contact lens materials

A Look at Silicone Hydrogel Use

BY NEIL PENCE, OD, FAAO

While Midwesterners may be known for being conservative (I prefer "appropriately considered") in their actions, the rate at which silicone hydrogel (SiHy) lenses were implemented into practices was surprisingly rapid. For many years, we have queried practitioners returning to Indiana for summer CE offerings about their lens habits and preferences. The findings from summer 2004 show that SiHy spheres were roughly 25 percent of the lenses fit. In 2005 it was approaching 50 percent, and it surpassed the 50 percent mark by mid-2006. Based on sales, the U.S. spherical lens market passed the 50 percent mark for SiHy use in early 2007.

There continue to be suggestions, however, that SiHy use may be overstated by industry sources. It may be useful to share some findings from this summer's CE participants, most of whom were doctors from Indiana and surrounding Midwestern states. Their practice experience ranged from two years to more than 50.

Surveying Lens of Choice

When asked their soft lens of choice to fit a 24-year-old −3.25D myope, 81 percent named a SiHy lens. Interestingly, if the age was 12, a SiHy was picked 76 percent of the time, with the entire 5 percent difference accounted for by increased daily disposable recommendations. For a patient experiencing symptoms of lens-related dryness, 76 percent state a SiHy as their preferred lens. Of the remaining 24 percent, half were daily disposable lens choices.

When questioned about toric soft lenses, 90 percent listed a SiHy as their lens of choice. While these have been on the market a shorter time than spherical SiHy lenses have, it appears the acceptance of SiHy torics has been very rapid.

Interestingly, while it is common for practitioners to routinely prescribe full sphero-cylindrical correction in spectacles even in the presence of relatively low degrees of astigmatism, this is not always the case for contact lens prescriptions. For example, for a patient with a refractive error of −2.00 −0.75 x180, only 56 percent would start with a toric lens if fitting soft lenses. With the excellent performance of many soft toric lenses, their use for these prescriptions should be higher.

Regarding presbyopes, respondents reported monovision as the clear favorite through 2004. Since then, fitting with monovision or multifocals has been about equal. There was a slight leaning toward monovision this year compared to the past two years. With the recent introduction of several SiHy multifocals, the balance might be expected to change next year.

Several items surveyed concerned GP lenses. Fifty percent report that GP wearers make up 5 percent or less of their lens patients. Twenty-five percent reported that number was either 0 or 1 percent, the assumption being that they do not fit GP lenses or rarely might refit a GP patient. The unfortunate truth is that these are more likely to be younger practitioners, which indicates that fitting GP lenses may become a narrower specialty.

Finally, practitioners were asked if they had ordered a PMMA lens within the past 12 months. Almost 20 percent responded yes. An informal survey of four laboratories in the United States revealed that roughly 1 percent of rigid lens orders are PMMA. The assumption is that the orders are for refits only. A similar survey of European labs found it was about 0.1 percent, which begs the question: do U.S. practitioners fit more PMMA than European practitioners do?

A Rapid Response

While typically not thought of as early adapters, Midwestern practitioners have been relatively quick to recommend SiHy lenses. The higher Dk and improved technology have been embraced for patient benefits. With excellent GP materials available, I wonder when we�ll do the same for all rigid wearers, and eliminate PMMA use? CLS

Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana. He is a consultant or advisor to B&L, CIBA Vision, and Vistakon, and has received research funding from AMO.