contact lens case reports

Silicone-Hydrogel Contact Lenses: Making the Grade

BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FCLSA
September 1999

T.W. is a 32-year-old male with an 8-year history of soft contact lens wear. For the past 3 years, he has been wearing 58% water planned frequent replacement lenses with an intermittent overnight wearing schedule consisting of 2 to 3 nights per week.

T.W. has always reported good comfort and has been compliant with his weekly lens disposal regimen. Historically, he has been physiologically tolerant to intermittent overnight wear and has remained relatively free of adverse responses.

He was switched to Bausch & Lomb's new PureVision contact lens and reported a rather dramatic improvement in comfort (Fig. 1). This surprising improvement has been reported by a significant number of patients who try the PureVision lens and is most likely related to its unique characteristics.

The Chosen Lens

The PureVision lens is one of an entire family of new materials specifically designed to address the demanding physical and physiological requirements of extended wear. It consists of a 36% water content, silicone-hydrogel material with a reported Dk/t of 110. In comparison, traditional hydrogel extended wear lenses generally have a Dk/t of approximately 10 to 30. PureVision's surfaces are molecularly modified to transform the hydrophobic silicone surface into a hydrophilic surface. The surface modification is not a coating, but rather an intrinsic part of the lens.

Recently, our patients have shown a renewed interest in extended wear contact lenses. To date, with this new modality, our only complication has been the periodic appearance of "mucin balls" beneath the periphery of the lens (Fig. 2).

Mucin Balls

Mucin balls appear to be a relatively benign phenomena unique to silicone-hydrogel contact lenses. The particles are reported to be caused by the rolling of tear film components into tiny, discrete balls. The particles result in focal depressions in the epithelium, which can be easily detected with fluorescein (Fig. 3).

Extended wear is a modality desired by a significant number of patients. However, its history has been marred with complications due to the poor physiology and biocompatibility of traditional hydrogel materials. The new generation of silicone-hydrogel contact lenses has addressed many of these problems, and the future of the modality looks significantly more encouraging. 

Patrick Caroline is an associate professor of optometry at Pacific University and an assistant professor of ophthalmology at the Oregon Health Sciences University.

Mark André is director of contact lens services at the Oregon Health Sciences University.