Alisa Sivak, MA, DipEd

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

Part 1

Staining

The staining that occurs with certain combinations of silicone hydrogel materials and multipurpose solutions continues to be explored worldwide. Gary Andrasko (private practitioner) and Kelly Ryen reported that excessive corneal staining was more likely to occur with PHMB-based solutions than with hydrogel peroxide or polyquad.  Surface-treated silicone hydrogel materials tended to induce the greatest staining area.  Comfort consistently decreased when average staining area was greater than 30%, and reached a peak early in the lens wearing day.  Christine Sindt and colleagues (University of Iowa) reported that staining associated with balafilcon A lenses was more clinically significant and covered a wider area when subjects used a PHMB-based solution.  Subjects using this solution also reported a significant drop in comfort.  Motozumi Itoi (private practitioner) evaluated corneal staining resulting from different combinations of silicone hydrogel lenses and solutions marketed in Japan.  Results show moderate to high staining when these lenses were combined with PHMB-based solutions after two hours of wear, compared to minimal staining with other solutions. Finally, Loretta Szczotka-Flynn (Case Western Reserve University) and colleagues assessed the reliability and accuracy of grading photographically documented corneal staining.  The level of agreement was moderate between readers and moderate to substantial within reader.  The ability to accurately grade corneal staining when combining two masked readings is high. 

Others explored mechanical staining caused by the lens itself:  Gary Andrasko and colleagues found that senofilcon A lenses, which have a low modulus demonstrated significantly lower mechanical corneal staining than lotrafilcon B.  Milton Horn (private practitioner), however, reported that higher modulus materials do not have more impact on the conjunctiva.  He found that lotrafilcon B had significantly lower amounts of conjunctival staining compared to galyfilcon A, which has half the modulus. 

Adverse events

Pseudomonas aeruginosa (PA) continues to be the leading causative agent in contact lens keratitis.  Danielle Robertson and H. Dwight Cavanagh (UT Southwestern Medical Centre) conducted a 12-month study aimed at determining the effects of long-term daily wear compared to overnight wear of three hyper-oxygen permeable silicone hydrogel contact lenses.  Results indicate that the risk for keratitis with daily and extended wear of lenses is similar over one year:  Extended wear was associated with an initial decrease in central epithelial thickness that recovered over the one-year study period, while daily wear had no significant effect on central epithelial thickness.  All lens wear decreased epithelial surface cell desquamation, with recovery over the year.  There was no significant difference in PA binding.

Carol Lakkis and Shubha Lakkola reported no significant differences between worn and unworn comfilcon A lenses with respect to PA adherence.  There was greater adherence with unworn lotrafilcon A lenses compared to unworn comfilcon A lenses, but no significant differences between these lens types after wear.  Adherence of the cytotoxic strain was significantly greater with worn balafilcon A lenses compared to worn comfilcon A and lotrafilcon A lenses.  Adherence of the invasive strain was significantly lower after wear of balafilcon A, but the cytotoxic strain showed significantly greater adherence after wear.  Overall, the invasive strain showed significantly greater adherence to all unworn and worn lens types compared to the cytotoxic strain. 

Bill Long and colleagues (CIBA Vision) used a scale of 0 to 4 to grade biomicroscopy signs and corneal adverse events in subjects wearing lotrafilcon A lenses for continuous wear.  At 12 and 24 months, correlations were found for corneal infiltrates and corneal edema.  Correlations were found for neovascularization at 12 months, and correlations were found for conjunctival staining and infiltrates at 24 months.

Comfort and wettability

Padmapriya Ramamoorthy and colleagues (Ohio State University) reported that contact lenses in FDA groups 2 and 4 were more likely to be associated with contact lens dry eye than lenses in group 1.  Contact lens dry eye was also strongly associated with recent lens refit and the frequent use of rewetting drops.

