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HomemieyecareThe Perfect Contact Lens

The Perfect Contact Lens

The invention of the contact lens revolutionised the vision correction industry, offering consumers a convenient and effective alternative to spectacle wear. More recently, some major innovations have led to significant improvements in the ability of contact lenses to provide quality vision correction for a range of disorders, while also improving comfort and safety.

The Institute for Eye Research has a strong history in the area of contact lens research and development and we are now striving to create the next generation of lens for consumers – the most comfortable, biocompatible lens yet, that also provides superior vision correction.

The Institute’s Perfect Contact Lens programme has developed silicone hydrogel contact lenses that are an excellent fit for the eye and provide exceptional vision correction along with the highest possible level of oxygen to the cornea so that hypoxic complications are minimised.

Further improvements will result in comfortable wear and reduced inflammatory complications, especially those that occur as a result of increasing bacterial burden.

The programme is investigating a host of factors that impact on contact lens performance and ocular health, including development of antimicrobial contact lenses, determining the efficacy of contact lens solutions, examining the role of genetic factors in the incidence and severity of microbial keratitis, and investigating the role of the tear film in lens comfort.

Microbial keratitis epidemiology and development of antimicrobial contact lenses.

Contact lens wear, especially extended wear, is associated with an increased risk of corneal infection and inflammation, caused by bacterial contamination of the contact lens surface. Microbial keratitis is a corneal inflammation caused by bacterial infection and the most severe complication of contact lens-related eye infection. Microbial keratitis is often associated with contact lens wear, although it can occur subsequent to trauma to the eye or as a result of underlying diseases such as thyroid disease.

Although cases of microbial keratitis are very rare (for overnight wear silicone hydrogel lenses the rate is 25 in 10,000 for daily wear rigid gas permeable lenses the rate is 1 in 10,000 and only 10-15 per cent of cases result in permanent vision loss1), its serious implications has led the Institute to undertake a range of projects to enhance our understanding of the etiology and treatment of this infection. By developing an antibacterial contact lens that prevents bacterial adhesion we are hoping to reduce the occurrence and severity of infection and inflammation caused by microbial keratitis.

One such project is examining the ability of selenium-coated contact lenses to control the adhesion of bacteria to the lens surface. Our bodies require selenium for normal metabolic function and its other properties include an ability to produce oxygen radicals. These are a very reactive oxygen species, acting to oxidise most things very effectively, including bacteria, which are highly susceptible. So far, our results in this area have been promising, demonstrating that selenium-coated lenses can prevent colonisation of the surface by bacteria.

The Institute is also investigating ways to minimise inflammation associated with contact lens wear. Bacterial compounds called quorum-sensing molecules allow bacteria to communicate with each other and form impenetrable biofilm surfaces that make bacteria resistant to antibiotics. Fimbrolides (also known as Furanones) are quorum-sensing inhibitors that disrupt this bacterial communication. The Institute is testing the antibacterial efficacy of these compounds once attached to contact lens surfaces.

Some of these new antimicrobial lens systems have been tested in short term clinical trials and been shown to be safe for wear during sleep. The Institute is now scaling up various forms of the antimicrobial lenses for further clinical evaluation.

Contact Lens Solutions

Developing our understanding of how contact lens solutions act against different bacteria implicated in contact lens-related infection is another important area of research. The bacteria Serratia marcescens and the fungus Fusarium solani have been implicated in a range of ocular adverse events, including endopthalmitis, keratoconjunctivitis and contact lens related keratitis.

In order to investigate the efficacy of contact lens solutions, we are studying susceptibilities of clinical isolates of these microbes in various contact lens multipurpose disinfection solutions to determine if some solutions might predispose contact lens wearers to greater risk of infection.

Indeed, we are benchmarking the effectiveness of currently commercially available contact lens disinfecting solutions and using clinical isolates of bacteria, fungi and Acanthamoeba to further investigate their usefulness.

The Tear Film

The tear film possesses a number of properties allowing the tears to perform a crucial role in maintaining ocular health, including lubricating and protecting the eye. The tear film’s lipid layer is vital in preventing excess evaporation of the aqueous phase, a major cause of ‘dry eye’. Dry eye causes a range of conditions leading to discomfort and in severe cases may result in vision loss. It is also one of the main reasons wearers abandon their use of contact lenses.

Phospholipids are thought to act as a surfactant to spread hydrophobic lipids across the surface of the eye. Lipids and proteins can form deposits on the surface of contact lenses which may lead to unwanted side effects ranging from discomfort to frank adverse events such as contact lens-induced papillary conjunctivitis (CLPC) – an allergic reaction of the cornea caused by toxins produced by bacteria on the contact lens surface.

The exact composition of the lipids in the tear film is not known. Consequently, the Institute is seeking to characterise the lipidome of the tear film, and to identify which lipids deposit onto contact lenses. Researchers are also examining whether particular lipids are involved in the production of dry eye or adverse responses during contact lens wear.

Mucins occupy a vital part of the tear-film and play various important roles, such as maintaining viscosity and lubrication to retard fluid evaporation and anchoring the aqueous tear-film to the underlying cornea and conjunctival surface. In addition, mucins in tear fluid also show protection against pathogens by interaction with various microbes due to the densely glycosylated surface of the mucins.

Finally, we have discovered that there are perhaps other mucin-like components of the tear film and are currently investigating the biochemical nature of these components and attempting to identify their role in tear film physiology.

These investigations are not only crucial components of a long-term programme to develop the ‘perfect contact lens’. The knowledge accumulated from this research makes a valuable contribution to our understanding of the physiology of the eye and ocular health.

Professor Mark Willcox, BSc PhD, is Chief Scientific Officer at the Institute for Eye Research, Professor of the School of Optometry and Vision Science, University of New South Wales and Executive Director of Science and Core Capabilities at the Vision Cooperative Research Centre.

References
1.Stapleton F, Keay L, Edwards K, Naduvilath T, Dart JK, Holden BA. The Incidence of contact lens-related microbial keratitis in Australia. Opthalmology 2008 Oct; 115 (10): 1655-62

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