Issues and misconceptions about silicone hydrogel extended wear

Emmanuel Calligeros- Optometrist, Sydney, Australia
Emmanuel graduated with a Bachelor of Optometry in 1980 from UNSW and has been in
private practice in Sydney ever since. He has been active in both undergraduate and practitioner education, mainly in the area of contact lenses but also in the anterior eye and practice management fields. He has held key posts in optometric organisations in Australia and is a member of several advisory and review committees for the optometric profession.

Eyes of patients who have used PureVision for between one and two years on a continuous wear basis

It is now more than two years since I started fitting silicone hydrogel contact lenses, primarily for extended wear. Having fitted about 300 patients and been involved in a number of Bausch and Lomb Purevision workshops in Australia and New Zealand, I have compiled answers to the most commonly asked questions and misconceptions.

Why are the new silicone hydrogels safer than previous attempts at extended wear contact lenses? Previous attempts at extended wear contact lenses did not deliver sufficient oxygen transmission to prevent hypoxia. Equally important is the fact that when properly fitted the new silicone hydrogels do not adhere to the cornea and so allow adequate tear exchange to prevent build-up of toxins. The non-porous nature of the new silicone hydrogel lenses also minimises deposit build-up.

What type of patient is most suited to extended wear?
Successful daily wear patients who are looking for the ultimate in convenience. The most common reasons for failure are either fitting or tear quality related. Silicone hydrogels have also been useful for daily wear patients with high oxygen requirements, deposit problems or dryness problems with conventional soft lenses.

What is the most common wear regime recommended?
About half the patients I have fitted wear the lenses for 30 days continuously. The other half remove their lenses weekly or bi-weekly for a rub and rinse with a multi-purpose solution to minimise the build-up of toxins between the lens and the cornea. The frequency of removal is based on the quantity of mucin and lipid build-up between the lens and cornea.

What are the most common complications experienced with silicone hydrogel extended wear? I have observed sterile peripheral corneal ulcers in three per cent of patients, acute red eye in two per cent of patients and superior epithelial arcuate corneal lesions in one per cent of patients. The success rate of patients who make it through the first month trial is in excess of 90 per cent. All patients who experienced corneal ulcers and acute red eye were able to return to extended contact lens wear after a few days rest and with more frequent removal of the lenses for a rub and rinseusing a multi-purpose solution. I have not yet observed a microbial keratitis with silicone hydrogel extended wear.

Is comfort a problem with silicone hydrogels? Some patients who have previously worn thin medium to high water disposable contact lenses report initial discomfort with silicone hydrogels. This initial discomfort, which is probably caused by the relatively greater rigidity of the material, improves with adaptation, as does the tolerance of extended wear.

Does the surface quality of silicone hydrogels deteriorate with handling or wear? Silicone hydrogels gradually lose their wettability during a month of wear. There is no significant difference in the rate of deterioration between daily wear and extended wear. Protein deposits are not common on this type of material. Lipids and mucous deposits start to adhere to the surface only when it has deteriorated. The lens performance deteriorates rapidly after a month of wear.

Is lens performance affected by the environment? Silicone hydrogels out-perform conventional soft lens material in most environments. I have fitted a patient who successfully wore silicone hydrogels throughout a mountain climbing expedition in the Himalayas. The lenses also perform very well for scuba diving and in aeroplanes.

How important are lens lubricants in silicone hydrogel extended wear? Lens lubricants are commonly used on awakening to rewet the lenses and flush out any overnight muco-lipid build-up. Although I recommend lens lubricants to all my extended wear patients, some patients claim they make little or no difference to their comfort or tolerance of extended wear.

Is it safe to swim in silicone hydrogel extended wear contact lenses? Silicone hydrogel lenses are particularly suitable for swimming in the surf. Due to their rigidity, they do not dislodge as easily as conventional soft lenses. The risk of contamination is very low in the sea. On the contrary, I recommend goggles for swimming in pools due to the higher risk of contamination. Patients are warned to be very careful in spa baths where the risk of contamination is even higher.

*This article was originally published in the 2000-2001 edition of the Contact Lens supplement of the Australian Optometry magazine, and is presented here with their kind permission.