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Stuart G Coupland, Lynca Kantungane, John Hamilton, Rustum Karanjia; The effect of simulated pendular nystagmus on pattern-reversal and pattern-onset VEPs. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4895.
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Pattern-reversal visual evoked potentials (PR-VEP) are an important tool for objective assessment of visual function. In patients with oculomotor instabilities who cannot maintain steady fixation due to nystagmus the PR-VEP can be significantly reduced in amplitude. Although Pattern-onset VEPs (PO-VEP) have markedly higher interindividual variability than PR-VEPs they are preferred in special situations such as diagnosis of albinism or for patients with nystagmus. The aim of this study was to quantify the effects of simulated horizontal pendular nystagmus on PR-VEP and PO-VEPs in normal subjects.
Twenty eyes of 10 visually normal subjects were assessed on pattern-reversal and pattern-onset VEPs of 60 and 15 minutes checksize. VEPs were recorded from occipital midline according to ISCEV standards under monocular stimulation. A reversal rate of 2 Hz was used for pattern-reversal VEPs and pattern-onset VEP presentation rate of 200 msec onset and 400 msec offset was used. Simulated pendular nystagmus was produced by superimposition of a horizontally moving fixation target over the 15 degree checkerboard pattern stimulus subtending 5 degrees either side from central fixation.
Simulated pendular nystagmus significantly decreased PR- VEP amplitude by a mean reduction of 60% (p<0.05) for both 60 and 15 minute checksizes compared to PO-VEP amplitude reduction of 25% (ns). There was no significant effect of eye movement on PR-VEP or PO-VEP timing.
Pattern-onset stimulation with simulated pendular nystagmus supports previous reports on PO-VEPs in nystagmus patients. It is likely that motion-induced image blur is responsible for PR-VEP amplitude reduction.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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