A new three-dimensional model to describe human corneal oxygenation during contact lenses wear.

PURPOSE

This three-dimensional study investigated how different contact lens materials affect oxygen levels in the cornea. Specifically, it measured oxygen tension, flux and consumption in the epithelium, stroma and endothelium when exposed to various contact lenses. The goal was to understand how oxygen distribution within the cornea changes based on the oxygen tension at the cornea-tear interface, which is influenced by the lens's oxygen transmissibility.

METHODS

To achieve this goal, a finite element analysis model was used that accounted for the axisymmetric properties of the cornea. A parametric analysis was conducted to examine how lens power and refractive index impacted oxygen distribution. This involved testing various contact lens materials with different powers (±3 and ±6D) and refractive indices.

RESULTS

This three-dimensional model provides new insights into the flux and concentration profiles of oxygen across the epithelium, stroma and endothelium for contact lenses having different optical powers. The key findings show that contact lens thickness and refractive index, which are related to the power, significantly impact oxygen concentration within the cornea. Notably, reduced corneal oxygen consumption occurs primarily at the epithelium, where oxygen tension decreases under both open-eye and closed-eye conditions. This decrease depends on the oxygen permeability of the contact lens being worn and its power.

CONCLUSIONS

The cornea can sustain normal metabolic processes (aerobic metabolism) if the oxygen levels at the cornea-tear film interface are within approximately 60-100 mmHg. This holds true for all of the contact lenses tested here under open-eye conditions. However, when the eyes are closed, the cornea is unable to maintain normal metabolic processes, leading to a shift towards anaerobic metabolism. Prolonged exposure to these conditions can cause corneal oedema (swelling) due to an inadequate oxygen supply.