SiHy EXTENDED WEAR LENSES
Deciphering the Safety Data of SiHy Contact Lenses
Studies show the excellent safety profile of high-Dk/t SiHy lenses.
Dr. Eiden: The clinical performance of silicone hydrogel (SiHy) contact lenses has been studied more comprehensively than any other vision correction modality, especially for safety and complications. Multiple clinical investigations, including large-scale, FDA-mandated post-market surveillance studies,1–13 have shown that SiHy lenses have an excellent safety profile. These studies have documented potential health benefits, such as decreased corneal edema, reduced corneal acidosis, improved endothelial morphology and lower bacterial adherence.
Let's carefully review the outcomes of these studies and how they impact clinical decision-making.
STUDIES OF SIHY-RELATED MK
Dr. Eiden: Everyone on the panel is obviously comfortable with continuous-wear use of SiHy lenses. However, some practitioners remain cautious about their safety, based on past experiences with extended-wear, low-Dk/t HEMA soft lenses.
I'd like to discuss the safety data. We've all seen the postmarket surveillance studies10 of lotrafilcon-A, published by Schein and colleagues10 in 2005. So how do the Dk/t levels of lenses affect vision loss associated with microbial keratitis (MK)?
Dr. Szczotka-Flynn: The Schein post-marketing surveillance study1 of Night & Day lenses showed the MK rate was about 18 in 10,000, or 1 in 500. Patients have similar risk when they sleep in low-Dk/t HEMA lenses for 7 days or sleep in high-Dk/t SiHy lenses for up to 30 days. Therefore, SiHy lenses worn for longer periods also have the same absolute incidence of MK as low-Dk HEMA lenses worn for shorter periods. Stapleton14 also found a similar rate of SiHy lens-related MK in Australia, and others have shown similar findings.
Dr. Hom: There's some evidence that SiHy extended wear lenses are associated with a lower rate of vision loss compared with low-Dk/t HEMA extended wear lenses. It's also important to note that we can manage MK much more effectively than we did in the past.10
Dr. Eiden: Good point. Do vision loss or severity of keratitis statistics differentiate between low Dk/t HEMA lenses and higher Dk/t SiHys?
Dr. Hom: Morgan15 studied keratitis (Figure 1) and found that extended-wear SiHys were associated with a 5-fold decreased risk of severe keratitis compared with low Dk/t HEMA lenses worn on an extended-wear basis.
Figure 1. In one study, extended-wear silicone hydrogel contact lenses were associated with a fivefold decreased risk in severe keratitis compared with low Dk/t HEMA extended-wear hydrogel lenses.
Dr. Davis: The Schein study10 showed that about 5 in 25,000 patients who continuously wore lotrafilcon-A lenses for 3 to 4 weeks had decreased vision because of MK. Evidence suggests that this amount of vision loss is only half the amount of vision loss associated with low Dk HEMA extended wear lenses.10,16
Dr. Eiden: How has this finding influenced your practice?
Dr. Davis: The Morgan study3 that showed a fivefold decreased risk in severe keratitis demonstrated that patients who want to sleep in lenses should be fit with silicone hydrogels.
Dr. Goldberg: The parents of my younger patients want to know their children's lenses are safe, and many don't want their children sleeping in contact lenses. I tell them these lenses are healthier and the risk of serious complications is low.
LASIK VS. CONTINUOUS WEAR
Dr. Eiden: Patients may be considering LASIK refractive surgery versus continuous contact lens wear. Some LASIK proponents claim the procedure is safer than contact lens wear, but well-designed studies — including a recent ARVO presentation by Stapleton and colleagues17 — refute that claim. What does the research say about the relative safety of LASIK versus contact lens wear?
Dr. Davis: Stapleton17 showed that vision loss from LASIK was equivalent to about 10 years of overnight soft contact lens wear, and about 69 years (a lifetime) of any contact lens wear. Direct comparisons of LASIK to contact lenses are problematic. Any degree of vision loss from LASIK occurs quickly, whereas contact lens-related vision loss happens over time. And LASIK can cause irreversible, disabling glare or severe dryness, from which contact lens wearers typically can find relief.
Dr. Hom: A 2005 study10 by Schein also examined visual acuity loss of 2 lines or more. Although the study didn't evaluate LASIK, the authors mentioned that the incidence of vision loss among LASIK patients was 1 in 100, compared to 1 in 5,000 for patients wearing Night & Day for 30 days continuously. That's a huge difference in risk.
Dr. Eiden: This reminds us of one of our challenges: Always differentiate between significant and insignificant complications. It's inappropriate to group all complications of contact lens wear together versus breaking out visually significant complications.
Dr. Sorrenson: In the real world, you rarely observe severe events. As partial owner of a LASIK center that sees 300 contact lens patients every month, I've never seen a patient lose two lines of visual acuity. LASIK and extended wear are both very safe. You have to carefully explain the risks to patients and take steps to prevent them.
Dr. Szczotka-Flynn: To determine the incident rate of rare complications, you need thousands of patients. LASIK studies have been very well controlled, but they look at straight vision loss, not quality of vision and higher-order aberrations. There's more variability in the contact lens data that comes from the population-based studies.
