Model of ocular surface ion and water transport predicts efficacy of dry eye therapeutics targeting epithelial transport and tear fluid dynamics
The composition and volume of tear fluid lining the ocular surface are governed by the rates of lacrimal gland secretion, tear film evaporation, nasolacrimal drainage, and epithelial ion and water transport. Tear fluid hyperosmolality and reduced volume are key drivers of dry eye disease (DED) pathogenesis. We constructed a mathematical model to compute the composition and volume of tear fluid and epithelial cell compartments, with transport parameters specified for the mouse eye from published data and in vivo measurements of ocular surface potential differences. The model accounted for transcellular and paracellular transport across the epithelia under open-circuit conditions utilizing flux equations for individual transport mechanisms, with mass balance constraints on solute and water content in cytoplasm and tear fluid. Under DED conditions established by reduced lacrimal secretion and increased evaporation, the model predicted the efficacy of currently available DED therapies including punctal plugs, humidification goggles, lacrimal gland stimulation, and artificial tears eye drops. The model also predicted the limited efficacy of anti-absorptive and pro-secretory drugs targeting epithelial ion transporters, and the high efficacy of targeting epithelial water permeability or paracellular ion permeability. The modeling herein provided quantitative predictions to prioritize novel targets for DED and drive the development of new therapies. Author SummaryDry eye disease (DED) affects billions of adults worldwide, but a full picture is lacking of how the tear film becomes abnormally thin and hyperosmolar. The computer model built here links four processes - tear production by the lacrimal gland, tear fluid evaporation, tear drainage through tear ducts, and transport of solutes and water across eye surface epithelial cells - to predict the thickness and composition of the tear film in various conditions. Model parameters were selected using published data and electrical measurements of voltage changes across the ocular surface produced by ion transport. The model predicted that existing therapies, such as punctal plugs, moisture goggles, or stimulating tear production, can substantially increase tear thickness or lower saltiness. The model also predicted limited efficacy of drug therapies in current development that target ion transport, and identified epithelial cell water transport and paracellular ion permeability as novel targets for DED treatment. By making ocular surface transport mechanisms explicit and testable, our work offers a roadmap for development of new therapies that restore a healthy tear film, a major unmet medical need.