Limitation of ocular motility and pupillary dilatation in human beings during positive acceleration.

During positive acceleration in man, a stage is reached at which there is a limitation of ocular motility. These limitations can be overcome by voluntary effort, but the superseding movements are ataxic. The lower motor neurons to the extraocular muscles are not involved in LOMA. The pupils dilate as the visual fields constrict during positive acceleration and reach a maximum luith loss of central vision. The optokinetic reflex does not continue during blackout. However, a form of horizontal nystagmoid movement of the globes may persist in eyes previously stimidated by the optokinetic drum. Vertical nystagmus is observed during high rates of change of positive acceleration. With a modified skin diver's mask, 30 mm. Hg of negative pressure was applied to the orbit, and under these conditions vision was restored, ataxic voluntary movements became coordinated, optokinetic reflexes were restored to their original frequency, and the pupils remained partially dilated. The pupillary dilatation which accompanies blackout is prevented by the local application of pilocarpine and is unaffected by morphine. The observation of LOMA is a useful objective end point for the evaluation of response to positive acceleration. The observation of pupillary dilatation is a useful quantitative sign for evaluation of response to positive acceleration.