(543f) Metabolic Transport from the Limbus Reduces Corneal Edema during Hypoxia | AIChE

(543f) Metabolic Transport from the Limbus Reduces Corneal Edema during Hypoxia

Authors 

Radke, C. - Presenter, University of California-Berkeley
Kim, Y. H., University of California, Berkeley
Oxygen transport from the atmosphere to the cornea plays a significant role in preventing corneal hypoxia and unsafe corneal swelling (i.e., edema). Introduction of a contact lens to the ocular surface can significantly reduce oxygen delivery and may lead to neovascularization or even potential blindness due to excess swelling of the cornea. Clinicians typically measure the swelling of the cornea to assess hypoxia. Corneal swelling is regulated by changes in metabolic concentrations near the endothelium of the cornea due to increased anaerobic metabolism when oxygen tension is low. Reactive production of anaerobic metabolism biproducts, primarily lactate and bicarbonate ions, shifts the chemical potential at the corneal endothelium and results in excess influx of water from the aqueous humor.

We designed a 2D finite element method (FEM) continuum model to assess metabolic reaction kinetics and diffusion of oxygen, carbon dioxide, glucose, bicarbonate, lactate, hydronium, hydroxide, and salt across the cornea, and transport of oxygen and carbon dioxide from the atmosphere through the contact lens and post-lens tear to the cornea. Metabolic support from the aqueous humor and the limbus is correctly accounted for in the 2D calculations. Swelling of the cornea is determined by the change in stromal hydration caused by the change in metabolite concentrations during hypoxia according to the endothelial pump-leak mechanism of Maurice (J. Physiol. 1972) and Kedem-Katchalsky membrane transport. Soft contact lens and scleral lens designs with varying oxygen permeabilities were used to assess various types of lens fitting parameters seen clinically.

Example oxygen tension contours of a typical corneoscleral and contact lens architechture are provided in Figure 1. Solid lines in Figure 2 represent the 2D-predicted swelling profiles for a soft contact and scleral lens with different lens oxygen permeabilities. Maximum swelling occurs at the mid-periphery and zero swelling at the corneal periphery. For comparison, the dashed line in Figure 2 represents predicted swelling with no limbal interaction. Clearly, the limbus dramatically reduces swelling near the corneal periphery. The reason for the dramatic reduction is the supply of bicarbonate and oxygen from the limbus to the cornea and the removal of corneal lactate through the limbus to the sclera. The developed model reveals the importance of limbal supply of metabolites on corneal edema and suggests lower oxygen demand at the periphery than at the center. For the first time, we establish the major role of the limbus in maintaining safe contact-lens wear.