Alisa Sivak, MA, DipEd

Alisa assists the Centre for Contact Lens Research by writing and editing publications, reports, grant applications, and educational communications.

Part Two (September 2005)

This is the first half of a synopsis of silicone hydrogel-related posters and presentations at the BCLA conference in Brighton, UK. There were a total of 27 silicone hydrogel-related posters and presentations covering all silicone hydrogels currently available (see Table 1). This half of the synopsis describes presentations relating to clinical performance, oxygen flux, microbial keratitis and the performance of lens care products.

Overview

Brighton, UK

Lyndon Jones (CCLR) revisited the industry’s dream of producing a lens able to provide vision and comfort without placing hypoxic stress on the eye. He reviewed the development of new contact lens materials and care products over the last 20 years, asking, “Are silicone hydrogel contact lenses the technological breakthrough we have been waiting for?” Overall, he concluded, though silicone hydrogels represent a significant step in the right direction, the development of better surface treatments enhancing wettability and antibacterial surfaces aiming to reduce inflammatory events will result in even better materials.

A session led by Brien Holden emphasized the benefits of wearing silicone hydrogel lenses, including a reduction in chronic contact lens related problems: hypoxia, ocular redness and end of day dryness. Patients with higher-than-average needs for oxygen, and those with higher prescriptions, require lenses with the highest oxygen transmissibility – not just at the centre, but across the entire lens. Comfort, bacterial contamination and microbial keratitis are issues that still need to be addressed with regards to these lenses.

Clinical performance and subjective preference

Devi Priya Janakirman and colleagues (CIBA Vision) compared the overall performance of silicone hydrogel (lotrafilcon B) toric lenses with low-Dk ocufilcon D toric lenses in a three-month clinical trial. The subjective response to the lotrafilcon B lenses was better than or equal to the oculfilcon D lenses, in addition to providing good centration and rotational stability and a statistically significant improvement in limbal and bulbar redness.

Hans Roth (ophthalmologist, Switzerland) and colleagues reported on the performance of lotrafilcon B, a lens intended for daily, flexible or 6-night extended wear. A statistically significant majority of the silicone hydrogel wearers refit with this lens preferred it to their habitual lenses, particularly in relation to end-of-day comfort. A number of participants appreciated the option of occasional overnight wear with their daily wear lenses, and 70% reported that they occasionally fall asleep while wearing their habitual lenses.

Robin Chalmers (clinical trial consultant, U.S.A.) and colleagues reported the results of a post-market evaluation of patients wearing lotrafilcon A on a continuous wear basis. At the one-year mark, 80% of the 5,903 registered in the evaluation were still wearing the study lenses. Among other questions, wearers were asked whether they had experienced an episode of painful, red eyes causing them to seek eye care, and all events were reviewed for the presence of a corneal infiltrate. The evaluation found one hundred and eighty (2.9%) corneal infiltrates of varying severity in 164 wearers. Seventy-nine percent reported that they had been wearing the lenses for at least 21 nights in a row; 9.3% wore the lenses for 1-2 weeks at a time; 7.6% wore the lenses for 1-6 nights, and 3.2% wore the lenses for daily wear only.

Franck Earith and Rolland Pagot (private practitioners, France) conducted a one-month, multi-site evaluation of comfort and clinical performance with galyfilcon A lenses. Their results revealed high comfort ratings and a high level of overall acceptance. Paul Chamberlain and colleagues (OTG Research and Consultancy) also found that in vivo wettability, comfort and overall acceptance were higher with galyfilcon lenses compared to that of a conventional hydrogel lens.

Ken Gellatly (private practitioner, Canada) presented the results of a multi-site Canadian study evaluating patient satisfaction with extended wear of senofilcon A lenses. These lenses were graded significantly higher than lotrafilcon A lenses in terms of comfort and overall performance.

