Numerical Model of the Eye for Understanding Acute Microgravity-Induced Ocular Changes.

Abstract

Introduction: Intraocular pressure (IOP) changes with acute microgravity exposure defy easy explanation. IOP increases above supine levels acutely in weightlessness, but studies show both central venous pressure and intracranial pressure (ICP) fall below supine values. These reductions would be expected to reduce IOP in weightlessness. We developed and validated a physiologically relevant numerical model of the eye to investigate how these ocular changes could occur.

Methods: A finite element numerical model of the 50th percentile adult human globe, optic nerve, and surrounding tissues was constructed. The model incorporated 4 fluids and 12 different structures/tissues, with physical properties derived from the literature. The model included both hydrostatic gradients and tissue compressive forces, which are eliminated in weightlessness. We demonstrated model function using published clinical data from intravitreal injection and dark room provocation testing and then applied the model to predict acute microgravity-induced changes.

Results: Elimination of gx hydrostatic pressures increased episcleral venous pressure (EVP) at the eye and ICP at the lamina cribrosa despite overall reductions in central venous pressure and ICP compared to supine. IOP predictions were within 0.7 mmHg and 0.3 mmHg of experimental supine and parabolic flight values, respectively. A sensitivity analysis of factors increasing IOP showed a 0.75 mmHg increase from aqueous humor dynamics. Eliminating hydrostatic gradients produced a 0.55 mmHg increase from ICP and a 2.75 mmHg increase from EVP.

Discussion: The elevated IOP observed initially in short-duration microgravity may be caused by the loss of hydrostatic gradients and associated effects on EVP and ICP. Carroll DJ, Rothrock SA, Phillips SD, Knaus DA, Kattamis NT, Hayman APA, Fellows AM, Zegans ME, Buckey JC. Numerical model of the eye for understanding acute microgravity-induced ocular changes. Aerosp Med Hum Perform. 2026; 97(8):584-591.