Plasma protein influx in contact lens wear

Abstract

Purpose: Tear osmolarity and the concentrations of ocular electrolytes in the eye are known to influence corneal health. Similarly, corneal cells are known to be sensitive to changes in electrolyte balance. Ion transport through contact lenses can influence electrolyte equilibration between preand post-lens tear film. Until now no suitable technique has been identified to quantify these effects. This study utilised ion chromatography to examine multiple ion transport through lenses and the measurement of ex-vivo tear samples. Methods:AmodifiedDionex ion chromatographenabled simultaneous measurement of Na+/K+/Ca2+ and Mg2+ concentrations in both single (5 l) tear samples and lens/membrane permeation studies. In addition to commercial contact lenses, conventional HEMA membranes (40% water) and acrylamide-based corneal model hydrogel membranes (ca 90% water) were mounted in purpose-designed permeability cells and the transport of mixed electrolytes (e.g. 0.25M NaCl, KCl and CaCl2) measured. Results: In baseline studies, the relative ratio of the main tear cations measured in healthy tear film samples was found to be Na+:K+:Ca2+:Mg2+ =140:11:1.2:1. This accord with the observation that the range of K+ concentrations in tears (ca 15–30mM) is high and Ca2+ and Mg2+ concentrations (ca 0.4–0.8 and 0.5–1.1mM) is low, relative to serum. The relative permeability coefficients of lenses and membranes were consistent (i.e. NaCl <KCl » CaCl2) ranging between 141.2×10−7: 148.2×10−7: 98.2×10−7 cm2/s (±5% for 90% acrylamide based hydrogel) and 2.8×10−7:3.2×10−7:0.7×10−7 cm2/s (±5% for 40% HEMA hydrogel). Conclusions: Ion chromatography enables tear electrolytes to be accurately monitored in 5 l samples. This, coupled with tear envelope sampling, provides a means of correlating clinical signs and symptoms with post-lens electrolyte concentrations and the ion permeability coefficients of individual lenses. Anisa Mahomed completed an MEng in Chemical Engineering and then obtained her PhD from the Biomaterials Research Group at Aston University. Her thesis discussed the aspects of the fabrication of novel hydrogels for dermal and ocular applications. She is currently a postdoctoral researcher and her interests include investigating factors that affect the uptake, release and transport of various species from hydrogels and developing analytical techniques to enable the understanding of clinical adverse events related to the use multipurpose solutions.