視運動性眼振の正常反応とこれに影響する因子

抄録

In order to clarify the properties of optokinetic nystagmus (OKN), optokinetic response was recorded by DC-ENG in 14 healthy young adults, to whom constant speed stimulations (20-120-/sec) were administered using an Ohm's rotatory drum. The OKN obtained was analysed quantitatively and qualitatively. Among the factors considered to influence nystagmus response, the condition of stare and focus, the direction of vision, the number of stripes on the drum, age, and abnormality of visual field were studied. The following results were obtained.
(1) In normal OKN response, the frequency of the nystagmus coincided with the number of stripes which passed before the eyes up to * drum speed of 120-/sec. The speed of the slow phase of nystagmus was in direct proportion to drum speeds up to 75-/sec, but tended to increase in lesser proportion at higher drum speeds of up to 120°/sec. The amplitude of nystagmus was 39±7° at a drum speed of 20°/sec and decreased with an increase of drum speed. The initial phase of the optokinetic response was a slow eye movement corresponding to
thedirection of drum rotation. Although the field of nystagmus often deviated from the median to the direction of the rapid phase, it was reversible to the direction of the slow phase by strengthening the degree of fixation.
(2) The nystagmus responses by a stare and a look test were compared. It was found that the co-existence of stare and look should be avoided, if an accurate quantitative analysis was to be obtained, and that the look test should he regarded as the standard.
(3) There was no difference in frequency and amplitude between 20- lateral gaze and straight gaze. The speed of the slow phase was, to some extent, lower in the lateral gaze than in the straight gaze.
(4) There was no difference between 8 and 12 black stripes in the quantitative relationship between stimulations and responses.
(5) Normal values of OKN obtained from young adults could he adopted for individuals in their fifties.
(6) When there was concentric narrowing up to 15°or central scotoma up to 5° in the visual field, the speed of the slow phase of OKN decreased, but there was no abnormal wave pattern. However, in a case with the narrowed visual field up to 5°, the fixation by the rapid eye movement to a stripe appeared in the visual field became inadequate and the eyes tended to return to the median position. During the slow phase the eye movement delayed from the moving object, which was supplemented by saccade. These results showed that the perifoveal region (5-15 degrees) of the retina played an essential role in the development of OKN.