point TOPIC: Silicone Hydrogels and Lens Comfort

The Role of Silicone Hydrogel Lenses in Patient Comfort

BY ROBIN L. CHALMERS, OD, FAAO

For the past 15 years, I have worked on teams chasing an understanding of suboptimal ocular comfort, both with and without contact lenses. I have studied dry eye disease and contact lens-related dryness. Symptoms from many thousands of contact lens wearers have shown me that contact lens-related dryness causes patients to say they have "dry eye," and is an important factor in discontinuation of contact lens wear (Doughty, 1997; Chalmers, 2002).

In particular, worsening late-day dryness and discomfort describe the struggle that hydrogel contact lens wearers face as they proceed through their long, active days. So, let's focus on evidence from symptoms of late-day dryness and discomfort as primary performance measures for patient comfort with silicone hydrogel lenses.

Refitting Studies Show Promise

One study has shown that when hydrogel contact lens wearers are refit with silicone hydrogel lenses, the result is a clinically significant reduction in reports of late-day dryness and discomfort (Chalmers, 2005). In fact, one recent analysis showed that symptoms reported by silicone hydrogel lens wearers were more similar to those reported by non-lens wearers than to those reported by hydrogel lens wearers (Chalmers, 2008). A caution is that patients enrolled in such studies may show some bias in their responses, usually in the direction of improvement. This is known as the Hawthorne effect, in which merely participating in a study imparts some perceived benefit to the subject. This effect could account for some of the difference in symptoms before and after refitting, so I have recently pursued other means to approach this question that were not tainted by the Hawthorne effect.

Silicone Hydrogel Wearers Report Better Comfort

In a recent survey of 882 young adult contact lens wearers who were using habitual contact lenses and not actively participating in a clinical trial, approximately twice as many hydrogel lens wearers reported extreme end-of-day dryness and discomfort compared to the patients who were wearing silicone hydrogel lenses at the time (Chalmers, 2009).

In this large group of patients who were using many different lens types, there was also evidence that the silicone hydrogel lens wearers had been offered these newer materials in response to earlier contact lens-related dryness. Twenty percent of the silicone hydrogel wearers reported a previous diagnosis of dry eye, compared to 12 percent of the hydrogel lens wearers. This difference could suggest that practitioners are indeed using silicone hydrogel contact lenses in practice to help patients who experience dryness and discomfort.

In addition, silicone hydrogel lenses seem to be more resilient than hydrogel contact lenses to various environmental stressors experienced during normal contact lens wear. Patients wear their contact lenses in so many settings: in dry places, while napping, to a smoky pub, and while driving with the air conditioner running. In one study, 80 percent of silicone hydrogel wearers were comfortable in these settings compared to only 40 percent of hydrogel lens wearers (Young, 2007). Doubling the number of patients who have good comfort in stressful environments is one good reason to consider refitting hydrogel wearers with silicone hydrogels.

Silicone hydrogel patients also reported more hours of comfortable lens wear (Riley, 2006). Ask your patients about dryness and discomfort late in the day and consider whether silicone hydrogel lens materials can help make them more successful contact lens wearers. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #161.

Dr. Chalmers is an independent clinical trial consultant and an adjunct professor at Indiana University School of Optometry. Since 1985, she has conducted clinical trials studying contact lens complications, dry eye, and the measurement of ocular surface symptoms. She is a consultant or advisor to Alcon, CIBA, and Vistakon and an advisor to Bausch & Lomb.

counterpoint

Are Silicone Hydrogel Lenses Really More Comfortable?

BY NOEL A. BRENNAN, MSCOPTOM, PHD, FAAO

Two misconceptions are currently making the rounds in the contact lens field. The first is that higher Dk/t is associated with better comfort and, thus, that silicone hydrogel lenses are inherently more comfortable than are hydrogels. The second is that there is no effective difference in comfort within the silicone hydrogel lens group.

Factors for Lens Comfort

Contact lens comfort is driven by a number of factors including such things as lens design, material modulus, and surface properties. Important surface features include lubricity (or slipperiness), wetting, and deposition pattern. Individual patient differences such as tear quality, lid anatomy and tightness, and general sensitivity also impact comfort. These factors overwhelm any influence that oxygen might have.

Moreover, there is limited credible scientific evidence relating oxygen to comfort. Studies claiming better comfort with higher Dk/t have lacked the basics of evidence-based rigor such as randomization, masking, and control. Consequently, a range of different biases remain unchecked. In reality, a low-Dk/t lens, such as PMMA or a thick HEMA lens, might provide greater comfort than would a high-Dk/t lens, albeit through the undesirable mechanism of corneal anesthesia.

Measuring Comfort

Comfort measurement is subject to the inherent vagaries of inter-and intra-subject variation. Further, traditional analytic techniques are insensitive to important changes. In a large ongoing investigation at Brennan Consultants (Melbourne, Australia), we have performed more than 800 one-month daily wear trials with 12 different contact lens brands. The comfort measurement protocol is standard across trials and carefully implemented; expectations of heightened performance with new products are mitigated, and data is analyzed with a sophisticated statistical paradigm. We have indeed found that a silicone hydrogel is the most comfortable lens. But several hydrogels rate as more comfortable than many popular silicone hydrogel lenses — and we've found differences among the silicone hydrogels, especially for "end-of-day" comfort. We have not yet retested some of the silicone hydrogel brands that ranked least comfortable but have since undergone enhancements to improve their comfort.

The ability to measure comfort differences does not automatically translate to clinical importance. We have therefore separately demonstrated that our comfort measures correlate with lens wear success. For every one-point drop on our hundred-point comfort scale, discontinuations increase by about one percent. These research findings are corroborated by global practitioner experiences. Most agree that silicone hydrogels do not necessarily improve comfort and actually can reduce it in some patients.

We have recently heard of comfort differences associated with corneal staining using different care regimens. While there are certainly individual reactions to care systems, I don't believe that these comfort differences have been fully deciphered. For example, I have seen advanced staining with quaternary ammonium solutions that remains asymptomatic, so the staining-discomfort link is not absolute.

What Course to Take?

Initial comfort is a good indicator of future comfort. If a patient is not especially comfortable with one contact lens type, and you've taken measures to settle the lens, it may be more expedient to try a different lens to improve longer-term comfort. Silicone hydrogel lenses are generally preferred, but you must choose a lens with the right combination of properties to optimize individual patient comfort. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #161.

Dr. Brennan is director of Brennan Consultants Pty Ltd and an adjunct professor at Queensland University of Technology. He has received research funding from Alcon, Allergan, AMO, Bausch & Lomb, CIBA Vision, Clearlab, CooperVision, Igel, and Johnson & Johnson.