By Dr Chantal Coles-Brennan
Manager Medical Affairs, Johnson & Johnson Vision Care
The contact lens industry and optometric scientific community have long been interested in the interaction between the tear film and contact lens materials. It is well established that most of silicone hydrogel materials are prone to lipid deposition whereas hydrogels are more likely to attract proteins from the tear film.
In vitro studies have shown that lysozyme is the major protein that deposits on hydrogels, accounting for approximately 40 per cent of all proteins found in the tear film.1,2 Lysozyme is a beneficial protein in the tear film and is involved in the eye’s natural defence mechanism.
Lysozyme is a positively charged enzyme produced by the lacrimal glands and exists in the tear film in its active or ‘native’ state.
The introduction of a contact lens to the ocular environment and the subsequent deposition of lysozyme can induce structural changes to the protein, leading to a loss in the enzymatic activity. This is called inactive or ‘denatured’ state.
The quantity and quality of proteins deposited on contact lenses are influenced by a number of factors, including water content, material charge (ionic or non-ionic) and pore size, chemical composition, and density of the lens matrix. Both are also influenced by surface modifications and the type of care regimen used.3,4
Etafilcon A is an anionic (negatively charged) high water content material (group 4 material). It is known to rapidly and selectively attract high levels of lysozyme from the tear film.5 The unique chemistry of etafilcon A material allows lysozyme to flow loosely and reversibly through the lens matrix, retaining more than 90 per cent in its native state.
For low water content, non-ionic materials, lysozyme is mostly present on the lens surface.
Over time the bound protein becomes denatured and is unable to perform its original function. This may trigger an immunological response resulting in allergic reactions such as contact lens induced papillary conjunctivitis.6
Recent in vitro* studies using the latest state of the art techniques, demonstrated that denatured lysozyme alters the metabolic activity of human corneal epithelial cells (HCEC) and triggers the release of inflammatory biomarkers in the surrounding medium.
It is a dose dependent response. The greater the amount of denatured lysozyme is exposed to the cells, the higher is the release of the inflammatory biomarkers from the HCEC. The relationship between the inflammation signalled by the release of biomarkers and irritation is well established.
This research further demonstrated the unique ability of etafilcon A to maintain low levels of inflammatory biomarkers released by the corneal epithelium.
Etafilcon A is the material used in the 1-Day Acuvue Moist series of daily disposable lenses, which will soon be available for presbyopia, and be launched in Australia in 2015.
* Based on in vitro data; clinical studies have not been done directly linking differences in lysozyme profile with specific clinical benefits.
- Leahy CD et al. Initial in vivo tear protein deposition on individual hydrogel contact lenses. Optom Vis Sci 1990: 67: 7: 504-511.
- Zhao Z et al. Proteomic analysis of protein deposits on worn daily wear silicone hydrogel contact lenses. Mol Vis 2008: 14: 2016-2024.
- Suwala M et al. Quantity and conformation of lysozyme deposited on conventional and silicone hydrogel contact lens materials using an in vitro model. Eye Contact Lens 2007: 33: 3: 138-143.
- Senchyna M, Jones L, Louie D, May C, Forbes I, Glasier MA. Quantitative and conformational characterization of lysozyme deposited on balafilcon and etafilcon contact lens materials. Curr Eye Res 2004; 28: 25-36.
- JJVC Data on file 2014.
- Morgan P. Tear film proteins: Examining production, role and interaction with contact lenses. Contact Lens Spectrum, April 2010.