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This article is the second in a two-part summary of the 2007 Association for Research in Vision and Ophthalmology (ARVO) meeting which focused on ‘the aging eye’. Part one of this review concentrated on the effects of SH lenses on the ocular surfaces, measurement techniques, and current microbial/disinfection research. This article will report on the SH materials in relation to dryness, solutions and tear components.

In vitro dehydration of conventional and SH CLs was discussed in a poster by J.Gonzalez-Meijome et al who investigated lenses under various environmental conditions. They found that overall, HEMA-based hydrogel lenses dehydrate more, and faster than SH materials. No significant differences existed between conventional hydrogels and those that are claimed to reduce on-eye dehydration.

A comparative study of SH CL surfaces before and after wear using atomic force microscopy was undertaken by M. Lira et al. They used this equipment to analyse surface roughness of 3 SH lenses prior to and post wear. Significant increases in roughness were shown for galyfilcon over the course of lens wear, and also for balafilcon A though at a lesser extent. Lotrafilcon B lenses showed no significant differences in surface roughness.

A poster presented from D Luensmann et al from the University of Waterloo (Canada) investigated the use of confocal microscopy to determine albumin absorption and penetration into the matrix of hydrogel and SH lenses. Balafilcon A and senofilcon A lenses showed significant albumin absorption and penetration after 1 day. The absorption with lotrafilcon A remained low even after 14 days wear. Using confocal microscopy to observe albumin absorption and penetration showed significant differences between CL materials and has potential to indicate interactions between proteins with hydrogel biomaterials.

K.Maruyama et al from the Kyoto Prefectural University of Medicine investigated the potential uses of a new, interference-based in vitro technique for assessing the wettability of various CLs by use of an interferometer (DR-1TM; Kowa Co., Ltd., Tokyo). Their study used both rigid and soft lenses (SH and hydrogel with varying water contents) which had been pre-soaked in saline. Observations by the interferometer were then made to assess the interferometric contact angle (ICA) of the liquid layer attached to the lenses. The results showed that this could be a useful instrument for assessing the wettability of CL surfaces and for mimicking the wettability performance of CLs during actual use on the eye.

The activity of lysozyme deposited on various conventional and SH CLs as a function of time was investigated by L.N. Subbaraman et al using an in vitro model. Five SH and 4 conventional hydrogel lenses were examined over time periods ranging from 1day to 28 days. Total lysozyme and active lysozyme recovered from each of these lens materials were determined and the levels of denaturation found were highly variable between materials. The rate of reduction in the activity of lysozyme deposited also varied between the lenses examined.

R.L. Chalmers et al set out to determine the dryness symptoms that could be attributed to contact lens wear, via a comparison of symptoms from age-matched CL wearers and non-wearers. A historical, cross-sectional dataset of dry eye and CL dry eye questionnaires was used from an age matched subset of 259 CL lens wearers and 246 non-CL wearers. Prevalence of high frequency dryness ("frequent" or "constant") was compared between CL wearers and non-wearers. Longitudinal change in dryness frequency from 4 prospective studies (n=1,036) that involved refitting daily wear hydrogel lens wearers with SH lenses for daily or continuous wearing schedules was compared to the difference in symptoms between lens wearers and non-wearers.

After refitting daily wear hydrogel lens wearers with SH lenses, subjects reported approximately half the frequency of dryness during the day and end of day; an amount similar to the frequency of dryness symptoms of non-wearers.

A poster from W Nash et al also in the contact lens session investigated the major factors that determine protein and lipid deposition on 4 major silicone hydrogel lenses. The authors found that protein deposition was driven by both patient and lens related factors, but lipid contamination was shown to be due mainly to the lens material and tear/surface interfaces.

K.Nichols et al from Ohio State University, Columbus used mass-spectrometry and in vivo techniques to evaluate the changes in tear film caused by lipid deposition on hydrogel and SH lenses. Their results showed that SH lenses are likely to deposit more fatty acid amides, (primarily oleamide) than traditional hydrogel lenses, in-vivo and in-vitro. The authors conclude by recommending that the impact of this deposition on tear stability and lens wettability will need further exploration.