Visual suppressibn test に及ぼす眼位の影響

正常者と脊髄小脳変性症患者における検討

抄録

Caloric tests were performed in 38 normal volunteers and 63 patients with spinocerebellar degeneration (SCD).
1) Maximum slow phase velocity of caloric nystagmus in darkness (SPV-max), 2) visual suppression of caloric nystagmus (VS) and 3) tonic deviation of the eyes in darkness just before a light was put on for visual supression (D) were measured from electronystagmographic recordings. D was defined as positive when the eyes deviated to the side of cold water irrigation and negative when the eyes deviated to the opposite side.
1. Normal and SCD groups showed almost the same SPVmax value.
2. The SCD group showed a lower VS value than the norm-al group (p<0.005).
3. The mean value of D was positive in the SCD group, i.e. the eyes deviated to the side of cold water irrigation. In the normal group, it was also positive, but deviation was smaller than in the SCD group (p<0.025).
4. SCD patients with gaze nystagmus showed a lower VS value than patients wIthout gaze nystagmus (p<0.005).
5. Some SCD patients without gaze nystagmus showed a low VS value (≤ 30%).All of these patients showed a high D value (≥ 14°).
6. Although some normal subjects showed a high D value, they all showed a normal VS value.
A large D could represent a poor VS in some of the SCD patients, because, aecording to Alexander's law : the slow phase velocity of vestibular nystagmus is less when the eyes are deviated to the side of the slow phase. The present study confirms that a low VS value definitely indicates impairment of the central vestibular system even if the eyes are deviated to the side of the slow phase.