Use of a stenopeic semiocclusor enhances vep diagnosis

We conducted a study to assess the capability of a 2-mm stenopeic semiocclusor in improving the sensitivity of the standard full-field pattern-visual evoked potential technique to disclose abnormalities of the pre-chiasmatic visual pathway.

Nineteen control subjects and fifty-five patients with a diagnosis of definite or probable Multiple Sclerosis (MS) were evaluated. All subjects were seated in front of a 19" TV monitor depicting a black and white square pattern, standard condition (R). Two trials of 100 stimulus repetitions at 1.8 Hz, recording at Oz- Fz were performed for each eye. After two minutes the procedure was replicated using an stenopeic semiocclusor, central field condition (S). The main parameters quantified were the P100 latency in each eye (a) and P100 inter-ocular difference (b).

Under condition R abnormalities were detected in 42 patients for parameter "a", and in 39 patients for parameter "b". If both parameters, a + b, were considered 48 patients (87%) showed abnormalities. Under condition S, abnormalities were detected in 49 patients for parameter "a" and 41 patients for parameter "b". When both parameters, a + b, were considered 53 patients (96%) showed abnormalities.

The main point of interest of this study is the fact that when a pattern reversal stimulus is restricted to the central area the evoked response shows a P100 peak with prolonged latency in comparison to the full-field stimulus. Additionally, used in combination with the standard full-field technique it improves the abnormality detection rate whilst adding little extra time to the procedure.