Silicone Hydrogels at the 2004 BCLA Conference

Alisa Sivak, MA, DipEd

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

Overview and Demographics

Noel Brennan (Brennan Consultants, Melbourne, Australia) discussed his experiences prescribing silicone hydrogels for daily and continuous wear. He reported a high level of patient satisfaction, an absence of classic markers of hypoxia though practitioners should watch for signs of papillary conjunctivitis, corneal infiltrative events and hyperopic refractive shifts.

Robin Chalmers (clinical trial consultant, Atlanta, Georgia) and John McNally (CIBA Vision) reported the baseline demographics of 6245 wearers enrolled in a study of patients wearing lotrafilcon A lenses for continuous wear which included middle-age wearers, high refractive errors and long-term wear of contact lenses.

Elizabeth Hill and colleagues (Eurolens Research, Manchester, UK) reported on a study examining changes in attitude to continuous wear and refractive surgery during 12 months of continuous wear of silicone hydrogel or high Dk RGP lenses. The attitudes of silicone hydrogel and RGP lens wearers were moderately positive or very positive, though the scores for RGP lenses dropped initially. Attitude scores for laser refractive surgery remained mildly negative to mildly positive throughout the study.

Randall Sakamoto (International Clinic, Tokyo, Japan) discussed the physiological benefits of high Dk/t materials. He outlined the clinical differences between high Dk RGP and silicone hydrogel lenses and showed that both lens types give good results with continuous wear, though complications occur occasionally.

Clinical Performance and Physiological Effects

Using high Dk silicone hydrogels as an example, Nathan Efron (Eurolens Research, Manchester, UK) and Noel Brennan reviewed and outlined the limitations of using lens oxygen transmissibility as a means of measuring critical oxygen availability for sustaining normal corneal respiration. They also discussed the measurement of corneal oxygen flux as a more accurate methodology.

Fiona Stapleton (Vision CRC, University of NSW, Australia) discussed the results of a study comparing subjects wearing hydrogel lenses or silicone hydrogel lenses on an extended wear basis, and subjects who had never worn lenses. Results indicated that hydrogel lens wearers had the highest degree of epithelial thinning and morphological alterations to the basal epithelial cell layer. The level of epithelial thinning in silicone hydrogel lens wearers was similar to the amount experienced by non-lens wearers.

Adverse events such as contact lens papillary conjunctivitis and CLPU can be induced by immunological and/or pathological reactions resulting from the adsorption of surface deposits by silicone hydrogel lenses. Jacinto Santodomingo-Rubido (Neurosciences Research Institute and Biomaterials Research Unit, Aston University, Birmingham, UK) reported on the clinical and biochemical ocular changes experienced by neophyte silicone hydrogel wearers over an 18-month period, including significant increase in bulbar and palpebral hyperaemia associated with specific protein markers.

Ralph Stone (Alcon Laboratories in Forth Worth, Texas, USA) showed how dynamic contact angles are a useful measurement of contact lens wettability. pHEMA-MAA and silicone hydrogel lenses were exposed to simulated blinking conditions, and a sessile water drop technique with high speed video equipment was then used to measure the contact angle of solution on the lenses. pHEMA lenses showed significant dewetting properties with each cycle, while the wettability of the silicone hydrogel lenses was dependent on the type of surfactant used in the pre-soaking solution. These dewetting characteristics appear to be dependent on the surface chemistry of the lenses.

Bruce Evans (City University, London, UK) discussed how silicone hydrogels have been successful in treating orthoptic anomalies, particularly in juvenile anisometropic patients. They have also been able to improve the best corrected acuity of the amblyopic eye and, for some patients, obtain good steroacuity.

Toric lenses

Using Orbscan measurements, William Reindel and colleagues (Bausch & Lomb) showed that the central and peripheral overnight swelling responses for toric and spherical lenses made from balafilcon A were the same. In addition, there were no statistically significant differences in mean primary gaze orientation or mean rotational recovery between balafilcon A and conventional hydrogel toric lenses.

Shifting from low to high Dk contact lenses

Bill Long and John McNally (CIBA Vision) found that subjects benefited from switching to high Dk silicone hydrogel lenses: conjunctival redness and staining, corneal neovascularization, limbal redness and papillary conjunctivitis all improved. Signs of corneal oedema, corneal infiltrates, epithelial microcysts and mucin balls, clear at dispensing, remained clear throughout the study. Forty-nine percent of subjects reported being able to wear their lenses comfortably for a longer period of time.

Kathy Dumbleton (Centre for Contact Lens Research, University of Waterloo, Canada) discussed a similar study showing that bulbar and limbal hyperemaia decreased significantly when subjects switched to high Dk silicone hydrogel wear and that subjects also reported improvements in end of day redness, dryness and comfort.

Complications, Signs and Symptoms

John McNally and Robin Chalmers reported the interim results of a study relating the development of corneal infiltrates with continuous wear of lotrafilcon A lenses and factors reported by wearers at baseline. The development of corneal infiltrates with continuous wear of silicone hydrogel lenses may be associated with age under 30 years, casual hand washing behaviour and swimming while wearing lenses.

Will Ayliffe and colleagues (Mayday University Hospital, Surrey, UK) described the case of a 26-year old patient with microbial keratitis and Pseudomonas aeruginosa associated with continuous wear of silicone hydrogel lenses. Aggressive and immediate treatment included hourly doses of ofloxacin and gentamicin, and hospitalization. The patient had a loss of visual acuity, increased corneal aberrations, corneal scarring and endothelial cell loss.

Solutions

Kathy Dumbleton compared the clinical performance of a PHMB-based system and a peroxide-based (PX) system in disinfecting two types of silicone hydrogel lenses worn on a daily wear basis. No significant subjective differences were reported. Lens comfort decreased and dryness increased over the day regardless of the lens/care combination. The PX-based system produced no significant corneal staining with either lens type. The PHMB system produced significantly greater corneal staining, particularly with balafilcon lenses.

Christopher Amos (CIBA Vision) compared the performance of a Polyquad multipurpose cleaning and disinfection system (MPS) with a peroxide (PX) based system when used with lotrafilcon A lenses worn on a daily wear basis. The PX-based system provided better overall and end of day comfort and less corneal staining.