Limitations of in vitro contact lens dehydration/rehydration data in predicting on-eye dehydration.
OBJECTIVE
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.


CONCLUSIONS
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.
McConville
P
P
School of Physics and Cornea and Contact Lens Research Unit, University of New South Wales, Sydney, Australia.
Pope
J M
JM
Huff
J W
JW
D001767:Blinking / Q000502:physiology*; D003263:Contact Lenses, Hydrophilic; D003890:Desiccation; D066298:In Vitro Techniques; D008962:Models, Theoretical; D009799:Ocular Physiological Phenomena; D011237:Predictive Value of Tests; D013666:Tears / Q000502:physiology; D013696:Temperature