Corneal Oxygen Distribution With Contact Lens Wear

Abstract

This FEA model reproduced Brennan 8-layer model (BEL model) results at the central cornea. However, BEL model parameters yielded regions of oxygen deficiency in the corneal periphery, even in the open eye with no contact lens. If the BEL model cannot account for oxygenation across the whole cornea, it may be incorrect or incomplete. This assertion calls into question any conclusions from the BEL model regarding the minimum contact lens transmissibility needed to fully oxygenate the eye.

Structural and biochemical aspects of keratan sulphate in the cornea

“…Subtle changes in oxygen concentration at increasing stromal depths may be a factor influencing different keratocyte subpopulations throughout the cornea [85]. Recently, considerable attention has focused on the corneal hypoxia known to be induced by contact lens wear primarily to facilitate the development of new materials with less influence upon corneal homeostasis [86,87].…”

Oxygen Diffusion and Edema With Modern Scleral Rigid Gas Permeable Contact Lenses

“…Since oxygen diffusivity and consumption in the human cornea have not been measured directly, Larrea et al, 22 Alvord et al, 23 and Chhabra et al 20 have proposed mathematical models of time-dependent oxygen diffusion that allow estimation of corneal consumption and diffusion. Such models use nonlinear Monod kinetics to describe the local oxygenconsumption rate.…”

The significance of oxygen during contact lens wear

“…One important outcome of 2D modelling activity has been that the distribution of oxygen through the layers of the peripheral cornea is predicted to be substantially different than it is centrally [152]. For the central cornea in the absence of a contact lens, open-eye oxygen concentration falls progressively from atmospheric levels (155 mmHg) at the epithelium to around 20 mmHg at the endothelium.…”

“…In addition they were one dimensional [149][150][151], meaning that although the modelled cornea was multilayered and included an epithelium, stroma and endothelium, its geometry was flat and of uniform thickness. This approach was dictated by the computational power available at that time and improvements in this area over the intervening years have allowed the development of full 2D [152] and quasi-2D [153] models where both the cornea and any overlying contact lens can be given realistic thickness profiles from the centre, right out to the periphery. The quasi-2D approach approximates a full 2D model by combining 1D computations from a series of differing thickness shells.…”