The potential influence of sleep on translaminar pressure dynamics and ocular glymphatic outflow in microgravity: implications for optic disc edema in astronauts

The authors nicely discuss a recent study by Christian et al. [2] in a spaceflight analogue comprising 30 days of strict 6° head-down tilt bed rest (HDTBR) in the setting of mildly elevated carbon dioxide levels. This study found that subjects who developed optic disc edema (ODE) were more likely to have short sleep duration and a blunted circadian temperature amplitude [2]. Given that the brain glymphatic system is primarily active during sleep, Nguyen et al. [1] noted that one possible explanation for the association of impaired sleep with the development of ODE could be that sleep deprivation may impair the clearance of metabolic waste from the optic nerve region through disruption of the ocular glymphatic system. Here, we provide an additional alternate explanation.