Prevention of Bacterial Colonization of CLs with Covalently Attached Selenium & Effects on the Rabbit Cornea

Percy Lazon de la Jara, B.Optom,PhD, FIACLE, Head of Clinical Research, IER, Sydney Australia Dr Percy Lazon is an optometry graduate from the Escuela Superior de Optica y Optometria and Universidad Peruana Los Andes in Lima, Peru. After 5 years working in private practice and as a contact lens educator at the School of Optometry in Lima, Peru, Dr Lazon joined the International Association of Contact Lens Educators (IACLE) where he was Regional Coordinator for Latin America for ten years. Dr Lazon completed his PhD on the topic “Quality of Life and Vision after LASIK” with the Vision Cooperative Research Centre in 2005. From 2005, he was Project Director at the Institute for Eye Research before taking up his current role as Head of Clinical Research in February 2009.

Mathews SM, Spallholz JE, Grimson MJ, Dubielzig RR, Gray T and Reid TW,  Cornea 2006;25:806-814

Currently, there is increased effort devoted to reducing the levels of microorganisms in the contact lens system (contact lenses, lens cases and lens solutions), with the ultimate goal of decreasing the incidence of many ocular adverse events related to contact lens wear. Recent recalls of contact lens solutions associated with ocular infection outbreaks around the world need to be taken as a wake-up call that the presence of microorganisms plays an important role. The application of antimicrobial surfaces to medical devices is not new; its main purpose is to kill microorganisms and to prevent biofilm formation. This technology has been widely applied to catheters, spinal shunts, heart valves, stents, etc., with high success, and can be the next step in our battle against microorganisms. 
In the contact lens field, where compliance is an important factor in reducing the incidence of complications and is highly patient-dependant, a passive mechanism such as antimicrobial surfaces for contact lenses and lens cases is a viable and excellent option to increase safety and efficacy of contact lens wear.  The ability of microorganisms to form a biofilm on a contact lens or the surface of a contact lens case has been reported widely (1). Moreover, the biofilm may function as a reservoir for pathogenic bacteria (2).

Selenium (Se) has potential applications for safer contact lenses.  Se is an essential part of our diet, playing an important role in the production of antioxidant enzymes and promotion of immune function. It is also able to kill microorganisms by forming superoxide radicals that are toxic to bacteria and viruses.

A selenium-based antibacterial contact lens surface is explored in a 2006 paper written by Mathews et al. (3). The purpose of this work was to test the safety and efficacy of a selenium-coated silicone hydrogel lens (balafilcon A) in a contralateral, two-month continuous contact lens wear, animal model study with no masking.

Commercially-available PureVision lenses were covalently coated with Se and evaluated after up to two months of wear in a rabbit eye. The rabbit corneas were assessed with a slit-lamp for clinical findings such as hyperemia, neovascularization, edema, infiltrates and staining. Changes in corneal thickness were evaluated. Furthermore, morphology and histopathology of the rabbit corneas were examined for signs of possible toxicity caused by the Se coating. Finally, in a subset of worn contact lenses, the amount of protein and lipid adherence to the lens surface was analyzed.  In a separate in vitro experiment, the investigators challenged control and test lenses for bacterial adhesion, inoculating a high bacterial load of P. aeruginosa at a log-phase growth.

The authors found no significant differences in clinical signs, epithelial and corneal total thickness, corneal morphology and corneal histology between control and tests corneas.  However, a trace level of corneal staining was reported for the control and test eyes. There was no significant difference in total protein and lipid deposition between worn lenses, and the Se-coated lenses showed resistance to colonization by P. aeruginosa when compared to the untreated lenses in vitro. The authors concluded that these findings present strong evidence that the Se-coated lenses do not cause damage to the rabbit corneas after two months of continuous wear.

These results clearly demonstrated that Se coated lenses showed a marked inhibition of P. aeruginosa colonization in vitro and that the rabbits were able to wear the contact lenses for two months consecutively without the presence of adverse events. These results are quite encouraging.
However, some questions remain unanswered. For example the efficacy of Se-coated lenses in reducing or killing a wide variety of microorganisms commonly isolated from different inflammatory and infectious ocular conditions, such as gram positive and gram negative bacteria, fungi, protozoa, etc. The biocompatibility of any coating strategy with current contact lens materials and contact lens solutions on the ocular surface, and any possibility of allergic reactions must be studied. Moreover, there may be an effect on the normal ocular microbiota, which may protect the eye from colonization by potential pathogens. The ideal antimicrobial strategy should target pathogenic microorganisms while having little effect on the normal ocular microbiota, but this is not an easy task.

REFERENCES

1. Bacterial biofilm on contact lenses and lens storage cases in wearers with microbial keratitis. McLaughlin-Borlace L. Stapleton F. Matheson M. Dart JK. Journal of Applied Microbiology. 84(5):827-38, 1998.
2. Bacterial transmission from lens storage cases to contact lenses-Effects of lens care solutions and silver impregnation of cases. Vermeltfoort PB. Hooymans JM. Busscher HJ. van der Mei HC. Journal of Biomedical Materials Research. Part B, Applied Biomaterials. 87(1):237-43, 2008.
3. Mathews SM, Soallholz JE, Grimson MJ, Dubielzig RR, Gray T and Reid TW, Prevention of bacterial colonization of contact lenses with covalently attached selenium and effects on the rabbit cornea, Cornea 2006;25:806-814.
4. Kirisits MJ, Parsek MR. Does Pseudomonas aeruginosa use intercellular signalling to build biofilm communities? Cell Microbiol 2006;8: 1841–9.
5. Zhu H. Kumar A. Ozkan J. Bandara R. Ding A. Perera I. Steinberg P. Kumar N. Lao W. Griesser SS. Britcher L. Griesser HJ. Willcox MD. 2008. Fimbrolide-coated antimicrobial lenses: their in vitro and in vivo effects. Optom Vis Sci. 85:292-300.
6. S. Nissen,· FH Furkert. Antimikrobielle Wirksamkeit einer Silberbeschichtung von Hydrogellinsen. Ophthalmologe. 2000: 97:640–643