Finally, because SiHys are a fairly new technology, the rate of problems in a population-based study may be skewed because practitioners often put problem patients in the newest lenses. Keay18 published a study showing that the complication rate of frequent-replacement lenses was high when they first debuted, because practitioners put problem patients in them first.
Dr. Eiden: That's an excellent point.
Dr. Goldberg: I discuss all modalities with my patients, including LASIK, but I stress that SiHy lenses will meet most of their needs. I have the flexibility to make adjustments with contact lenses that I don't have after LASIK.
PRESCRIBING HIGH-DK/T SILICONE HYDROGELS
Dr. Eiden: Dr. Hom, how do you talk to your patients about the benefits and risks of continuous-wear SiHy contact lenses?
Dr. Hom: If they want continuous wear, I tell them I'll only prescribe SiHys, because they're the safest and healthiest for their eyes.
Dr. Eiden: Dr. Goldberg, what about you?
Dr. Goldberg: Many children who have severe vision problems are referred to me, and sometimes SiHys are the modality that ultimately corrects their vision. For example, I had a 5-year-old patient with 4.0D of myopic astigmatism and attention deficit hyperactivity disorder. No way could he handle the daily process of caring for his lenses at home. By putting the child in extended-wear lenses, I safely corrected his vision. I proactively recommend these lenses to patients of all age groups — even elderly patients who have issues with handling their lenses.
Dr. Eiden: Do you ever need to educate your patients about the benefits of high-Dk SiHy lenses vs. older, low-Dk HEMA extended-wear lenses?
Dr. Davis: Yes. I often ask contact lens wearers, "Do you ever want to sleep in your lenses?" and they say, "Oh, no! When I wake up, my eyes feel terrible!" I discuss how traditional HEMA lenses deliver less oxygen to the eyes than newer SiHy lenses. Typically, people don't wake up with that same awful feeling as though the lenses are stuck to their eyes. Also, if patients have demonstrated a myopic shift over time due to the low oxygen transmission of low Dk/t HEMA lenses, I discuss how hyper Dk/t SiHy lenses can lessen the chance of a myopic shift. Patients are thrilled about that.
Dr. Eiden: It sounds as if your clinical experiences with today's hyperoxygen permeable contact lens materials make you comfortable fitting and proactively prescribing continuous-wear contact lenses. How has the introduction of SiHy lenses helped shape your professional opinions?
Dr. Hom: I prescribe SiHys for continuous wear without hesitation. I don't believe there's a better modality or better material to use for continuous wear. It's a no-brainer for me.
Dr. Eiden: Dr. Davis, how about you?
Dr. Davis: I feel comfortable offering these lenses to my patients who want continuous wear — and most of them do. I look at every case individually and always prescribe continuous wear with caution. It feels really good to offer the latest and greatest technology, especially when it provides clear, comfortable vision, convenience and safety.
CONTINUOUS WEAR SIHY LENSES NO LONGER A RISK
Dr. Eiden: Clinical decision-making often is based on a risk-to-benefit ratio. Continuous wear contact lenses for overnight use provide multiple lifestyle advantages for our patients. Historically, eyecare professionals believed continuous wear lenses were associated with a high risk for developing significant complications. Nevertheless, patients continued to wear these lenses. Those who didn't still desired to do so if a safe alternative became available.
SiHy lenses provide much higher levels of oxygen to the cornea. Although the overall rates of MK haven't been affected by the introduction of SiHy lenses, the severity and risk for vision loss secondary to MK have been potentially reduced. In addition, the relative risk of MK in general, and vision loss associated with MK specifically, must be put into context with other life risks.
In the lotrafilcon-A post market survey study, Schein and colleagues10 wrote: "The absolute risk for continuous wear of SiHy lenses seems reasonable from a public health perspective … ."
It's the responsibility of each contact lens practitioner to use evidence-based medicine when deciding if prescribing continuous wear contact lenses is appropriate for individual patients. Contemporary SiHy lenses allow many patients to experience the benefits of continuous wear with greater safety than ever before. I wish to thank all of you on this panel for participating in this highly informative discussion. CLS
1. Lin MC, Graham AD, Polse KA, McNamara NA, Tieu TG. The effects of onehour wear of high-Dk soft contact lenses on corneal pH and epithelial permeability. CLAO. 2000;26:130–133.
2. Sweeney DF. Clinical performance of silicone hydrogel lenses. In: Sweeney DF. Silicone Hydrogels: the rebirth of continuous wear contact lenses. Oxford: Butterworth Heinemann; 2000:113.
3. Fonn D. High Dk versus approved 7-day extended wear hydrogel lenses: the overnight corneal swelling response. Optom Vis Sci.1997;74:76.
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6. Stapleton F, Kasses S, Boli S, Keay L. Short term wear of high Dk soft contact lenses does not alter corneal epithelial size or viability. Br J Ophthalmol. 2001;85:143–146.
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8. Sweeney DF. Clinical performance of silicone hydrogel lenses. Silicone Hydrogels: The rebirth of continuous wear contact lenses. Oxford: Butterworth Heinemann;2000:137.
