Unequal narrowing of the visual field in a +Gz environment

Anecdotally, the existence of individuals who experience an unequal loss of peripheral vision (left versus right) under sustained +Gz acceleration is well known. However, there is little mention or explanation of the etiology in the literature. Only recently has there been a surge of interest in this phenomenon. The operational significance is more important. The most common interpretations for this phenomenon are unequal arterial pressure between the left and right blood supplies to the retina (ophthalmic artery, its branch to the retina, the central retinal arteries, the circle of Willis, and the internal carotid artery), and a difference in the intraocular pressure. Two case histories of unequal peripheral light loss (PLL) are discussed. It is possible for a pilot not to be aware of his or her full sequence of PLL and, in an operational environment, lose half the visual field and not realize it. We need more controlled studies to define unequal PLL and to ensure valid centrifuge subject data.