Academy 2006 was held in Denver, Colorado. Silicone hydrogel lenses generated much interest in the meeting, with 23 posters and 8 paper presentations.

Part 2 | Part 1

Tears, wettability, comfort and dryness
Zanna Kruoch (University of Houston) and colleagues compared the differences in tear exchange beneath various silicone hydrogel lenses to a single, commonly prescribed hydrogel lens material on eleven adapted soft contact lens wearers. Tear exchange rates were fastest with lotrafilcon A and took the longest time with galyfilcon. Lotrafilcon A and lotrafilcon B have a higher tear exchange rate than other lenses which is correlated with their higher modulus of elasticity in comparison with etafilcon A and other silicone hydrogels.

M-L Chantal Coles (Brennan Consultants) used rating scales to compare the comfort between  seven different types of soft contact lenses worn for a minimum of one month (seven different lenses : balafilcon A, etafilcon A, hioxyfilcon A, lotrafilcon B, omafilcon A, polymacon and senofilcon A). One silicone hydrogel (senofilcon A) outperformed the other lenses on all scales of comfort tested. The three mid-water content hydrogels generally performed better than the other two silicone-hydrogels (except for 30-day dryness for lotrafilcon B). The results also showed that Polymacon was the worst performing lens. All lenses except senofilcon A showed a decrease in comfort toward the end of the day after 30 days of wear.

Kathryn A Dumbleton, and co-workers at the Centre for Contact Lens Research investigated the initial comfort and adaptation of successful soft lens wearers refitted with five currently marketed silicone hydrogel lenses for daily wear. Results showed that initial comfort varied between silicone hydrogel lenses, however once settled no differences were found. The overall performance ratings for the silicone hydrogel lenses were high, however decreased comfort was noted later in the day for all lens types. Wearers of balafilcon A reported the lowest reported hours of comfortable wear. All ratings were obtained using BlackBerry™ wireless devices.

Jeffery M Schafer, (Ohio State University) and group showed that dryness symptoms in low Dk/t hydrogels improved after refitting with lotrafilcon A. This improvement was noticed after 1 week of lotrafilcon A lens wear and was maintained throughout the 3 years of the study. In many lens wearers, refitting with silicone hydrogel lenses reduced the frequency and severity of dryness symptoms that were present during low Dk/t hydrogel lens wear.

Robin L. Chalmers (Private Practitioner) and co-workers evaluated the effect of climate changes on ocular surface symptoms with hydrogel and 2nd generation silicone hydrogel lenses. The authors found no difference in the frequency of ocular surface symptoms reported in winter, among subjects who wore hydrogel lenses in cold or milder climates. Refitting the subjects with second generation silicone hydrogel lenses reduced the frequency of all ocular surface symptoms tested among those living in cold climates.

Using an in vitro model, Heather Sheardown and Liu (McMaster University) studied the wetting agents (such as PVP) incorporated in non-surface modified silicone hydrogel lens materials (galyfilcon A and senofilcon A). They studied if PVP remains within the lens or if they are released into the ocular environment. Their results showed that senofilcon A lenses (with HYDRACLEAR™ Plus technology) did not release PVP, whereas galyfilcon materials (with HYDRACLEAR™ technology) leach PVP in an amount consistent with packing solution components.

Deposits
Andrew Emch, (Ohio State University) and colleagues compared the protein deposition on two silicone hydrogel lenses (lotrafilcon B and galyfilcon A) with the use of different four care solutions (AQuify, Complete MoisturePlus, OptiFree Express Replenish, and ReNu MoistureLoc). They reported that over 50% more protein was recovered from lotrafilcon B compared with galyfilcon A after a day of wear, and that this was consistent for three of the four care solutions. The authors concluded that OptiFree Replenish generally removed the most protein from both lens types.

Lakshman Subbaraman (Centre for Contact Lens Research) and colleagues compared the lysozyme uptake kinetics on silicone hydrogel, FDA Group I, Group II, Group IV and PMMA contact lens materials by incubating lenses in 125I-labelled lysozyme. Lysozyme deposition occurred rapidly with Group IV lenses before reaching a maximum while silicone hydrogel, Group I, Group II and PMMA materials progressively accumulate lysozyme, with no plateau during the time period tested.

