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Parameter stability of soft contact lenses made from different materials

Tranoudis, Ioannis & Efron, Nathan (2004) Parameter stability of soft contact lenses made from different materials. Contact Lens and Anterior Eye, 27(3), pp. 115-131.

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Abstract

The parameters of soft contact lenses may alter during wear. A series of clinical and laboratory experiments were conducted in order to examine the parameter stability of eight soft contact lenses manufactured from different materials. The following materials (and nominal water contents) were used: HEMA/VP 40%, HEMA/VP 55%, HEMA/VP 70%, VP/MMA 55%, VP/MMA 70%, HEMA 40%, HEMA/MAA 55% and HEMA/MAA 70% (HEMA: 2-hydroxy-ethyl methacrylate, VP: vinyl pyrrolidone, MMA: methyl methacrylate, MAA: methacrylic acid). Two lenses from each of the eight soft contact lens groups were used in experiments concerning the parameter stability. Six subjects were fitted with lenses for 1 day. Verification of back optic zone radius, total diameter, back vertex power, centre thickness and water content was undertaken at 20 degrees C. In vitro measurements of water content, oxygen transmissibility, total diameter and back optic zone radius were taken at 35 degrees C before lens fitting and after 6h of lens wear. Distortion, discolouration and lens quality were assessed before and after lens wear. When the temperature was raised from 20 to 35 degrees C, a significant reduction in lens water content for all the lens types was observed, as well as a significant reduction in total lens diameter for the majority of the lens types. Water content, oxygen transmissibility, total diameter and back optic zone radius of all the lens types reduced, following a 6h open eye wearing period. For the majority of the lens types, these changes were found to be statistically significant. Distortion, discolouration and quality of the lenses remained unchanged throughout the study with the exception of the HEMA/MAA 70% lens. Correlating a number of parameters generated in this study, gave the following conclusions. High water content materials exhibit a low relative change in oxygen transmissibility following a 6h wear period. Soft contact lens dehydration leads to a decrease in oxygen transmissibility and total diameter, following a 6h wear period. These results will assist practitioners in predicting the alterations that occur in soft contact lens parameters and oxygen performance as a result of lens wear.

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ID Code: 11046
Item Type: Journal Article
Additional Information: For more information, please refer to the journal's website (see hypertext link) or contact the author.
Keywords: Soft contact lens materials, Water content, Oxygen transmissibility, Total diameter, Back optic zone radius
DOI: 10.1016/j.clae.2004.03.001
ISSN: 1367-0484
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)
Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300) > Optical Technology (111302)
Divisions: Current > Research Centres > Centre for Health Research
Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 2004 Elsevier
Deposited On: 28 Nov 2007
Last Modified: 29 Feb 2012 23:29

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