Extended wear in perspective.
BACKGROUND
Convenience and safety are major motivating factors in the choice of a mode of correction for refractive errors. Extended wear of contact lenses is associated with greater convenience than daily wear, but questions remain concerning the safety and risks associated with this modality. This paper investigates the hurdles that have rendered extended wear an unfavorable option thus far and seeks to identify strategies to overcome these obstacles.


METHODS
We review the history of extended contact lens wear, focusing on soft extended wear for cosmetic use. Results of incidence and relative risk studies for the major complications are scrutinized. The factors that are associated with increased risk together with mechanisms which have been proposed on based on scientific research are analyzed to derive strategies for preventing adverse reactions in extended wear.


RESULTS
Infectious keratitis associated with extended wear of contact lenses has been identified by the community as a major issue, although the degree of concern may be disproportionate. Current perceptions of the relative risk of extended wear versus daily wear in the context of the risk for nonwearers may be misplaced, and the role of eye closure versus consistency and duration of wear remains open to debate. In the minds of practitioners and patients, other adverse reactions may be of greater significance in rejecting extended wear. Nonetheless, the potential extent of injury from infection demands attention. Studies collectively attest that corneal hypoxia during extended wear is a potential causative mechanism in infectious keratitis, suggesting that the provision of higher oxygen levels to the cornea will reduce morbidity rates from this unwanted complication. However, the issues of stagnation of the post-lens tear film during eye closure, mechanical properties of the lens, and lens movement remain unresolved and may prove to be contributing factors to adverse responses.


CONCLUSIONS
Attention to oxygen permeability and mechanical properties of soft contact lenses should solve the remaining problems with extended wear. Materials currently under development promise to meet at least some of the desired properties and may lead to the long-awaited advent of safe extended wear.
Brennan
N A
NA
Brennan Consultants Pty. Ltd., Medical Centre, Melbourne, Australia.
Coles
M L
ML
D000818:Animals; D003262:Contact Lenses, Extended-Wear / Q000009:adverse effects; D003315:Cornea / Q000502:physiology; D015818:Eye Infections, Bacterial / Q000209:etiology; D006801:Humans; D007634:Keratitis / Q000382:microbiology; D010100:Oxygen / Q000378:metabolism; D012030:Refractive Errors / Q000628:therapy*; D012307:Risk Factors; D012449:Safety
D010100:Oxygen