contact lens materials
Silicone vs. Traditional Hydrogels: ARVO Highlights
BY LORETTA B. SZCZOTKA-FLYNN, OD, MS, FAAO

At the May 2005 Research in Vision and Ophthalmology (ARVO) meeting, researchers shared work that aims at determining whether the risks of microbial keratitis (MK), infiltrative keratitis and contact lens papillary conjunctivitis (CLPC) have changed with silicone hydrogel lenses compared to traditional hydrogel extended wear lenses. Below is a review.

Microbial Keratitis

A study in Sydney, Australia, by Edwards, Keay and colleagues sought to establish risk factors for and the relative risk of MK for different contact lens types. Compared to daily disposable lens wear, the relative risk was approximately 25 times higher with both traditional hydrogel and silicone hydrogel extended wear. Behaviors associated with a higher risk of MK included occasional overnight use of daily wear lenses, not storing lens cases dry, showering in lenses, smoking and inappropriate treatment of lenses while swimming. Additionally, males had a higher risk with 1.6 times greater odds of MK compared to females.

Over a 12-month survey, Professor Efron and colleagues from Manchester, UK, determined the incidence and morbidity of keratitis among wearers of current generation contact lenses. They distinguished between severe keratitis (MK) and non-severe keratitis. Between lens types, the incidence of severe keratitis was 96.4 cases per 10,000 wearers for traditional hydrogel extended wear and only 19.8 cases per 10,000 wearers for silicone hydrogel extended wear. They concluded that silicone hydrogel contact lenses carry a five times lower risk of severe keratitis for extended wear compared with hydrogel contact lenses.

Infiltrates

Chalmers et al presented some one-year data on 6,245 Night & Day (CIBA Vision) continuous wear patients among 131 practices in the United States and in Canada who intended to use a 30-night continuous wearing schedule of lotrafilcon. The researchers reviewed all events of painful, red eyes for the presence of a corneal infiltrate.

Of the reported events, they've confirmed 167 (2.7 percent) corneal infiltrates of varying severity in 158 wearers (2.5 percent). They conclude that these lenses continue to show a promising safety profile as the infiltrate event rate in this post-approval evaluation was similar to that reported in the FDA pre-market approval study.

CLPC

Skotnitsky et al in Sydney, Australia, described the incidence of CLPC in subjects wearing low-Dk and silicone hydrogel contact lenses for extended wear. The incidence of CLPC in low-Dk lens wearers was 3.9 per 100 eye years and in silicone hydrogel wearers was 5.2 per 100 eye years. In the silicone hydrogel group, most of the events were "local" as opposed to generalized CLPC, and at least 60 percent of eyes had a recurrence of CLPC with silicone hydrogel extended wear.

Confirming the findings of the above two studies, our group (L. Szczotka-Flynn and M. Diaz-Insua) presented a meta analysis of the risk of infiltrates and CLPC between silicone hydrogel and traditional hydrogel contact lens wearers. (A meta analysis uses scientific principles to combine all of the relevant research and statistically evaluate the combined results of all the studies in the literature.)

We reviewed 22 studies on 6,343 subjects (12,139 eyes). We found that silicone hydrogels had the same overall risk for corneal infiltrates as traditional hydrogel lenses, but silicone hydrogels carried a greater risk for CLPC.

Dr. Szczotka-Flynn is an associate professor at Case Western Reserve University Dept. of Ophthalmology and is director of the Contact Lens Service at University Hospitals of Cleveland.