Alisa Sivak, MA, DipEd

Alisa is Communications Coordinator at the Centre for Contact Lens Research, University of Waterloo, Canada

Worldwide fitting trends:

Jason Nichols (The Ohio State University, USA) and Philip Morgan (Eurolens Research, The University of Manchester, UK) provided an overview of the 2009 contact lens market in the USA.  Results of an annual survey indicate that silicone hydrogel lenses account for 54% of fits in the United States. Soft toric lenses account for 22% of fits, 30% of which are silicone hydrogel toric lenses.  In the United States, silicone hydrogels are the most commonly prescribed material for new soft fits, compared to worldwide trends indicating that most patients are still wearing conventional soft lenses (49%) for daily wear, instead of silicone hydrogels (18%).  Silicone hydrogel daily wear accounts for 22% of fits in the UK, 15% in Japan, 23% in the Netherlands, 8% in Hong Kong, and 36% of fits in Australia.

Corneal inflammatory events:

Fiona Stapleton (Institute for Eye Research, Australia) reported that silicone hydrogel lenses have higher rates of infiltrates compared to hydrogel lenses, though the understanding of this difference is complicated by the fact that silicone hydrogels can be worn for longer extended wear schedules.  The risk of infiltrates appears to be higher but less severe in the initial period of continuous wear.  Solution-induced corneal staining may also play a role in the development of infiltrates. 

Corneal staining

The issue of solution-induced corneal staining with certain lens-solution combinations was also touched on by Lyndon Jones (Centre for Contact Lens Research, University of Waterloo, Canada), in a discussion of the challenges presented by silicone hydrogel lenses in the development of care systems:  increased hydrophobicity and lipid deposits, increased levels of denatured lysozyme deposits, and asymptomatic solution-induced staining (sometimes with subtle inflammation).  These factors may make it necessary to focus on the development of solutions formulated specifically for silicone hydrogel lenses. 

Comfort:

Robin Chalmers (USA) and colleagues (Visioncare Research Ltd, UK; Vistakon, Johnson & Johnson Vision Care, USA) reported the results of a questionnaire gathering responses from 699 hydrogel and 183 silicone hydrogel lens wearers.  Those respondents wearing hydrogel lenses struggled more with contact lens wear.  With increasing age, hydrogel lens wearers reported increased dry eye, discomfort related to adverse (dry, smoky) environments, overall discomfort, discomfort after napping or sleeping, and were more likely to consider discontinuing lens wear.  The proportion of silicone hydrogel lens wearers considering discontinuation of lens wear remained steady for all ages. 
Paul Chamberlain and colleagues (Eurolens Research, The University of Manchester, UK) investigated ocular comfort and physiological response in a group of neophytes wearing  narafilcon A (daily disposable) lenses compared to an age- and sex-matched spectacle-wearing population.  Overall results indicated that comfort of the lens-wearers was similar to those not wearing lenses, with no decrease in comfort over the wearing day.  In neophytes, lens comfort improved over the first month of wear, confirming an adaptation effect.  There was minimal impact on ocular physiology.

Conjunctival staining:

According to David Meadows and colleagues (Alcon Research, USA), contact lens-induced conjunctival staining with etafilcon A lens wear may be the result of changes in lens parameters, which can occur over one week of wear. One study conducted by this group found that a change in lens material or base curve decreased contact lens-induced conjunctival staining. A second study measured base curves of senofilcon A lenses following one or two weeks of wear with a polyquad-based or peroxide solution. With both solutions, the base curves of silicone hydrogel lenses steepened after one week of wear, returning to baseline within a few hours of lens removal.  Base curve changes and recovery are influenced by temperature. The third study confirmed that both base curve and corneal curvature change following one week’s wear of senofilcon A with use of polyquad-based, PHMB-based and peroxide solution. 

Replacement frequency:

Daniel Tilia and colleagues (The University of New South Wales, Australia) evaluated which lens replacement schedule results in higher non-compliance.  Following 800 participants for three months of bilateral lens wear, with a total of 24 lens-solution combinations, this group found that compliance was always worse with a two-week replacement schedule compared to a monthly schedule. 
Kathy Dumbleton and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) analysed 1475 surveys relating to patient demographics, lens type, lens-wearing patterns, eye care professionals’ instructions for replacement frequency and patients’ actual replacement frequency.  Practitioners’ recommended replacement frequencies were consistent with manufacturers’ recommendations more frequently with daily disposable and one-month replacement lenses than with lenses designed to be replaced every two weeks.  Patients were most compliant with recommended replacement frequency when wearing daily disposables, and least compliant when following a two-week replacement schedule.  More than half of respondents reported that they forget which day to replace their lenses. 

Deposits:

Doerte Luensmann and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) used confocal laser scanning microscopy and a radiolabeling technique to investigate the penetration profile of albumin and lysozyme in silicone hydrogel lenses incubated in a protein solution (lysozyme or albumin).  Results showed markedly different protein uptake profiles.  With lenses made from balafilcon A and etafilcon A, lysozyme and albumin were detected throughout the lens.  With lenses made from lotrafilcon A, more protein was detected at the surface.  More lysozyme than albumin penetrated the matrix of senofilcon A lenses, while albumin was detected more at the surface of these lenses.  Etafilcon A lenses contained the most lysozyme, and lotrafilcon B contained the smallest amount.  Albumin levels were highest on senofilcon A lenses and lowest on etafilcon A lenses. 

Lysozyme deposits may not have an antimicrobial effect on contact lenses, according to Lakshman Subbaraman and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada; Institute for Eye Research, Australia). This group found no significant difference between lysozyme-coated and uncoated lenses, whether they were silicone hydrogel or conventional hydrogel.  Further, more bacteria (Gram positive and negative) adhered to uncoated silicone hydrogel materials than to uncoated conventional hydrogel lenses.

Lyndon Jones and colleagues (Centre for Contact Lens Research, University of Waterloo, Canada) reported that etafilcon A lenses disinfected with a polyquad-based MPS (with five-second rinse) collect 36% less total lipid than lenses disinfected with peroxide.  An enhanced no-rub regimen used with balafilcon A lenses exhibited levels of deposition similar to – or better than – the rub regimen.
Charles Powell and colleagues (AMO, USA) used spectroscopy to compare “real-world” cleanliness of lotrafilcon lenses used for one month of daily wear with a PHMB-based “rub” regimen compared to a polyquad-based “no-rub” system.   They found that lenses cleaned with the rub regimen had half the lipids and proteins found on lenses cleaned with the no-rub system.