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A. J. Bron, J. M. Tiffany, E. Gaffney, N. Yokoi; Predicted Phenotypes of Dry Eye - Proposed Consequences of its Natural History. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3639.
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Tear hyperosmolarity plays a key role in the mechanism of dry eye. We have explored the influence of tear evaporation, lacrimal flux and blink rate on tear osmolarity, and the impact of compensatory and decompensatory events.
Mathematical modelling and a review of the literature.
A model for the mass and solute balance of the tears predicts a higher osmolarity in the tear film than the meniscus, with the differential rising with increased meniscus osmolarity. This implies that in dry eye, meniscus samples may underestimate potential damage to the ocular surface. The model also suggests that increases in blink rate may play a limited role in compensating for a rise in tear osmolarity in aqueous-deficient dry eye (ADDE) but that an increase in lacrimal flux, together with an increase in blink rate, may delay the development of hyperosmolarity in evaporative dry eye (EDE). Various reports indicate that aqueous tear deficiency may reduce spreading of the tear film lipid layer and considerations of the lacrimal functional unit suggest that loss of corneal sensitivity in dry eye could reduce the compensatory lacrimal secretion. It is hypothesized that such events, occurring late in the natural history of dry eye, alter the clinical phenotype so that, with progression, hybrid forms of dry eye evolve, with ADDE taking on features of EDE and vice versa.
These predictions are compatible with our current modelling and have diagnostic and therapeutic implications.
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