m
Recent Posts
Connect with:
Monday / March 4.
HomemifeatureSize Matters?

Size Matters?

One discussion that continues to rage is the ‘big’ versus ‘small’ RGP contact lens debate. Scleral lenses have, over the past few years, become rather trendy. But where in the patient mix do they best belong?

Certain practitioners seem to be infatuated with sclerals and very large intra-limbal lenses. I’ve had interesting deliberations with colleagues around the world on this topic for some time. I’m neither a scleral lens convert nor an expert and doubt I’ll ever become one. I have fitted them in the past – and, in fact, manufactured my own scleral lenses – right through from moulding the eye, casting a corneo-scleral replica in plaster-of-Paris, to pressing and finishing the final PMMA haptic lens.

Of course sclerals have evolved dramatically since then. High Dk gas permeable materials have at least made them viable options, as have modern four-axis CNC lathes and milling machines.

Keeping an open mind, I’ve investigated and fitted the odd ‘corneo-limbal’ Rose K XL lens in recent times, ably assisted by the legendary Paul Rose, for a few patients where all else had failed.

To me that is the niche that sclerals occupy – a last resort lens for extreme cases. There are, however, quite a number of practitioners that seem to think sclerals are the ‘go to’ lenses for all manner of cases. That I just don’t get: sclerals have a higher risk of metabolic and physiological complications, limited Dk/L, poor tear exchange, trapped metabolites, toxic reactions and a significant risk of seal off, blanching of limbal vessels, neovascularisation, potential limbal stem cell damage and tricky handling and maintenance.

To my mind they are often fitted ‘too tight’. The sometimes inexperienced practitioners are, however, apparently ‘happy’ because they obtain 20/20 vision with good centration and comfort. My biggest issue with this is that this short-term satisfaction will potentially lead to longer-term serious complications.

I see some very interesting case reports with some phantasmagorical lens designs on some pretty extreme eyes. That said I’ve also seen scleral lenses fitted on post-RK patients where they’ve caused significant neovascularisation; right into the pupil zone, along all the radial cuts. I’ve similarly seen such things develop in graft patients after a few months or years of scleral lens wear. To me that is not success and I believe these patients would have been better off with other contact lens options. In my experience high Dk piggybacks may be a successful alternative.

There’s enough in the literature to cover all this, with many frequent posts, articles and papers that cover both sides of the scleral lens debate, so enough said. However, what I will add is that, in the hands of experienced contact lens specialists, coupled with frequent and thorough aftercare, these lenses can be a breakthrough for long suffering patients.

We also know that corneal rigid gas permeable (RGP) lenses are unbeaten in safety and success, with many wearers attaining decades of fantastic results.

I’m thus pleased to see a number of gung-ho scleral fitters modifying their philosophy and fitting the smallest lens indicated, wherever possible. That’s not to say that these people are going extreme and fitting 8mm RGPs but certainly 9.6 to 11mm corneal RGPs seem quite small in comparison to sclerals!
Most of the RGPs I’ve fitted over the past four decades have ranged between 8.4 and 9.8mm. There have been a few 7.2–8.2mm and 10–11.2 mm lenses but these are mostly for extreme cases.

I’ll occasionally fit super-small lenses on some grafts, or those with peripheral corneal scarring, dryness, dellen and pterygia; where the lens edge would otherwise traumatise these raised areas of corneal tissue with resultant irritation, inflammation, neovascularisation, infiltrates and the potential for abrasion and infection. Conversely I may fit super-large corneal lenses for post-RK, post-LASIK ectasia, off-centre cones, an occasional complicated graft and so on.

I would, however, generally forsake RGPs in such cases and fit toric or spherical high Dk si-hy lenses, wherever possible and whenever decent vision can be obtained. The benefit of high Dk si-hy soft lenses is that they do not pose any significant physiological compromise, while usually providing high levels of comfort and in many cases, excellent vision. They also offer the benefits of ‘bandaging’ any peripheral scarring, pterygia and desiccated areas, thus offering added benefits. I‘ve had many successes managing such cases since the advent of si-hy lenses 18 years ago. A few such case reports are still floating around the Internet, as are a few piggyback cases.

A Case in Point

Allow me to share a corneal RGP case that had some interesting aspects.

A young lady from Canada had recently moved to NZ. She’d been wearing some Canadian made corneal RGPs for her extreme hyperopia, associated with microphthalmos, with satisfactory results for many years. She’d broken her right contact lens and been seen numerous times by a local chain. They had made four lenses over the past six months and had also asked the local RGP lab to help sort it out. The patient was becoming quite frustrated and was suffering from discomfort and visual problems. She was referred by a patient and former optical/contact lens industry colleague, who had simply told her “Go see Alan, he’ll sort you out”.

She said the NZ lenses all felt too big and too loose with excessive movement and inferior decentration. She is right eye dominant with mild amblyopia in the left and her ocular Rx is around +15.00D OU. She said all of the right eye replacement lenses were unacceptable and uncomfortable: she could not see well at work and night vision was similarly poor. She was developing marked asthenopia after just three hours of computer work and her eyes were sore at the end of the day, with headaches.

I found she was taking +1.50D over her most recent NZ RE RGP lens, which I measured at 6.81mm BC, 9.7mm diameter and a power of +14.25D.

I also analysed her left lens and as a short-term solution, gave her the old satisfactory left lens to wear in her dominant right eye to tide her over while I urgently ordered a custom SAKS design, multi-curve, lenticulated RGP lens. As I was leaving for a lecture tour a few days later, I arranged for my experienced colleague and contact lens lecturer to check on it while I was away.

The lens I designed and had made was as follows;

6.74wet (8.2)7.20(8.6)8.10(9.0)10.00 with an overall diameter of 9.5 and power of +16.37D.

It was made in Boston XO, with a custom lenticular, -14.00D carrier, LZ of 8.4mm and DAC blending of 0.3 on the back surface and 0.2 on the lenticular junction, with the thinnest centre thickness possible for the design/power.

On returning from my travels I asked my colleague, who is a hard task master, if the lens had performed okay. He said it was fantastic! The patient was rapt and he told me to look at his clinical notes. He’d written “amazing fit, centres well, adequate edge lift. Patient is overjoyed and will return to refit her other eye”.

Boom!

Alan P Saks MCOptom(UK) Dip.Optom(ZA) FCLS(NZ) FAAO(USA) is a third generation optometrist based in Auckland, New Zealand and columnist for mivision. He is actively involved in the profession, having served multiple terms as president of Contact Lens Societies and arranged numerous conferences. He has also served on education committees, as examiner in contact lenses and clinical optometry examinations, lectured contact lenses to ophthalmology registrars and written several columns about eye health and the practice of optometry.