THE OCULAR SURFACE / JANUARY 2006, VOL. 4, NO. 1 / www.theocularsurface.com 24 Silicone Hydrogel Contact Lenses and the Ocular Surface FIONA STAPLETON, PHD, MCOPTOM, DCLP FAAO, 1,2, 3 SERINA STRETTON, PHD, 1,2 ERIC PAPAS, PHD, MCOPTOM, DCLP, 1,2,3 CHERYL SKOTNITSKY, BSC,OD, 1, 3 DEBORAH F. SWEENEY, BOPTOM, PHD, FAAO 1,2,3 Accepted for publication November 2005 From the 1 Vision Cooperative Research Centre, Sydney, Australia, 2 Insti- tute for Eye Research, Sydney, Australia, and 3 School of Optometry and Vision Science, University of New South Wales, Kensington, Australia All authors are supported in part by the Australian Federal Government through the Cooperative Research Centre Scheme. The authors have no commercial interest in any concept or product dis- cussed in this article. Single copy reprint requests should be sent to: Deborah F. Sweeney (ad- dress below) Corresponding author: Deborah F. Sweeney, Vision Cooperative Research Centre, PO Box 6327, UNSW Sydney, NSW, 1466, Australia. Tel: +61 2 9385 7408. Fax: +61 2 9385 7401. Email: d.sweeney@visioncrc.org Abbreviations are printed in boldface where they first appear with their definitions. ©2006 Ethis Communications, Inc. The Ocular Surface ISSN: 1542- 0124. Stapleton F, Stretton S, Papas E, et al. Silicone hydrogel con- tact lenses and the ocular surface. 2006;4(1):24–43. Clinical Science S GARY N. FOULKS, MD, SECTION EDITOR KEY WORDS biomaterials, contact lens, corneal homeosta- sis, corneal vascularization, giant papillary conjunctivitis, limbal hyperemia, palpebral conjunctiva, papillary conjunctivi- tis, silicone hydrogel, tear film I. INTRODUCTION ilicone hydrogel contact lenses represent the most important advance in the contact lens industry since development of the first soft hydrogel lenses in the early 1970s. The high oxygen permeability of this new class of silicon-based soft lens materials has provided a distinctive platform upon which new developments and designs are conceived. Until silicone hydrogel lenses be- came available, soft lens wearers, particularly those who wore lenses overnight, were subject to the effects of con- tact lens-induced hypoxia on corneal physiology and the potential consequences of compromised corneal integrity and function. The Göteborg study, published in 1985, was one of the first studies of the physiological effects of soft contact lens wear on the cornea. 1 This study compared 27 eyes that had used long-term extended wear (5 years) hydrogel lenses with their non-lens-wearing fellow eyes. The lens- wearing eyes showed significantly thinner corneal epithe- lium and lower oxygen uptake rates, greater numbers of corneal epithelial microcysts, thinner corneal stroma, sig- nificant levels of daytime edema, and a greater degree of corneal endothelial polymegethism than the fellow eyes. It has also been shown that long-term wearers of hydrogel lenses have greater amounts of limbal hyperemia than non- lens wearers, and may have greater encroachment of limbal vessels into the cornea. 2 Although the changes to the stroma and endothelium remained, many of the changes to the epithelium seen in Göteborg study were reversed over 1 month after cessa- tion of lens wear; in particular, epithelial thickness and oxygen consumption steadily recovered to non-lens wear- ing levels, as did the numbers of microcysts. 1 This study confirmed that chronic lens-induced hypoxia is the under- lying cause of the physiological changes seen during long- term contact lens wear and provided the major impetus to ABSTRACT For 30 years, contact lens research focused on the need for highly oxygen-permeable (Dk) soft lens materials. High Dk silicone hydrogel contact lenses, made available in 1999, met this need. The purpose of this review is to examine how silicone hydrogel lens wear affects the ocular surfaces and to highlight areas in which further research is needed to improve biocompatibility. Silicone hydrogel lenses have elimi- nated lens-induced hypoxia for the majority of wearers and have a less pronounced effect on corneal homeostasis compared to other lens types; however, mechanical interaction with ocular tissue and the effects on tear film structure and physiology are similar to that found with soft lens wear in general. Although the ocular health benefits of silicone hydrogel lenses have in- creased the length of time lenses can be worn overnight, the risk of infection is similar to that found with other soft lens types, and overnight wear remains a higher risk factor for infec- tion than daily wear, regardless of lens material. Future con- tact lens research will focus on gaining a better understanding of the way in which contact lenses interact with the corneal surface, upper eyelid, and the tear film, and the lens-related factors contributing to infection and inflammatory responses.