A Case of Voluntary Nystagmus.

In most cases, nystagmus develops as a physiological or pathological reflex. However, cases of voluntary nystagmus have been reported.A 14-year-old boy complained of several attacks of dizziness with nausea. He could induce voluntary nystagmus and demonstrated this to us. Since 9 year of age he has been able to induce nystagmus in frontal gazing. His nystagmus was pendular jerky. Amplitude was 5-10 degree and the frequency was 6-7 Hz. Nystagmus could be sustained for more than 1 minute. The nystagmus did not diminish and was not limited by fatigue. We observed no nystagmus in gazing. Neither positional nystagmus nor positioning nystagmus was noted. Although the horizontal eye movement was slightly saccadic, the vertical eye movement was smooth. Optokinetic nystagmus was not well developed and showed partial inversion. Convergence was possible and latent nystagmus was not observed. Nystagmus as assessed by a caloric test was well developed. No abnormal neurological findings were indicated and MRI imaging revealed no lesion.Since William's first study was reported in 1865, many cases of voluntary nystagmus have been documented. Voluntary nystagmus is usually described as being of a high frequency and low amplitude. The duration is brief, less than 30 seconds, and limited by fatigue. In most cases, nystagmus is pendular and is sometimes jerky.We divide cases of voluntary nystagmus, which were examined by an optokinetic nystagmus (OKN) test, into two groups. One group showed a normal OKN pattern, which was described as typical voluntary nystagmus, and the other group showed an abnormal OKN pattern similar to congenital nystagmus. Our case was classified in the abnormal OKN group. In this case, nystagmus which is usually latent develops when the patient cannot control his eye movements or when he does so voluntarily.