PATTERN-ONSET VISUAL-EVOKED POTENTIALS - MORE USEFUL THAN REVERSAL FOR PATIENTS WITH NYSTAGMUS

Purpose: The visual evoked potential is often used to assess visual fu nction in neurologically impaired patients, a group in whom nystagmus is a common feature. Pattern-reversal stimuli are commonly used to pro duce visual evoked potentials in clinical practice. Previous reports h ave shown that this stimulus is not optimal when subjects have nystagm us. The present study aimed to compare the efficacy of pattern-onset a nd reversal stimuli when used to measure visual evoked potentials from subjects with idiopathic nystagmus. Methods: In five adults with cong enital nystagmus and 10 visually normal adults, VEPs were recorded and reproduced for checkerboard stimuli of two sizes (120' and 60'). Each size was presented as both pattern-onset and reversal check. Results: Visually normal adults demonstrated similar visual evoked potential a mplitudes and quality in response to pattern-reversal and pattern-onse t. However, in the presence of nystagmus, visual evoked potentials rec orded to pattern-reversal stimuli were significantly smaller and of po orer quality than those obtained to pattern-onset stimuli (analysis of variance p<0.05; Kendall's tau, p<0.05). Conclusions: Pattern-onset s timuli produce larger and clearer visual evoked potentials in patients with nystagmus compared with those produced to pattern-reversal stimu li.