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 elec tronystagmographic registration of optokinetic nystagmus. The aim of this s tudy was to replace the Subjective methods used previously with a more reli able quantitative technique and thus assess ophthalmoplegy and diplopia, im portant initial symptoms in MG. Slow phase angular speed values of foveolar type optokinetic nystagmus in the horizontal plane at 10, 20 and 30 degree s/s target speed were determined. Measurements were performed before and af ter administration of Mestinon, a reversible cholinesterase inhibitor. Twel ve healthy volunteers were examined as controls under standard conditions. Results showed significant differences between MG patients and control grou p. Slow-phase angular speed was significantly larger after Mestinon adminis tration (p < 0.001). It is concluded, that the exhaustion of external ocula r 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.