[Experimental assessment of mass transfer in the human cornea using cesium ion migration as a model]

The pathogenesis of endothelial corneal dystrophies involves disruption of the natural balance between fluid influx into and efflux from the corneal stroma. Regulation of fluid transport across the endothelial layer in vivo is primarily associated with the activity of sodium-potassium pumps. However, the role of the physicochemical properties of the cornea as a functioning connective tissue should also be taken into account. One possible approach to assessing the efficiency of water transport in the cornea is the measurement of concentration kinetics of alkali cations.

This study aimed to experimentally assess the physical mass transfer of alkali cations in the human cornea, taking into account the effect of intraocular pressure (IOP), using Cs⁺ as a model.

The experiment used seven corneoscleral flaps with a diameter of 15 mm, which were mounted on an original experimental setup designed to assess the rate of fluid penetration into corneal structures and visualize it. The test was performed both in the absence of hydrostatic IOP simulation and under a pressure of 20 mm Hg with different exposure times. The distribution of cesium across the corneal cross-section was evaluated using scanning electron microscopy with energy-dispersive analysis.

Three stromal zones with different patterns of cation accumulation and transport were identified. It was also established that when alkali cations originated from the aqueous humor, the transverse concentration profile depended on the presence of IOP. Using cesium as a model, it was shown that in the absence of simulated IOP, this alkali cation was distributed evenly from the endothelium to the epithelium, whereas under a pressure of 20 mm Hg its maximum concentration was observed in the mid-stromal zone (180-360 µm).

The original experimental setup and the proposed methodology for studying physical mass transfer in the human cornea demonstrated that, under additional pressure close to intraocular pressure, the stroma represents a heterogeneous medium for penetrating high-atomic-weight alkali cations. This specific feature of corneal osmotic permeability may be used in the future for pharmacokinetic modeling or in other fundamental and applied studies.