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PhD candidate, Jennifer Choo,
has proved that
Orthokeratology contact
lenses that are only worn
overnight and provide clear
vision throughout the day are
safe to use.

New contact lenses that can be worn overnight and then taken out in the morning to give you clear vision throughout the day are becoming increasingly popular.

But reports of increased infection rates have made many potential patients wary.

Luckily for them, recent research at the Vision Cooperative Research Centre has shown that the new lenses don’t make the eye any more prone to infection.

Jennifer Choo, who is undertaking her PhD research with the Vision CRC, has released her work on “Corneal Changes Induced with Orthokeratology Lens Wear” in Sydney on 20 May 2008.

“Orthokeratology, or OK, lenses are purposely designed to reshape the surface of the cornea (the front of the eye) overnight while the patient sleeps. Upon awakening and removing the lenses, patients then experience clear vision without the need for glasses or contact lenses. This provides a wonderful vision correction option for many patients and it is growing in popularity”, says Dr Choo.

“Unfortunately, a number of severe infections recently reported in patients wearing OK lenses has raised concerns about the safety of purposely altering the corneal tissue. The critical question is whether these changes are predisposing the eye to an infection by compromising the cornea’s natural defensive barriers to microbial infection.

“Our work has explored this important question with studies using specially designed OK lenses for cats, enabling us to see and understand the cellular changes induced by the lenses.”

The research found that dramatic alterations in the thickness of the outermost layer of the cornea – the epithelium – occurred. Normally the epithelium is rather uniform in thickness across the cornea, however with these lenses there is epithelial thinning in the centre and thickening in the mid-peripheral region.

To then determine if manipulation of this epithelial layer was making the eye susceptible to infection, the cornea was exposed to very high levels of bacteria through a variety of challenges.

“We found that despite the dramatic changes in the tissue with this procedure, the corneal defenses are still intact and these changes did not predispose the eye to infection,” said Dr Choo.

“This is a very important result, and paves the way for safe use of this form of vision correction.”

This research has also added to our understanding of how the cornea reacts to contact lens wear in general.

Ordinary contact lenses are a successful and preferred choice of vision correction for millions of people worldwide. However, this product is not without its complications, the most serious of which are eye infections. While the incidence of this condition is quite low due to the incredible defenses of the eye, the potential to cause permanent vision loss makes this condition of real concern to the millions of contact lens wearers worldwide. Approximately 10-15 per cent of cases are associated with some loss of vision.

“The current understanding of how contact lenses make the cornea more susceptible to infection is lacking”, said Dr Choo. “Our OK research has provided valuable insight into understanding contact lens related infections and the mechanisms underlying microbial infections.