Maciej Suwala (Centre for Contact Lens Research) and co-workers investigated the quantity and conformational state of lysozyme deposited on conventional and novel silicone hydrogel lenses using an in vitro model. The results from this study showed that the silicone hydrogel lenses deposit lower amounts of lysozyme than either conventional FDA group II or group IV lenses, and the levels of activity of lysozyme are highly variable between materials.

Doerte Luensmann (Centre for Contact Lens Research) and co-workers used confocal microscopy to examine the depth of penetration of fluorescently-labeled albumin into etafilcon A and lotrafilcon B lens materials at the end of 1, 7 and 14 days. They found that there was no increase in deposition between days 1 and 14 with lotrafilcon, but surface deposition on etafilcon increased between days 1 and 7. Significant levels of albumin were detected within the matrix of etafilcon after as little as 1 day, but no albumin was detected in the matrix of lotrafilcon at any time.

Solutions
Michael A. Ward (Emory University School of Medicine) and Joseph T Barr presented a workshop on current lens care products, highlighting differences in those available, technological advances and compatibilities referring to both HEMA and silicone hydrogel lens materials. Solution component actions, compliance benefits and possible complications were discussed and illustrated through a variety of case reports.

Daniel Tilia (University of New South Wales) and colleagues evaluated the solution toxicity associated with a hydrogen-peroxide based system, and four polyquaternary ammonia/biguanide based systems when used with a range of marketed silicone hydrogel lenses. The authors showed that the hydrogen peroxide based solutions performed most favourably irrespective of contact lens type, producing the lowest rates of toxicity.

Kathryn A Dumbleton, and co-workers at the Centre for Contact Lens Research evaluated the performance of a no-rub hydrogen peroxide care regimen that incorporates a surfactant (Clear Care® CIBA Vision®) when used with 5 currently marketed silicone hydrogel lenses. No difference was found in the pre-lens non invasive tear break up time, or the degree of staining between lens types in this 5 month clinical trial. Graded wettability was superior and visible deposition was lower with lotrafilcon A and B lenses, than balafilcon A, galyfilcon A and senofilcon A.

Staining studies
Using Fluorescein and Lissamine Green stains, Jalaiah Varikooty (Centre for Contact Lens Research) and colleagues were able to identify five different clinical patterns of upper lid margin staining. The patterns which were noted in silicone hydrogel lens wearers included: vertical streaks, short horizontal band, speckles, comb-shaped and thick horizontal band.

Sruthi Srinivasan (Centre for Contact Lens Research) and co-workers examined the lid margin of certain silicone hydrogel lens wearers who reported symptoms of dryness. They reported that the fluorescein and lissamine staining took on an atypical fimbriated appearance extending from the margin into the tarsal plate.

Noel A. Brennan, (Brennan Consultants) studied the effect of silicone hydrogel lenses worn on a daily wear basis on the conjunctiva by lissamine green staining. 116 subjects wearing various different soft contact lenses were enrolled in the study. Conjunctival splits and fringes were noted in silicone hydrogel lens wearers, the risk factors for which were found to be closed-eye wear, edge design and material modulus. The marketed balafilcon A lens, which has a rounded edge design, rarely produces this effect. The authors suggest that the results of this daily wear are consistent with the concept that this edge design presents the least impact on the conjunctiva.

Adverse events
Arthur P Back and co-workers (CooperVision, Inc.) evaluated the rate of corneal infiltrative events and SEALs in a newly developed silicone hydrogel contact lens (Biofinity), compared to currently marketed continuous wear lenses lotrafilcon A and balafilcon A). The authors showed that the overall rate of corneal infiltrative and SEAL events was similar for the Biofinity and lotrafilcon A lenses, while the balafilcon A rate was significantly higher.

Chun-Yee Jenny Lung and H .Y. Ng, (The Hong Kong Polytechnic University) reported an unusual case of severe diffused corneal dry spots, which were noted in an asymptomatic conventional hydrogel contact lens wearer (Polymacon) when they were switched to a silicone hydrogel lens material. The authors reported that the dry spots on both corneas disappeared after discontinuation of contact lens wear for one week.