9. Morgan PB, Efron N, Hill EA, Raynor MD, Whiting MA, Tullo AB. Incidence of keratitis of varying severity among contact lens wearers. Br J Ophthalmol. 2005;89:430–436.
10. Schein OD, McNally JJ, Katz J, et al. The Incidence of microbial keratitis among wearers of a 30-day silicone hydrogel extended-wear contact lens. Ophthalmology. 2005;112:2172–2179.
11. Chalmers RL. Not all keratitis is created equal: It is the visual outcome that is important. Visit siliconehydrogels.org/editorials/jul_06.asp. July 2006. Last accessed Aug. 11, 2009.
12. Dillehay S, Long B, Barr J, et al. Summary of 3 Year in-practice trial in the US with lotrafilcon A silicone hydrogel soft contact lenses. Optom Vis Sci. 2005;(82) E-abstract 050080.
13. Dillehay S, Long B, Barr J, et al. Annual incidence reports for adverse events in a 36-month trial with a silicone hydrogel soft contact lens. Optom Vis Sci. 2005;(82) E-abstract 050077.
14. Stapleton F, Keay L, Edwards K, et al. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology. 2008;115:1655–1662.
15. Morgan PB, Efon N, Hill EA, Raynor MD, Whiting MA, Tullo AB. Incidence of keratitis of varying severity among contact lens wearers. Br J Ophthalmol. 2005:89:430–436.
16. Cheng KH, Leung SL, Hoekman HW, et al. Incidence of contact-lens associated microbial keratitis and its related morbidity. Lancet. 1999;354:181–185.
17. Stapleton F, Naduvilath T, Wu Y, et al. The risk of vision loss in contact lens wear and following LASIK. Poster presented at The Association for Research in Vision and Ophthalmology, May 3–7, 2009, Fort Lauderdale, Fla.
18. Keay L, Radford C, Dart JK, Edwards K, Stapleton F. Perspective on 15 years of research: reduced risk of microbial keratitis with frequent-replacement contact lenses. Eye Contact Lens. 2007;33:167–168.
S. Barry Eiden, OD, FAAO, (moderator) is president and medical director of North Suburban Vision Consultants, Ltd., a private group practice specializing in primary eye care, complex contact lens management, treatment of eye diseases and refractive surgery. He's cofounder and president of EyeVis Eye and Vision Research Institute. He's an assistant clinical professor at the University of Illinois at Chicago Medical Center in the department of ophthalmology, Cornea and Contact Lens Service, and an adjunct faculty member of the Illinois, Salus, and UMSL Colleges of Optometry. Dr. Eiden has served as a consultant to Alcon, CIBA Vision and Synergeyes. He has received research funding from Alcon, Coopervision, EyeVis, Hydrogel and Synergeyes. He has been a member of advisory panels for CIBA Vision, Coopervision, Special Eyes and Synergeyes.
Jennifer E. Davis, OD, practices in Waynesboro, Va., and has been in private practice for 8 years. She was selected as Virginia's Young Optometrist of the Year in 2007. She's an adjunct assistant clinical professor at Pacific University College of Optometry and a visiting assistant professor of ophthalmology at the University of Virginia. Dr. Davis is a member of the Alcon speaker's alliance and the CIBA Vision speaker's bureau.
Fred Goldberg, OD, FAAO, is the founder of McLean Eyecare Center, a group practice in McLean, Va. He's served as a clinical faculty member at the Pennsylvania College of Optometry. He's lectured on pediatric contact practice and written articles on practice record keeping. He's the immediate past president of the Virginia Optometric Association and is the 2009 Virginia Optometrist of the Year. Dr. Goldberg has consulted for CIBA Vision.
Milton M. Hom, OD, FAAO (DipCL), practices in Azuza, Calif. He's a Diplomate in Cornea and Contact Lenses and has written more than 150 articles in various publications. He serves on several editorial boards and has published more than 25 abstracts and peer-reviewed studies. He's the author of Mosby's Ocular Drug Consult and Manual of Contact Lens Prescribing and Fitting, Third Edition. Dr. Hom has received research funding from Alcon, Allergan, AMO, Bausch & Lomb, CIBA Vision and Inspire.
Laurie Sorrenson, OD, FAAO, is part of a group private practice in Austin, Texas, and is 4th year Practice Management Coursemaster at the University of Houston College of Optometry. She's spoken extensively on therapeutic management of LASIK, glaucoma, dry eyes, keratoconus, topography, contact lenses, anterior segment pathology and oral medications. Dr. Sorrenson has been an advisor to CIBA Vision and Crystal Practice Management.
Loretta Szczotka-Flynn, OD, MS, FAAO (DipCL), is associate professor at Case Western Reserve University, Department of Ophthalmology & Visual Sciences, and director of the Contact Lens Service at the University Hospitals Case Medical Center in Cleveland. She's a Diplomate in the Cornea and Contact Lens Section of the American Academy of Optometry and Diplomate award chair for the section. She has received research funding from Alcon, CIBA Vision, Coopervision and Vistakon.