Clare O’Donnell and colleagues (University of Manchester) compared the performance of two silicone hydrogel lenses worn as bandage lenses after refractive surgery. Eighteen patients wore a balafilcon A lens in one eye and a lotrafilcon A lens in the other eye for a three-day period after surgery. Results indicated similar clinical performance: subjective evaluations of comfort were similar for both lenses; there was less deposition on the balafilcon A lens; by evaluation day the epithelium had healed completely in 89% of balafilcon-wearing eyes and 82% of lotrafilcon-wearing eyes.

Nikki Iravani and colleagues (Coopervision) compared the clinical performance of a silicone hydrogel lens (galyfilcon A) with a biomimetic lens (omafilcon A) for daily wear. Results indicated that clinical performance was similar for both lenses, and improved in comparison with conventional hydrogels. Subjects reported an overall preference for the biomimetic lenses.

Oxygen Flux

Ian Cameron and colleagues (Eurolens Research) illustrated the oxygen performance of conventional and silicone hydrogel lenses by measuring lens thickness at 36 discrete points across the diameter of a variety of lens types in a range of back vertex powers, and calculating Dk/t and oxygen flux values for each point. All silicone hydrogel lenses worn for daily wear provided over 95% ‘flux’ (oxygen reaching an eye with no contact lens in place). The same lenses worn for extended wear provided 90% flux or greater, as did hydrogels worn for daily wear. Extended wear hydrogels provided 60% flux or more. Some lower-Dk hydrogels provided less than 20% flux with extended wear.

Microbial Keratitis

An Australian team presented the results of a 12-month, prospective study of contact lens-related microbial keratitis – the first of its kind since the advent of silicone hydrogels and daily disposables. Fiona Stapleton (Vision CRC, UNSW) and colleagues found that the annual incidence of contact lens-related MK was 4.8 per 10,000 wearers. With daily wear of silicone hydrogels, it was 4.5; and with extended wear of silicone hydrogels it was 19.3. These figures are in comparison to an incidence of 0.9 per 10,000 with daily disposables, 3.1 with daily wear, and 11.7 with extended wear of soft contact lenses. Loss of vision occurred more frequently with extended wear of soft contact lenses compared with extended wear of silicone hydrogels. MK with silicone hydrogel extended wear appeared to be associated with a longer duration of continuous use. Extended wear of any contact lens is associated with a higher risk of MK compared to daily wear. Katie Edwards and colleagues (Vision CRC, UNSW) found that out of 700 contact lens-wearers, 151 cases of MK were reported within the first six months of the study. The relative risk of MK with daily wear of a silicone hydrogel was 1.4 times the risk with daily disposables – the same as daily wear of hydrogels. Extended wear of silicone hydrogels posed 25.5 times the risk compared to extended wear of soft lenses, which posed 24.6 times the risk. RGP lenses posed 0.2 times the risk. These results support the observation that extended wear of lenses, whether hydrogel or silicone hydrogel, pose a higher risk of MK.

Silicone hydrogels and care products

Ann Wright (CIBA Vision) presented the results of a study using flow cytometry to evaluate the viability of SV-40 transformed human corneal epithelial cells exposed to high oxygen permeable silicone hydrogel contact lenses and a variety of lens care products. The analysis demonstrated that Clear Care and Aquify MPS are much less cytotoxic to human epithelial cells than Opti-free Express.

Karen Sentell and colleagues (CIBA Vision) measured preservative uptake and release from PHMB-containing lens care products by three types of silicone hydrogel lenses. Lotrafilcon B took up the least amount of PHMB, followed by lotrafilcon A and galyfilcon A, while balafilcon A took up the highest amounts. Uptake of PHMB from ReNu Multiplus was greater (with measurable release into saline) than from Aquify (little to no measurable release into saline after soaking) for all materials. Preservative uptake by silicone hydrogel lenses appears to depend not only on the level of preservative used in the lens care product but also on the matrix of the overall solution formulation. These results indicate that not all preserved lens care solutions are equally suitable for silicone hydrogel lenses, and different brands of silicone hydrogels appear to have different propensities for preservative uptake from lens care solutions.

Part Two of the BCLA synopsis will cover friction, fit and material properties; optics; adsorption of elements from the tear film; and comfort and wettability.