Silicone Hydrogels: At the Coal Face

I first became aware of the new generation of silicone lenses back in late 1997. I wrote about this emerging silicone-hydrogel technology in my online column IN CONTACT during the course of 1998 and 1999.

I was thus pleased when asked to become a clinical investigator for the new Purevision lenses in August 1999.

The one thing that became immediately obvious with these lenses were the beautiful, white, crystal-clear eyes that one noted, particularly if the patient had previously been using lower Dk disposables or conventional soft lenses.

Eye wearing Purevision© lens
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What soon became clear to me was that these lenses, when properly prescribed and managed, can provide outstanding results and patient's rave about them. I also learnt that careful patient selection is critical and thus I will share some of my experiences with these lenses - both Focus Night & Day and Purevision - in plus and minus, for extended wear, daily wear and monovision.

a) normal	b) engarged
Limbal vasculature
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As far as straightforward silicone-hydrogel extended wear [SHEW] is concerned I am still a practitioner who follows the 'Sunday lens' philosophy. In other words I fit the majority of my extended wear patients for six or seven night extended wear usage. Ideally they remove the lenses late on Sunday, clean and disinfect overnight, giving their eyes a one night break and revert to normal wear on the Monday morning. This has given exceptional results.

With time, as expected, I have noted a number of patients increasing their wearing nights up to two weeks, three weeks and often full thirty night extended wear, and sometimes more!

As we know a significant proportion of patients are non-compliant, hence my aforementioned philosophy: My rationale being that if we say seven nights extended wear they will probably wear them for fourteen nights. We have seen this with two-week disposable users who typically change them every four weeks and again with monthly disposable wearers often changing them at six weeks, eight weeks and even three months. I have even had a daily disposable [DD] wearer change their lenses every six to nine months!

Thus I believe in building in a safety margin; or in motoring terminology it's a little like a turbo 'pop-off valve' - so that we don't blow the whole thing.

Normal appearance of everted lid	Lid with CLPU
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The types of patients to eliminate from extended wear are in my opinion and experience, anyone with a history of GPC, inflamed lids, blepharitis, toxic tear syndrome and meibomian gland dysfunction. Some of these conditions can be successfully treated before embarking on extended wear however practically all my failures in patients I have discontinued have fallen into these categories - with previous or current histories of allergies, inflamed lids and ocular surface disease. A previous history or signs of corneal infection are also contraindications.

This does not however exclude these groups from the benefits of silicone hydrogels. They can be worn quite successfully - often better than existing soft lenses - on a silicone hydrogel daily wear [SHDW] basis.

I am now seeing fee-paying, real-live patients with over four years of extended wear in the new silicone hydrogel modality and am pleased to say that the majority of them continue to have crystal clear eyes, no sign of neovascularisation and their endothelia look excellent. I can only recall one case of seeing some mild striae following overnight extended wear. There have been a few SEALs and CLAREs - but I can count these on my two hands.

Most have been problem free.

SEALS
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Of the few cases of SEALs I have seen, these have generally been managed by fitting to an alternative brand and sometimes a different base curve. None have recurred.

Hyperopic monovision wearers have been delighted with the results but as reported we have been noting undesired orthokeratology in some patients in silicone hydrogel lenses. I have termed this phenomenon hyperkeratology where hyperopes, generally over +1.50D seem to shift into more hyperopia and this effect seems greater the higher plus we go. In monovision it is usually greater in the higher plus eye. I have had some benefit and improvement and partial reversal of this hyperkeratology in refitting to Purevision, which has a slightly higher water content and possibly a lower modulus, thus resulting in less corneal shape alteration?

Hyperopes stand to derive great convenience and benefit from extended wear in that they typically find handling lenses difficult due to the fact that they can't see them. A +4.00D hyperope that is presbyopic does not have the greatest near vision without lenses.

Likewise myopes find nothing better than being able to wake up in the morning and see the alarm clock or lie in bed and watch TV without having to get up and go to the bathroom, half asleep and fiddle around with lenses, storage and cleaning solutions.

Reducing or eliminating the amount of solutions in the eye has had some benefit in minimising so-called multi-purpose non-keratitis , which resulted in many symptoms of red and irritated eyes with conventional disposable and soft lens use.

Utilising the lenses for daily wear for complex cases, [e.g. high myopes with a history of neovascularisation and reduced wearing time and tolerance] is another use of these lenses. So is managing dry eye in the office - with computer users and air conditioning - in conventional disposable and soft lenses, where thin and high water content lenses can produce dry eye symptoms. With the low water content yet super-Dk of silicone hydrogels, significant benefit can be gained in these problematic environments.

I have also found major benefit in using these lenses for managing Dellen and vascularised limbal keratitis [VLK], where the bandaging effect of the lens minimises exposure dryness in this limbal area but at the same time the super-Dk allows the vessels to recede. Reductions in oedema, striae, neovascularisation, VLK, corneal steepening, endothelial changes and other symptoms and signs associated with chronic long-term hypoxia have been a boon for patients with extreme prescriptions in plus, minus and toric lenses, soft and RGP. They also make excellent piggyback and bandage lenses and are being used more and more following corneal trauma, debridement and even following refractive surgery.

These lenses can even be used for better management of non-compliant patients. A classic case would have been a young lad, son of a medical practitioner, who came into the practice regularly for many unscheduled visits as an abuser of conventional disposable lenses and solutions. Basically, he never cleaned and disinfected them as instructed and also never replaced them as he should have. He also tended to sleep in them and had regular occurrences of conjunctivitis and red eye. Since fitting him in silicone hydrogel extended wear lenses we hardly ever see him except for his scheduled visits and his eyes are looking considerably healthier, whiter and there are fewer inflammatory signs and symptoms.

Fortunately over the past few years I have not seen any cases of corneal ulcers [either sterile ulcers or microbial keratitis] in my patients but obviously there will always be such cases and colleagues have noted a significant number of sterile ulcers. A few MKs have also been reported. I did see one case of a chap who had been in a spa pool in San Francisco one night, caught a plane the next day from LA to New Zealand, and even though he had a red sore eye continued to wear the lens on extended wear. On getting off the plane in Auckland he had a significant central corneal ulcer which stained deeply into the stroma with fluorescein. He was immediately referred to an ophthalmologist. To date we have had no confirmation of whether or not it was an MK but the surgeon reported that it was a Uveitis - due to cells in the anterior chamber. I would however question that as I was called in by the examining optometrist and can confirm the significant corneal lesion. Cells would in all likelihood be present in the anterior chamber anyway as a result of a fairly deep central corneal lesion. Not the other way around.

I continue to recommend and prescribe silicone hydrogel lenses for all the previously mentioned cases and always caution users as to the necessity of strictly following the rules, removing the lenses immediately on any sign of abnormal symptoms, redness, discomfort, photophobia and so on. They are instructed to immediately consult an optometrist or ophthalmologist should any abnormal symptoms develop. Smokers and swimmers are also cautioned about the increased risk of problems in these situations and all patients are advised not to sleep in their lenses while suffering from any upper respiratory tract infection or other sinus/flu-like conditions.

We also counsel and advise hyperopic wearers that they might undergo a hyperopic shift, which may result in having to update spectacles and contact lenses. Forewarned is forearmed, but most accept that the benefit outweighs the risk.

We look forward to the next generation of silicone hydrogel lenses. Improved designs and lower modulus materials will hopefully minimise unintended corneal topographic changes, hopefully provide even greater oxygen, and may also include things such as UV absorption.

We also await with interest the first versions of extended wear toric and progressive contact lenses.

My compliments to all the developers, scientists, researchers, and clinicians who help bring this wonderful technology to market.