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 during acute microgravity exposure are not fully understood.
• While central venous pressure and intracranial pressure (ICP) decrease in weightlessness, IOP paradoxically increases.
• Existing physiological understanding does not fully explain the observed IOP elevation in microgravity.

Purpose of the Study:

• To investigate the mechanisms behind acute microgravity-induced ocular changes.
• To develop and validate a physiologically relevant numerical model of the human eye.
• To predict how microgravity affects intraocular pressure (IOP) by analyzing ocular fluid dynamics and pressures.

Main Methods:

• A finite element numerical model of the human globe, optic nerve, and surrounding tissues was constructed.
• The model incorporated four fluids and twelve tissue types, using properties from existing literature.
• Model validation was performed using clinical data from intravitreal injections and dark room provocation tests.

Main Results:

• Elimination of hydrostatic pressures in microgravity increased episcleral venous pressure (EVP) and ICP at the lamina cribrosa.
• Model predictions for IOP closely matched experimental data from supine and parabolic flight conditions (within 0.7 mmHg and 0.3 mmHg, respectively).
• Loss of hydrostatic gradients significantly increased IOP, primarily due to effects on ICP (0.55 mmHg) and EVP (2.75 mmHg).

Conclusions:

• The initial elevation in IOP during short-duration microgravity is likely caused by the loss of hydrostatic gradients.
• This loss impacts episcleral venous pressure (EVP) and intracranial pressure (ICP), leading to increased IOP.
• The validated numerical model provides a tool for understanding acute microgravity-induced ocular changes.