Alisa Sivak, MA, DipEd

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

Silicone hydrogels were well represented at this year’s BCLA conference, including 11 paper sessions and 18 posters.  Part one of this synopsis will cover clinical trials, wettability and protein deposition.  Part two, available next month, will look at presentations relating to adverse events, physiology and optics.

Corneal sensitivity and symptoms

Blanka Golebiowski (Institute for Eye Research) reported a decrease in corneal sensitivity and no change in conjunctival sensitivity in a group of long-term wearers who ceased EW of low-Dk soft lenses, and no changes in sensitivity when they were transferred to high Dk lenses for up to 18 months.  The high Dk/t lenses were found to induce fewer symptoms and less dryness than the low-Dk/t lenses. 

The effect of climate on frequency of ocular surface symptoms was the subject of a study reported by Robin Chalmers (Indiana University) and colleagues (Visioncare Research /Vistakon). Research found no difference between mild and cold climates with respect to frequency of ocular surface symptoms in subjects wearing hydrogel lenses.  Refitting the same subjects with second-generation SH lenses reduced the frequency of all ocular surface symptoms (including discomfort, dryness, redness, foreign-body sensation, stinging and burning and fluctuating vision) for those subjects living in cold climates and reduced dryness, discomfort and eye redness with subjects living in milder climates.

Clinical research

Custom silicone hydrogel lenses offer a good alternative for those who do not fit standard parameters.  Timothy Giles and Rajni Singh (CIBA Vision) noted that the CIBA Vision fitting guide aids practitioners in matching the eccentricity of the eye to the saggital depth of these custom lenses, which is essential for optimal fit.  Wolfgang Sickenberger and Sebastien Marx (JENVIS Research) evaluated fit and visual performance of a made-to-order silicone hydrogel lens (sifilcon A). Current contact lens wearers with spherical ametropia were dispensed lenses within a parameter range of ±20.00D, 11 base curves and three diameters.  After three months’ wear, subjects reported longer comfortable wearing time, improved comfort, and a significant decrease in limbal redness.

In a retrospective study conducted by Nina Mueller (Switzerland) balafilcon A and senofilcon A lenses were significantly less comfortable than galyfilcon A, and galyfilcon A had a significantly higher number of tarsal events than did balafilcon A and lotrafilcon A.  There was no statistical difference between the spherical and toric versions of these lenses, and there was no significant difference between the lenses in terms of bulbar and limbal redness, corneal staining, infection and other corneal anomalies.

Jacinto Santodomingo-Rubido (Menicon) and Maria-José Rubido-Crespo (Euro-Optica) reported the results of a study comparing a prototype silicone hydrogel lens and a galyfilcon A lens with respect to fit and comfort.  In part one of the study, subjects were randomly fit with two different base curves of the prototype lens.  In part two, they wore the base curve they found most comfortable in one eye and a galyfilcon lens in the contralateral eye.  Results indicated that the base curves had similar overall fit (6.3 vs. 8.6) and the overall fit and comfort of the prototype lens were similar to that of the galyfilcon lens.

Distance visual acuity (VA), near VA, reading acuity and stereoacuity are significantly better with monovision, according to Navneet Gupta and colleagues (Aston University), who compared the visual function of balafilcon A multifocal and single vision lenses. There was no significant difference with regard to intermediate VA, reading speed, distance and near contrast sensitivity, and depth of focus range. 

Raquel Gil-Cazorla and colleagues (Vissum) evaluated the clinical performance of balafilcon A and galyfilcon A lenses when worn as bandage lenses in contralateral eyes of LASEK patients, post-surgery.  They found no significant differences apart from tearing, which was greater with the balafilcon lenses 24 hours after the surgery.  Five days after surgery, contact lens debris and comfort were statistically better in the eyes wearing galyfilcon A.  They found no difference in epithelial integrity, though patients reported better comfort with the galyfilcon lenses.

Robert L. Davis (Illinois) shared the results of a multi-centre study comparing the clinical performance of galyfilcon A, lotrafilcon B and oculfilcon disposable toric designs.  Results showed no consistent difference between the three lens designs.

Comfort, wettability and protein deposition
Hydrogel peroxide is an effective lens cleaning regiment for all currently available silicone hydrogel lenses, according to Kathy Dumbleton and colleagues (Centre for Contact Lens Research), who compared its performance when used with galyfilcon A, senofilcon A, balafilcon A, and lotrafilcon A and B.  Although there was variation in deposition and wettability between lens types, they came across no cases of solution sensitivity. 

Fiona Carney and colleagues (CIBA Vision) investigated the extent of protein and lipid adsorption on silicone hydrogel lenses with daily wear.  Participants were randomly assigned to wear lotrafilcon, galyfilcon, senofilcon or balafilcon for two weeks’ daily wear, after which time lipid was extracted.  According to the results, any clinical impact of deposition appeared to be due to lipid rather than protein .

Lyndon Jones and Lakshman Subbaraman (Centre for Contact Lens Research) used an in vitro model to determine the kinetics of lysozyme deposited (through doping) on conventional and silicone hydrogel contact lenses.  With all lenses, there was a gradual decrease in lysozyme activity over a variety of time periods:  over the first three days, with etafilcon; over the first week, with balafilcon and galyfilcon; over the first two weeks, with polymacon and omafilcon; and over 28 days, with lotrafilcon A, lotrafilcon B and senofilcon.  After 28 days, the highest activity was found on etafilcon and the lowest activity was on polymacon, lotrafilcon A and lotrafilcon B. 

The protein dynamics of tears are material-dependant and related to contact time, according to Aisling Mann and Brian Tighe (Biomaterials Research Unit, Aston University), who investigated the effect of a newly inserted lens on tear fluid composition and dynamics.  Lysozyme accounted for 35% of total tear protein detected on balafilcon A lenses, 34% for nelfilcon A, and 8% of the total tear protein on etafilcon A.

Gareth Ross and colleagues (Aston University) assessed the physical properties of silicone hydrogels worn and spoilt in an artificial tear solution.  Results showed that the properties of various materials vary widely: dynamic modulus ranges from 0.4 Mpa to 1.4 Mpa, coefficient of friction ranges from 0.04 to 0.15, and water content ranges from 24% to 47%.  Lathe-cut materials are able to combine Dk values in excess of 100 with water content of 32%. 

Lens wettability was the subject of a poster by Kunio Maruyama (Kyoto Prefectural University of Medicine), who measured interferometic contact angle and wettability associated with the appearance of a dry spot on the lens.  Wettability was significantly better in lotrafilcon A and B, balafilcon A, galyfilcon A and senofilcon A and the new Menicon lens) compared to the hydrogel lens.  The Menicon lens, lotrafilcon A, lotrafilcon B and balafilcon A had lower interferometric contact angles than galyfilcon A, senofilcon A and the hydrogel lens.