEP) responses.

Methods: Monocular mfVEP responses were obtained using a pattern reversal dartboard display. For the control condition, visual acuity was corrected to 20/20 and foveal fixation was maintained. The right eye was tested under the following conditions: simulated refractive error, simulated cataract, steady eccentric fixation, and unsteady fixation.

Results: No subject demonstrated significant abnormalities under control conditions. For the simulated refractive error condition, significant centrally located abnormalities were seen for all subjects. For the simulated cataract condition, significant abnormalities were found for three subjects. The steady eccentric fixation condition yielded abnormalities in both eyes for all subjects while the unsteady fixation condition yielded significant central abnormalities in the tested eye. With eccentric and unsteady fixation conditions, all subjects had at least one sector with a waveform polarity reversal.

Conclusions: While the mfVEP is a useful tool for identifying local optic nerve damage or ruling out non-organic aetiology of visual field defects, factors such as uncorrected refractive errors, cataract, eccentric fixation, and unsteady fixation can produce apparent field defects on the mfVEP. With care, these problems can be correctly identified.

Abbreviations: mfVEP, multifocal visual evoked potential; RMS, root mean square; SNR, signal to noise ratio; VEP, visual evoked potential

Keywords: visual evoked potential; refraction; fixation

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