William Reindel and colleagues (Baush & Lomb) found that balafilcon A and galyfilcon A lenses have similar tear dynamics whether soaked in a polyquad- or PHMB-based solution.  Milton Horn (private practitioner) reported that a PHMB-based lens care solution was associated with greater overall comfort, end-of-day comfort and overall cleanliness in addition to demonstrating a trend towards a slightly longer pre-lens tear thinning time, compared to a polyquad-based solution.

Noel Brennan and colleagues (Brennan Consultants) reported a high correlation between initial comfort and one-month dryness and end-of-day comfort.  One-month, end-of-day comfort scores associated with balafilcon A, etafilcon, hioxyfilcon, lotrafilcon B, omafilcon and polymacon were significantly lower than ratings for average comfort.  There was considerable overlap between the comfort scores generated for silicone hydrogel lenses and conventional hydrogels, indicating that factors other than oxygen transmissibility have a predominant effect on dryness and end-of-day comfort symptoms during contact lens wear.

Friction between the contact lens surface and the lid may be an important factor predicting lens comfort.  Using lateral force microscopy measurements on lenses submerged in an aqueous environment, Heather Sheardown and colleagues found that senofilcon lenses had levels of friction lower than other silicone hydrogel materials and comparable to those observed on conventional hydrogel materials. 

Lakshman Subbaraman and Lyndon Jones (CCLR) determined that comfilcon A lenses are associated with low advancing sessile-drop water contact angles, particularly after soaking in a polyquad-based lens care solution.   The angles were lower than those reported for other silicone hydrogel materials; the solution seemed to have altered the surface properties of the lens material.

Sebastian Marx and Wolfgang Sickenberger looked at existing lens wearers custom fit with sifilcon A lenses.  Results showed that comfort improved significantly, as did limbal redness. 

Deposits

The Centre for Contact Lens Research (University of Waterloo) reported a number of studies aimed at exploring the deposition of protein on silicone hydrogel lenses.  Adrienne Boone and colleagues confirmed that all silicone hydrogel lens materials deposit low levels of protein, and that the amount and percentage of denatured lysozyme varies depending on surface treatment:  Balafilcon A accumulates significantly more total protein and lysozyme than other lenses.  This material also had the lowest percentage of denatured lysozyme compared to lotrafilcon A, which had the highest percentage of denatured lysozyme.  Lakshman Subbaraman, Lyndon Jones and colleagues looked at five silicone hydrogel lens materials to determine the quantity of total protein, total lysozyme and the conformational state of lysozyme deposits.  Although both surface-modified and non-surface-modified silicone hydrogel lenses accumulate low levels of protein, balafilcon A accumulates the most total protein and total lysozyme per lens, while there was no difference between the other lenses investigated.  In particular, the quantity of protein and conformational state of lysozyme deposited on sifilcon A lenses, which are worn on a three-month replacement schedule, is similar to that found on other surface-coated silicone hydrogel lenses after one month of wear.  Finally, this group determined that the reduction in the activity of lysozyme recovered from various lens materials is time-dependant, with the rate varying between materials.

Lens-wearing experiences

Barry S. Elden and Robert Davis compared five toric lenses:  three silicone hydrogel and two hydrogel.  Although most measures of lens performance were relatively equivalent between the five lens designs, balafilcon and galyfilcon A were rated the least comfortable, galyfilcon was rated significantly more difficult to handle, and the Biomedic Toric was ranked easiest to handle. 

Langis Michaud and Etty Bitton (Universite de Montreal) shared their findings in tracking student contact lens experiences.  Within a six-month period (2006-2007) and 1996 recorded visits in contact lens clinics, silicone hydrogel lenses represented 34.8% of dispensed lenses.  Soft conventional lenses represented less than 1% of all fits. 

Bill Long and colleagues profiled contact lens experience among patients in eye care offices.  Adapted contact lens wearers showed improved clinical signs (conjunctival redness, limbal redness, neovascularization) subjective signs (dryness) and comfort when they changed to lotrafilcon A for daily wear.