[Characteristics of optokinetic, opto-oculomotor and vestibulo-oculomotor reactions in weightlessness]

Abstract

Investigations of spontaneous and evoked optokinetic, optooculomotor, and vestibulooculomotor reactions in microgravity are described. The investigations were performed during the 7-day Soviet-Indian flight and during the 237-day Salyut-7 flight. At an early period of adaptation to microgravity spontaneous oscillations of the eyeballs were enhanced: spontaneous nystagmus (in one of the subjects), lower effectiveness of saccadic pursuit (saccade elimination during the pursuit of a moving target, decrease of saccade amplitude, appearance of corrective microsaccades during fixation turns and pursuit), decline of the optokinetic nystagmus threshold. Compensatory eye counterrotation, when the head moved from side-to-side in the frontal plane with eyes open and dark glasses on, did not disappear but attenuated slightly; it was followed by low amplitude nystagmus. When the head moved with eyes open, one of the crewmembers showed complete eye destabilization while others--high amplitude nystagmic oscillations. When the head turned around with eyes open, clonic nystagmus occurred.