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DEFINITIONS FOR HYDRATION CHANGES OF HYDROGEL LENSES
Author(s) -
BrennanM Noel A.,
Efron Nathan,
Truong Van Tan,
Watkins Rodney D.
Publication year - 1986
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.1986.tb00725.x
Subject(s) - dehydration , lens (geology) , water content , content (measure theory) , self healing hydrogels , body water , through the lens metering , optics , materials science , chemistry , mathematics , physics , body weight , geology , polymer chemistry , biology , mathematical analysis , biochemistry , geotechnical engineering , endocrinology
— Authors of studies on the hydration characteristics of hydrogel lenses have used a variety of definitions to describe the changes observed with exposure of the lenses to different environments. This has resulted in difficulties in the interpretation of published data. In particular, the single term “percentage dehydration” has been used to denote different mathematical expressions for alterations to the lens composition. A detailed theoretical analysis of hydrogel hydration levels is presented to examine definitions for lens hydration changes, compare results obtained under different definitions and propose appropriate usage for the alternative definitions according to the aspect of lens performance under consideration. The interrelationships between the commonly used definitions of dehydration are shown to be independent of initial lens mass but dependent on initial water content. Typically, higher water content lenses undergo considerably larger mass changes than lower water content lenses, an effect that may be masked if these changes are presented as changes of water content. There are a number of clinical consequences of lens dehydration, the importance of which will vary depending on the initial lens water content. It is therefore essential when comparing different water content lenses on the basis of the extent of dehydration to do so with respect to a specific clinical consequence rather than in general terms.