To the Editor We very much appreciate the article recently published in JAMA Ophthalmology by Laurie et al.1 The authors reported that the development of optic disc edema (ODE) was greater in individuals participating in a spaceflight analog study in which participants underwent 30 days of strict 6° head-down tilt bed rest than astronauts experiencing a similar duration of actual spaceflight. Conversely, peripapillary choroid thickness increased during spaceflight but not in individuals participating in bed rest. The authors concluded that elucidation of these differences will provide new insight into the mechanisms of ODE in astronauts. Here, we raise the question of whether intraocular pressure (IOP) may be one factor that can at least partially explain the different severity of ODE between the cohorts.