Silicone Hydrogel Lenses: Not Just for Continuous Wear

Silicone hydrogel (SH) contact lenses are an amazing technological breakthrough. I can remember when I worked for Dow Corning Corporation, a silicone based chemical company, in the early 1980s and we were merely hopeful that such a lens would be possible. Now, with three different brands of silicone hydrogel lenses available worldwide and more under development, it appears that they will most likely become the mainstay lens of the first part of this century.

Already, silicone hydrogel lenses have been surprisingly well accepted for up to 30 days of continuous wear in both Australia and England, and there is debate about how well accepted they have become for continuous wear in the United States. According to industry sources, about 70 percent of SH wearers wear them for extended or continuous wear (Table 1).

Table 1. Distribution of Wearing Schedules for SH Contact Lenses

Whether more people are wearing contact lenses for extended or continuous wear or not, silicone hydrogel lenses have certainly made contact lens wear safer for the people who wear them. Those patients that choose to wear their lenses on an extended or continuous wear basis benefit from a near absence of hypoxia related complications from contact lens wear. ^1-4Certainly, physical lens trauma and inflammatory and infectious conditions still occur, ^5-9 but our own use of these lenses is based on the belief that they are the healthiest reusable lenses on the market.

Many US practitioners have been reluctant to proactively prescribe silicone hydrogel lenses for up to 30 days of continuous wear. Nevertheless, these lenses are likely to become the lens of choice in the near future for nearly all patients with history of eye redness and/or dryness with soft contact lens wear, whether they are worn on a daily, extended or continuous wear basis. Both our experience and data, like that of others, ^{2, 10} indicate that these lenses reduce dry eye complaints and improve comfort with long term wear, particularly in relation to late day comfort. Silicone hydrogel lenses are also a healthy alternative in light of the fact that a very high proportion of patients who wear soft contact lenses sleep with their lenses in place at least occasionally.

We recently managed a severe soft contact lens related corneal abrasion with a brand of silicone hydrogel lens approved for therapeutic use by the FDA, though bandage lenses are typically not indicated for contact lens related abrasions. We also prefer to use silicone hydrogel lenses as the soft lens component of piggy-back lens fitting for complicated cases of irregular cornea treatment.

Despite the health benefits and convenience of these lenses, practitioners need to remain vigilant when prescribing them for patients. We have observed, as have others, that patients with clinically significant dry eye (without contact lens wear), or who are exposed to smoky environments, or who insist on swimming and then sleeping with their lenses in place, are at high risk for complications with continuous wear ^9,11-13. It is also important to note that ocular surface alteration and corneal staining may occur when silicone hydrogel lenses worn on a daily wear basis interact with some solutions ¹⁴.

Improved spherical silicone hydrogel lenses will be available in 2004, with specialty lenses to follow in the near future. Although their cost will increase, and despite the fact that some eye care practitioners will continue to resist prescribing them for overnight wear, there is no question that we will see considerable growth in the proportion of patients wearing them in the future.

1. Covey M, Sweeney DF, Terry RL, Sankaridurg PR, Holden BA. Hypoxic effects on the anterior eye of high Dk soft contact lens wearers are negligible. Optom Vis Sci 2001;78:95-9.

2. Brennan N, Chantal Coles M, Comstock T, Levy B. A 1-year prospective clinical trial of Balafilcon A (PureVision) silicone-hydrogel contact lenses used on a 30-day continuous wear schedule. Ophthalmol 2002;109:1172-7.

3. Keay L, Sweeney DF, Jalbert I, Skotnitsky C, Holden BA. Microcyst response to high Dk/t silicone hydrogel contact lenses. Optom Vis Sci 2000;77:582-5.

4. Nilsson S. Seven-day extended wear and 30-day continuous wear of high oxygen transmissibility soft silicone hydrogel contact lenses: a randomized 1-year study of 504 patients. CLAO J 2001;27:125-36.

5. Dumbleton K. Noninflammatory silicone hydrogel contact lens complications. Eye & Contact Lens 2003;29:S186-S9.

6. Lim L, Loughnan M, Sullivan L. Microbial keratitis associated with wear of silicone hydrogel contact lenses. Br J Ophthalmol 2002;86:355-7.

7. Skotnitsky C, Jalbert I, O'Hare N, Sweeney D, Holden B. Case reports of three atypical infiltrative keratitis events with high DK soft contact lens wear. Cornea 2002;21:318-24.

8. Sweeney D, Stern J, Naduvilath T, Holden B. Inflammatory adverse event rates over 3 years with silicone hydrogel lenses.[ARVO Abstract]. In: The Association for Research in Vision and Ophthalmology; 2002; Florida, USA: http://www.arvo.org 2002.

9. Edwards K, Brian G, Stretton S, Stapleton F, Willcox M, Sankaridurg P, Sweeney D, Holden B. Microbial keratitis and silicone hydrogels. Contact Lens Spectrum 2004;January.

10. Malet F, Pagot R, Peyre C, Subirana X, Lejeune S, George-Vicariot MN, Bleshoy H, Long B. Subjective experience with high-oxygen and low-oxygen permeable soft contact lenses in France. Eye & Contact Lens: Science & Clinical Practice. 2003;29(1):55-9.

11. McNally JJ, Chalmers RL, McKenney CD, Robirds S. Risk factors for corneal infiltrative events with 30-night continuous wear of silicone hydrogel lenses. Eye Contact Lens. 2003 Jan; 29(1 Suppl): S153-6.

12. Lee,K.Y. Lim,L. Pseudomonas keratitis associated with continuous wear silicone-hydrogel soft contact lens: a case report. Eye Contact Lens 2003; 29(4):255-257.

13. Sweeney D, Fonn D. Silicone Hydrogels: An Update. http://www.siliconehydrogels.org Editorial February 2003.

14. Jones,L. MacDougall,N. Sorbara,L.G. Asymptomatic corneal staining associated with the use of balafilcon silicone-hydrogel contact lenses disinfected with a polyaminopropyl biguanide-preserved care regimen. Optom Vis Sci; 2002;79(12):753-761.