P McConville1, J M Pope, J W Huff. 1. School of Physics and Cornea and Contact Lens Research Unit, University of New South Wales, Sydney, Australia.
Abstract
PURPOSE: The purpose of this study was to use in vitro dehydration and rehydration data to model the predicted hydration changes that may occur as a soft contact lens loses and gains water on the eye between blinks. METHODS: Using a recent in vitro data set for four lens materials dehydrated and rehydrated in saline, we derived a mathematical model to describe dehydration and rehydration time courses. The model further combined the dehydration and rehydration data iteratively, as a function of blink frequency, and pre-lens break-up time. RESULTS: The model showed that reduced break-up times or decreased blink frequencies significantly affected dehydration rates and steady state dehydration for lenses of a variety of water contents. However, the model did not agree with the commonly accepted clinical belief that high water content lens materials dehydrate more than low water content materials. DISCUSSION: The discrepancy of the model with historical observations may be accounted for by one or more of the following factors, which were not accounted for in the present model: 1) temperature dependent dehydration (as a lens is taken from a room temperature vial and warmed when placed on the eye); 2) the colloid osmotic pressure, ionicity, pH, and chemical potential of tears (compared to saline); and 3) dehydration by other non-evaporative mechanisms.
PURPOSE: The purpose of this study was to use in vitro dehydration and rehydration data to model the predicted hydration changes that may occur as a soft contact lens loses and gains water on the eye between blinks. METHODS: Using a recent in vitro data set for four lens materials dehydrated and rehydrated in saline, we derived a mathematical model to describe dehydration and rehydration time courses. The model further combined the dehydration and rehydration data iteratively, as a function of blink frequency, and pre-lens break-up time. RESULTS: The model showed that reduced break-up times or decreased blink frequencies significantly affected dehydration rates and steady state dehydration for lenses of a variety of water contents. However, the model did not agree with the commonly accepted clinical belief that high water content lens materials dehydrate more than low water content materials. DISCUSSION: The discrepancy of the model with historical observations may be accounted for by one or more of the following factors, which were not accounted for in the present model: 1) temperature dependent dehydration (as a lens is taken from a room temperature vial and warmed when placed on the eye); 2) the colloid osmotic pressure, ionicity, pH, and chemical potential of tears (compared to saline); and 3) dehydration by other non-evaporative mechanisms.
Authors: Nery García-Porta; Laura Rico-del-Viejo; Helena Ferreira-Neves; Sofia C Peixoto-de-Matos; Antonio Queirós; José M González-Méijome Journal: Biomed Res Int Date: 2015-03-31 Impact factor: 3.411