In Contact - July 2009

Tru, Blu & Nu

By the time you read this we will have had the official launch of the long awaited, world first single-use silicone hydrogel contact lens, 1 Day Acuvue TruEye.
I first predicted a one day silicone hydrogel lens in a presentation at the European Research Symposium in Berlin, 2000 less than a year after the launch of B&L?s PureVision and CIBA?s Night & Day breakthrough si-hy lenses. I've also previously reported on the lens and surprise launch of TruEye at the BCLA in May 2008.

Australia, New Zealand and Hong Kong are now the only other markets outside of the UK to thus far have access to this unique one day si-hy lens.

It seems most of us agree that ?shorter is better?: The avoidance of all the nasties associated with re-usable lenses is the ideal scenario. We also eliminate solution-lens related corneal staining associated with multipurpose disinfecting solutions and get rid of grody and potentially contaminated contact lens storage cases.

All in one fell swoop.

We also note that research has shown that one day lenses are dramatically safer than any form of soft lens extended wear, whether si-hy or conventional hydrogels. The overall safety profile of one day lenses is only beaten by RGPs.

Viva RGPs.

Although one study found that single use lenses have a slightly higher relative risk of MK than ?planned replacement? lenses there seemed to be some confounding factors. MK rates also varied between daily disposable lens brands. In my humble, anecdotal, clinical opinion I would say that the incidence of red eye and problems associated with dailies is lower than any other soft lens modality. I am unaware of any cases of MK among my daily disposable wearers.
For at least the past decade we have been able to avoid most nasties, very successfully and safely, with regular one day lenses. Although these lenses generally meet the Holden-Mertz Dk/L levels for safe oedema free daily wear in lower powers, most regular hydrogel dailies drop below these levels at higher plus and minus powers. As we know, their profile Dk/L doesn?t meet the required standard. The rare detractors of the one day modality were quick to point this out.

I would imagine this last line of resistance has now been removed?

The way I see it there's no longer much reason not to switch to a single-use lens modality. I'm sure the other major manufacturers will follow suit and also ramp up production to achieve economies of scale and launch daily versions of si-hy lenses. We may also see bacteria-resistant lens surfaces appearing in dailies.
Will we see drug releasing dailies?
Extended power ranges to match the current +6.50 to -12.00D dailies? spread are also on the cards for single use si-hy lenses, with a variety of base curves and diameters. No doubt we?ll see astigmatic and presbyopic versions in time.

One question raised by the Devil?s advocates is that there is some concern that high Dk versions of daily lenses will encourage extended wear of one day lenses.
I see it differently.
Single use lenses will be promoted and recommended exactly as that. Wear for a day and throw away. On the other hand we all know that some single use lens wearers already sleep in their lenses ? contrary to instructions and indications - which in no way meet the Holden-Mertz criteria for oedema free, ?safe? extended wear. Some studies show that the risk of MK with EW does not seem to be any better with si-hy lenses than conventional hydrogels. It seems EW is the risk factor, not Dk per se.
I thus prefer it if someone who abuses dailies, and wears them on an EW basis, has a decent level of closed-eye corneal oxygenation, rather than a compromised level that induces oedema through hypoxia. Low-Dk EW abuse only serves to increases the risk of refractive and topographic changes as well as potentially damaging endothelial cells, promoting neovascularisation and other complications associated with sub-par levels of corneal oxygen.

My results so far on limited clinical trials with TruEye have been very promising with high levels of comfort and acceptance. Some patients have reported them as ?the best daily disposable ever? and most have shown the nice clear, white eyes we have come to accept as the norm for high Dk si-hy lenses. Others rate them as comfortable and easy to handle. Additionally they report great all day comfort and stable vision. Of course there's no contact lens that's a panacea. There have been and will be a few patients who prefer their original Moist lenses, or prefer to continue with other lens brands, although I'd encourage high Rx wearers to switch.
There will also be a few of what I call ?silicone-responders?: Those patients that seem to develop or show an initial ?allergic? reaction to silicone-containing lenses. As stated a decade ago when I performed the first silicone hydrogel trials, I'd shy away from fitting those that show signs of inflammatory lid conditions, blepharitis and so on. They are often the clich?d blonde, blue eyed patients with pinkish lid margins and a history of allergies, eczema and dermatitis.
Of course it happens to brunettes too.

