Pupil size and microgravity: A study in parabolic flight

Abstract

In five test subjects the effect of the otolith stimulation on pupillary size was observed during short lasting periods of microgravity during parabolic flight. Continuous pupil observations of one eye were made with a videocamera. In most cases microgravity gave a pupil dilatation, while during periods of increased G-load a pupil constriction was seen. These results confirm earlier findings.

An explanation of these findings can be given by the assumption of connections between the vestibular nuclei and both the pretectal area and the Edinger-Westphal nucleus, from where parasympathetic and sympathetic fibers originate to regulate the pupil size. Such pathways have been described before in cats and monkeys. This should mean that a vestibulo-pupillary reflex mechanism exists.

Key Words:

• pupil size
• pupil dilatation
• pupil constriction
• microgravity
• increased G-load
• vestibulo-pupillary reflex