A Case for Increased Oxygen and Reversal of Myopic Shift

Alan Paul Saks MCOptom (UK), DipOptom (SA), FAAO (USA), FCLS (NZ)

Alan Saks is a New Zealand Optometrist with extensive experience in speciality contact lens fitting, management and education. He completed a four-year diploma course in Optometry and a three year Dispensing diploma at Technicon Witwatersrand, Johannesburg, South Africa in 1981, and worked in South Africa before Immigrating to New Zealand in 1993.

He has contributed to a range of pharmacy and optometry based textbooks, newsletters and magazines, and has edited the 'In Contact' column for NZ Optics over the past eight years. He is a Fellow of the American Academy of Optometry and of the New Zealand Society of Contact Lens Practitioners; is a Past President (2001 and 2002) and current Council member of the New Zealand Society of Contact Lens Practitioners; and Past President of the Contact Lens Society of South Africa.

High Dk silicone hydrogel torics - in the form of PureVision Toric [PVT] and Acuvue Advance for Astigmatism [AAFA] – have opened up new options for the long-suffering corneas of soft toric wearers.

Here’s a case report that clearly illustrates a number of important issues.

It relates to a now presbyopic lady who, the record shows, has been wearing soft lenses for around twenty three years. Her prefit spectacle refraction was recorded as:

R-1.50/-0.75x160
L -1.50/-1.00x10

I noted that colleagues had unsuccessfully tried 1980s style EW, RGPs and in later years disposables. Colleagues had also tried Spectrum and CIBA Torisoft’s and recorded ‘miss-location’ as the reason for failure.  A pair of NuToric 38s were finally fitted with good stability and vision. At this stage she was already up to:

R -2.25/-1.25x170
L -2.00/-1.75x180

I first met this pleasant, motivated lady in 1997 when I took over her contact lens care. After discussing the issues I refitted higher water lenses and ordered her Rx in NuToric 55. Within days of dispensing these she developed ‘sore, red eyes’ and slit lamp revealed bilateral SEALs. I redesigned the lenses but these mislocated and in fact the left lens did a ‘one eighty’ and located with the scribe mark around 12 O’clock. I also fitted some NuToric 67s with similar problems. I have previously reported on issues with the 67% water material used by the manufacturer, mostly relating to SEALs. [In retrospect this article from my April 2000 In Contact column makes for interesting reading for a number of reasons!]

Part of her problems related to ‘dry eye’ with a rather low BUT. At this point she advised she was reverting to her tried and tested NuToric 38s.

Not one to give-up easily, nor let HEMA-EDEMA get the better of me, I ordered and trialed various lenses at each aftercare but alas none worked. These included, Omniflex and BENZ G5X custom torics, Acti-, XCEL, Biomedics, Proclear and SofLens66 disposable torics - all with a combination of problems mostly relating to dryness, discomfort, instability and breakages.

At each attempt I grudgingly ordered her a new pair of her trusty 38s or she reverted to her current lenses after an intensive in-office clean.

Believe me it wasn’t for a lack of trying and these attempts came at considerable cost to the patient, practice and suppliers.

She wouldn’t even consider giving RGPs another go. In October 2004, I was keen to fit her with PureVision Toric lenses as part of a pre-market trial we were performing.

Refraction in October 2004 was:

R -3.25/-2.00x12
L -2.00/-2.75x 176

This represented a significant further increase in myopia and astigmatism compared to her Rx of twenty years prior. Was this shift natural myopic progression or was it Soft Lens Induced Myopia [SLIM]? The fact that this was mostly SLIM - as a result of long term hypoxia - becomes very clear when you compare prefit K readings with those just prior to refitting the Purevision torics, as follows:

Prefit K:           R 42.75/44.37
Nov 2004 K:    R 43.62/45.75

Simple maths shows that this is around 1.00D steeper and thus largely responsible for the increase in myopia and astigmatism. The left eye was similarly affected.

Experience at altitude and over two decades has led me to expect around a 10% reduction in myopia when we provide the cornea with more oxygen but as predicted by the above K changes, this one regressed much more.

After just over 3 weeks in her first set of Purevision Torics she commented enthusiastically that the lenses were more comfortable than her trusty HEMA torics.

Yippee!

After eight years of battling I can tell you that this breakthrough was music to my ears. Her only complaint was that her ‘near vision’ had got progressively worse over the past weeks. That too was positive news as it was probably due to myopia reduction. This was confirmed by over-refraction of:

R +1.00
L +0.50

Almost what one may expect from the aforementioned K changes! The measured refractive error confirmed this:

R -2.00/-1.75x10
L -1.50/-1.75x180

On examination a year later (Nov. 2005) she mentioned mild lid/lens discomfort and I suspected this was most likely modulus related.  As Acuvue Advance for Astigmatism [AAFA] had recently become available in her Rx, I refitted her with these lenses.  They located pretty well with good stability and her K readings were now closer to prefit levels.

She is now wearing monovision to better manage her presbyopia - with her left non-dominant eye corrected for near. An email a few days later simply said “These lenses are very comfy”.

So, if you’ve been letting things ride with your low Dk disposable toric wearers there’s no longer an excuse to leave anyone in that obsolete technology. Most patients will not only succeed and benefit but will be much better off as far as long term corneal heath is concerned. You have to at least give them a try with the benefit of healthier, happier, whiter eyes.

Viva Oxygen.