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The 2007 Association for Research in Vision and Ophthalmology (ARVO) meeting focused on ‘the aging eye’. The subject of silicone hydrogels (SH) was well represented by 21 papers and posters which will be summarised in this 2 part review.

Downtown Fort Lauderdale, Florida, USA

The contact lens poster session provided the most information into different aspects of SH lenses including surface characteristics, and efficacy of care solutions. Part 1 of this summary will concentrate on the effects of SH lenses on the ocular surfaces, measurement techniques, and current microbial/disinfection research. Part 2 will report on SH materials and the effects of solutions and tear components.

Ocular surface diseases and therapy session
In the ocular surface diseases and therapy section, a poster presented by J.Ogawa et al from Keio University (Japan) described the ‘Therapeutic applications of soft contact lenses (CLs) in severe dry eye with chronic graft-versus- host disease (cGVHD)’. They used SH lenses to bandage 7 subjects with cGVHD and found that their discomfort was significantly reduced and the tear film was stabilized.

During the same session S.Zhang et al from Georgia State University, Atlanta presented work into the ‘Firm attachment to and penetration of SH CLs by representatives of Fusarium Oxysporum - F. Solani complexes’. They exposed SH lenses to isolated strains of the Fusarium complexes and examined the degree and time taken for penetration of lenses when multipurpose solutions were introduced. They concluded by demonstrating that Fusarium strains were equally affected by solutions containing PBS and Renu MoistureLoc.

Contact lens poster session
C. Radford et al presented the results of a 2 year prospective study into the relative risks of acute, non-ulcerative complications (NUC) with contemporary CL wear. Data were taken from Moorfields Eye Hospital with CL related-disorders other than microbial keratitis. There were 877 cases of NUC examined in comparison to controls. The risks for any non-ulcerative complication was similar between CL types used for daily wear, while extended wear of any soft lens increased the risk by two to four times. SH lenses were associated with a significantly greater risk of mechanical disorders.

L. Santos et al from the University of Minho (Portugal) presented a study into the influence of wear on bacterial adhesion and disinfection to SH CLs. Worn and unworn CL were colonised by a clinical strain of Staphylococcus. The efficacy of ReNu MultiPlus in detaching adhered cells and the percentage of remaining dead cells was determined for 4 SH lenses and Etafilcon A. Their results showed that worn SH CLs were equally or less prone to microbial adhesion than unworn lenses, whereas worn conventional hydrogel CL exhibited a greater extent of microbial adhesion. The reason for this was suspected to be changes in lens surface hydrophobicity which are modified during wear.

The antimicrobial efficacy of currently marketed lens disinfecting solutions against Fusarium solani (in the presence of silicone and conventional hydrogel contact lenses and lens cases) was examined by M George et al. They aimed to investigate the International Standards Organisation (ISO) test of solutions efficacy with combinations of solutions and from soak and dry cycles of lens cases and lenses. It appears that the introduction of lenses to the ISO test against Fusarium reduces the efficacy of multipurpose solutions. They conclude by suggesting that solution compatibility with lens and lens case materials warrants investigation during the solution development process.

I.Cox et al measured the upper and lower tear menisci on contact lenses using real time optical coherence tomography (OCT). They measured changes in meniscus height with 20 subjects wearing balafilcon A on one eye and galyfilcon A on the other eye. The menisci around both eyelids immediately increased after lens insertion p<0.005 and recovery to baseline was determined for both eyes after 20 minutes of lens wear. This poster demonstrated that the OCT could be used to examine and compare tear menisci.

From the University of New South Wales M.Markoulli and colleagues discussed the clinical characteristics and resolution of conjunctival flaps. Twenty-eight events of conjunctival flaps observed during extended wear of SH CLs were monitored until resolution. The study concluded that they resolve spontaneously with discontinuation of CL wear. Further studies are required to ascertain whether these events have any significance to the success of contact lens wear.

From the Southern California College of Optometry, J.Hall et al assessed whether measures of epithelial barrier function can objectively quantify any potential lens-solution bio-incompatibilities. Six subjects were re-fitted into SH pre-soaked in 1 of 3 solutions which included either polyquaternium-1, PHMB or non-preserved saline. A wide range of fluorescein dye penetration was observed suggesting that although the equipment is sensitive, more work is required to determine significance.

C. Skotnitsky et al examined the incidence of CL induced papillary conjunctivitis (CLPC) in low and high Dk lens wearers. Data from 517 patients from Australia and 1,040 patients from India were collated. The incidence of CLPC with low Dk versus high Dk SH lens wearers was found to be similar (p>0.05). However, a higher incidence of local CLPC was found for the SH wearers, and a higher global CLPC for low Dk wearers (p<0.001). The authors concluded that this could be due to differences in modulus, responses to protein deposition, and also lens design.

From Brennan Consultants, Auburn Village (Australia) M. Coles-Brennan et al presented a poster which reported on the change in limbal redness following overnight wear of SH lenses. Eight subjects were recruited and were assessed by the grading of limbal redness (Efron scale) and measures of corneal thickness (Orbscan) prior to and post overnight wear of one of 3 SH lenses. The authors conclude that closed-eye wear of the SH lenses produced a significant limbal response which correlated with both corneal swelling and local Dk/t measures (which were recently determined at central and peripheral lens positions).

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