A quantitative description of equilibrium and homeostatic thickness regulation in the in vivo cornea. I. Normal cornea.

By combining a description of the coupled solute and water flows through the in vivo cornea with a set of appropriate mechanical equilibrium conditions, it is possible to calculate directly the corneal thickness, given the corneal temperature, the state of the aqueous and tears, the swelling pressure-hydration relation of the corneal stroma, and the transport properties of the corneal membranes. Active transport of ions or water by the corneal epithelium or endothelium, or both, are explicitly included. When published parameters are inserted into the formulation, the normal corneal thickness is recovered, and the corneal potential, anteriorly directed water flux, and stromal salt content are in reasonable to quantitative agreement with experiment. The analysis yields a simple physical explanation of the stromal imbibition pressure and the opposing forces which cause the cornea to assume its normal thickness.