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 of the BCLA synopsis will focus on adverse events and complications, and physiology and optics in addition corporate posters.  To view part one of this synopsis, please click here.

Adverse events and complications

Mark Wilcox and colleagues (Institute for Eye Research) discussed significant factors associated with a higher risk of inflammatory events subjects wearing silicone hydrogel lenses on an EW basis for a six-month trial.  They included higher levels of microbial lens contamination, corneal vascularisation, less lens movement and “non-ideal” or outdoor environments.  Factors associated with mechanical events included higher levels of palpebral roughness, corneal staining and less wetting of lens surface.

Oxygen should not be the only consideration when fitting lenses, according to Tom Løfstrøm (Synoptik):  mechanical complications associated with the fit of silicone hydrogel lenses should also be kept in mind. In particular, excessive conjunctival folds caused by tight lenses are not necessarily visible with staining.  Further, a number of refittings are often needed with extended wear lenses, and complications can occur as a result.

Arthur Back (CooperVision) and colleagues (Brennan Consultants, Clinical Vision Research Australia, Centre for Contact Lens Research) reported that over a 12- to 24-month period, the overall rates of infiltrative keratitis with comfilcon A lenses were 6.1% compared to 5.8% for lotrafilcon and 21.3% for balafilcon lenses.  The overall rate for SEALs was 0% for comfilcon, 1.7% for lotrafilcon and 7.1% for balafilcon.

The effects of various lens-solution combinations were compared by Christopher Amos (CIBA Vision).  Results showed lower levels of corneal staining, conjunctival staining and palpebral redness with a peroxide cleaning system and significantly higher mean scores for cleanliness and clarity of vision.

Physiology and optics

Epithelial barrier data collected by Jerry Paugh et al. (Southern California College of Optometry) revealed statistically significant alterations in epithelial permeability when  (i) balafilcon A lenses were used with a PHMB-based solution compared to lotrafilcon B paired with polyquaternium-1-based solution and (ii) when lotrafilcon B lenses were paired with a PHMB-based solution compared to a lotrafilcon B - polyquaternium-1 combination.  There were no statistically significant alterations in epithelial permeability when balafilcon A lenses were paired with a PHMB-based solution compared to the lotrafilcon B - PHMB combination.

Heather Connor and colleagues (Brennan Consultants) used impression cytology to study patterns of conjunctival change during daily wear of silicone hydrogel lenses (balafilcon  A, lotrafilcon B, senofilcon A and hydrogel lenses).  Results showed a wide pattern of responses between individuals, which appears to be unrelated to lens type.

Fabrizio Zeri (Instituto De Amicis Via Galvni) compared IOP measures with lotrafilcon A lenses to those of a hydrogel lens.  Results showed that the measurements were similar regardless of which type of lens was being worn in the eye, indicating that lens modulus does not affect these measurements. 

Noel Brennan (Brennan Consultants), Nathan Efron (Queensland University of Technology) and Philip Morgan (Eurolens Research) confirmed that maximising contact lens Dk/t is clinically valid, particularly in relation to the threat of vascularisation, and all silicone hydrogel lenses appear to provide enough oxygen to the eye. The higher modulus associated with higher Dk materials, however, may be associated with discomfort, palpebral conjunctival papillary changes, refractive error changes, SEALs, mucin balls and epithelial thinning.
 
Chantal Coles and colleagues (Brennan Consultants) assessed the effect of oxygen transmissibility on limbal redness following overnight wear of silicone hydrogel contact lens materials. Galyfilcon A had the highest mean change in limbal redness compared to lotrafilcon B, senofilcon A and no lens. 

William Reindel and colleagues (Bausch & Lomb) evaluated changes in spherical aberration and high and low contrast visual acuity in an aspheric balafilcon lens and a spherical galyfilcon lens among subjects with large pupils.  Aberrometer measurements with the balafilcon lenses demonstrated a reduction in positive spherical aberrations across the power range.  Reduction in positive aberrations with the other lenses varied by power:  with low powers had less reduction in positive aberrations.  Management of aberrations with the use of aspheric contact lenses can improve visual acuity among patients with large pupils. 

Craig Woods and colleagues (CCLR) compared the power profile of five different silicone hydrogel lenses available on the market and found a large variation in spherical aberration, which may be the reason for reported variations in vision.  Of the ten lenses measured, four were over-powered compared to the labelled value for the nominal vertex power. 

According to Brien Holden (Institute for Eye Research), contact lenses should have a Dk/t level that provides all corneas with the same level of oxygen received without lens wear. By eliminating hypoxic conditions during lens wear, and thus establishing “normoxia”, the cornea is better conditioned to enable a rapid healing response when compromise occurs. 

Corporate posters

R. Cedrone and colleagues (Alcon) reported that subjects wearing galyfilcon A lenses and using a multipurpose solution preserved with POLYQUAD® and ALDOX® reported better and longer lens comfort.  This regimen was also associated with less corneal staining than a PHMB-based solution used in conjunction with lotrafilcon A lenses. Chris Amos and colleagues (CIBA Vision) found that subjects wearing four different silicone hydrogel materials rated a CIBAVision peroxide-based multipurpose solution higher than other MPS solutions tested with respect to cleaning, comfort and clarity of vision.  Larbi van Lier and Timothy Giles (CIBA Vision) introduced made-to-order silfilcon A lenses, with spherical powers form +20.ooD to -20.00D, in three diameters and 14 base curves.

Coming soon:  silicone hydrogel synopsis from the 2007 AAO meeting.