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

Area of Science:

• Ophthalmology
• Aerospace Medicine
• Biomedical Engineering

Background:

• Intraocular pressure (IOP) changes unexpectedly during acute microgravity exposure.
• Despite falling central venous pressure and intracranial pressure (ICP), IOP rises in weightlessness.
• Existing data contradicts expected physiological responses, necessitating further investigation.

Purpose of the Study:

• To develop and validate a numerical model of the human eye.
• To investigate the mechanisms behind acute microgravity-induced ocular changes.
• To understand the relationship between IOP, ICP, and episcleral venous pressure (EVP) in microgravity.

Main Methods:

• A finite element numerical model of the human eye, optic nerve, and surrounding tissues was constructed.
• The model incorporated fluid dynamics and tissue properties, accounting for hydrostatic gradients and compressive forces.
• Model validation was performed using clinical data from intravitreal injections and dark room provocation tests.

Main Results:

• Eliminating hydrostatic pressure in microgravity increased EVP and ICP at the lamina cribrosa.
• Model predictions for IOP closely matched experimental data from supine and parabolic flight conditions.
• Loss of hydrostatic gradients significantly increased IOP, primarily due to effects on ICP and EVP.

Conclusions:

• The initial rise in IOP during short-duration microgravity is likely caused by the loss of hydrostatic gradients.
• Altered EVP and ICP play crucial roles in microgravity-induced IOP elevation.
• The validated numerical model provides a tool for understanding ocular changes in spaceflight.