I do however expect the majority of suitable wearers will benefit from and succeed with one day silicone hydrogels.

 

Hybrideyez?


I have also finally managed to get my hands on a SynergEyes hybrid contact lens fitting set. It's been a long, frustrating wait of around three years.
I initially made contact with Jerry Legerton, co-founder of SynergEyes and developer of this current form of higher Dk hybrid technology, way back in the early stages of development. Although he has since left the company I remained in contact with the company and also with those familiar with its fitting and usage. As far as I understand the situation, SynergEyes was funded with private equity money and the company understandably wanted to get it up and running, successfully and profitably, in their home market of the USA before launching in other markets. At this stage they are not rolling it out on any widespread basis in this part of the world.

I'm still getting familiar with the fitting system and have only ordered lenses for one of my patients at this stage. I've performed a few other trials that I did not proceed with. In one case, with a graft in one eye, the fit was unacceptable and I did not want to aggravate neovascularisation ? present to the graft-host junction - as the SynergEyes lens still has a low Dk HEMA-like skirt. The 100Dk RGP section is however streets ahead of the dare I say it, obsolete former hybrid lens that's been around for a decade or two. I hear via the grapevine that a hybrid with a high Dk si-hy skirt is under development. I also hear from some with SynergEyes experience that it is, as expected no cure-all. Although it helps achieve decent results for some, there are still issues with hypoxia and lenses can become unacceptably tight over time. There are also limitations on what constitutes a satisfactory fit and the company, quite correctly does not encourage fitting lenses that do not meet their clear guidelines.
Various SynergEyes ranges are available for astigmatism, keratoconus, presbyopia and post surgery. An advanced KC design called ClearKone has also recently been released. At this stage I am mostly interested in the KC and ClearKone versions for RGP intolerants. For many patients RGPs achieve excellent results and si-hy lenses often do the trick.

RGPs provide quality vision and are still the best, safest, most economical contact lenses. To this day I still have many RGP wearers who prefer them to soft lenses. Their only real downside is in windy, dusty conditions.
From our limited trials with SynergEyes and from feedback gleaned from experienced fitters, it seems there's still a place for high Dk piggy-backing. Particularly for decentred cones, scarring, high spots, invagination, severe irregularity and astigmatism, which do not seem well suited to this generation of hybrid lens technology.

I thus cannot wait for the extended power range of TruEye as we generally prefer to use a low plus si-hy lens for piggybacking [due to its marginally steeper anterior surface]. I'm told I won?t have to wait much longer. A daily version would be ideal and some comments on the web seem to confirm this potential.

As with all new lenses I reserve judgment on SynergEyes and TruEye until I have some longer term results.
At any rate we welcome all useful additions to our contact lens armamentarium.

If we can enhance safety, comfort and vision and maintain long term corneal integrity then we have to be happy.

 

More Predictions?


As many of you noticed my Super 14 predictions were spot on as was my ?France by five? prediction texted to a mate at kickoff for the first test. As previously commented, I always wondered why the ABs retained their choker coach when he led what was supposed to be one of the most formidable teams ever, to an embarrassing loss at Cardiff in the 2008 RWC.
In South Africa they even fire winning coaches!
We lost a great coach to Aussie and NZ may well rue the day they let him go.
I would now upgrade my prediction that the Boks will prevail over the ABs [and likely Aussie too] but of course I may be wrong and there are still the Lions to contend with.

Button, Brawn and their great Mercedes motors continue to dominate F1.
Who would have thought?
The ski season?s also looking good.

If we survive swine flu, there's still much enjoyment to be had in life.

 

For more information or any comments email Alan at incontact@optom.co.nz.