Electronystagmographic analysis of optokinetic nystagmus for the evaluation of ocular symptoms in myasthenia gravis.

Ocular symptoms of 17 myasthenia gravis (MG) patients were examined by electronystagmographic registration of optokinetic nystagmus. The aim of this study was to replace the subjective methods used previously with a more reliable quantitative technique and thus assess ophthalmoplegia and diplopia, important initial symptoms in MG. Slow phase angular speed values of foveolar type optokinetic nystagmus in the horizontal plane at 10, 20 and 30 degrees/s target speed were determined. Measurements were performed before and after administration of Mestinon, a reversible cholinesterase inhibitor. Twelve healthy volunteers were examined as controls under standard conditions. Results showed significant differences between MG patients and control group. Slow-phase angular speed was significantly larger after Mestinon administration (p < 0.001). It is concluded, that the exhaustion of external ocular muscles in MG can be well characterized by the determination of the slow phase angular speed values of optokinetic nystagmus (OKN). The examination of OKN was also recommended for the evaluation of ocular symptoms in other neurological disorders.