Alisa Sivak, MA, DipEd

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

The following is part two of a synopsis of silicone hydrogels at the 2008 meeting of the BCLA:
Using the sessile drop method of measuring contact angle, Walter Nash and colleagues (CIBA Vision) found that surface-treated lotrafilcon B lenses direct from a packaging solution containing a comfort additive exhibited lower advancing contact angles than lenses made from  lotrafilcon A and B, balafilcon A, comfilcon A, galyfilcon A and senofilcon A, also direct from packaging solution. (123)  Michael Reach and colleagues (Eurolens Research, UK) reported that senofilcon A, lotrafilcon A and a hydrogel lens soaked in packaging solution had lower sessile contact angles, but that there were significant differences between the lenses when contact angles were measured using the captive bubble technique.  This group also noted that measurements made with the sessile drop method were less repeatable than those taken with the captive bubble method.  Intra-lens repeatability also differed between lens types.  Senofilcon A demonstrated the greatest variability in contact angles. 
According to Yu-Chin Lai and colleagues (Bausch and Lomb), high molecular weight materials used for “super highly oxygen permeable” silicone hydrogel lenses are surprisingly oxygen permeable – higher than expected based on their water content.  (127)

Research performed by Jennifer Zuba and Paul Jeatran (Bausch and Lomb) found that balafilcon A lenses exhibited consistent negative spherical aberration across sphere powers, while lotrafilcon A and B, galyfilcon A and comfilcon A lenses exhibited a linearly increasing trend that under-corrected for average spherical aberration at low minus powers. (127)

Huangang Chen (Alcon) and colleagues (University of Buffalo) reported that a lubricant eye drop containing polyethylene glycol (PEG) had a lower coefficient of friction than lubricant eye drops containing other ingredients. (119)

Kurt Moody (Vistakon) and colleagues (McMaster University, Canada) reported that senofilcon A lenses, which incorporate PVP, have lower levels of surface friction than other silicone hydrogel lenses tested – comparable to friction levels found with conventional hydrogels. (130)
Noel Brennan and colleagues (Brennan Consultants, Australia) reported a high correlation between discontinuation and comfort scored on a visual analog scale. (133)

Giancarlo Montani and colleagues (State University of Lecce, Italy) proposed using quantitative image analysis to evaluate corneal staining type and extent, classifying micropunctate, macropunctate, coalescent macropunctate and patch staining according to corneal area covered.  Their research indicates that this procedure is useful, particularly in evaluating small areas of corneal staining. (113)

Melanie George and colleagues (CIBA Vision) designed an assay to evaluate solution performance in the presence of lenses and lens cases (compared to conventional tests, which examine solutions independently).  Lenses were inoculated with microorganisms and stored in cases, to simulate contamination by handling.  Results indicated that solutions worked best with silicone hydrogels prepared in this manner, and had lower efficacy when used with Group I and Group IV lenses.  There was also lower clinical contamination with a PHMB-based solution compared to a polyquad-based solution. (115)

Sally Buck and colleagues (Alcon Laboratories) evaluated two contact lens disinfecting solutions for their efficacy against Acanthamoeba cysts and trophozoites, using methodology based on a modified version of the FDA, ANSI and ISO Regimen test for bacteria and fungi.  Results showed that two different polyquad-based formulations effectively eliminated traces of Acanthamoeba from silicone hydrogel lenses.

Graeme Young (Visioncare Research Ltd., UK) and colleagues (Centre for Contact Lens Research, Canada) clinically evaluated subjects who were using either a PHMB or a polyquad-based care system on a long-term basis.  Results indicated that the PHMB-based system was associated with significantly more grittiness/scratchiness, palpebral roughness, hyperaemaia, corneal and conjunctival staining, as well as higher levels of tear film deposits.  Front surface lens wettability was significantly better with the polyquad-based system. (117)