I was somewhat surprised by a recent post on a specialist scleral contact lens Facebook forum, where an OD (American optometrist) asked whether it was possible to fit a corneal rigid gas permeable (RGP) contact lens on an aphakic eye with a penetrating keratoplasty (PKP). Their concern was that the scleral lens design software had indicated a very thick scleral lens, related to a very high plus power. They were correctly considering a better option.

It was pleasing to see that this question didn’t arise from one of our southern hemisphere colleagues. But my concern was that someone with over a decade in practice was unaware that this kind of condition has been successfully fitted with RGPs for more than 50 years. In fact, some aphakes were even fitted with zero Dk PMMA (Polymethyl methacrylate) corneal lenses and thick, low Dk HEMA (2-hydroxyl-ethyl methacrylate) soft lenses. Often with great success.

Several forum members from Australia and around the world supportively commented that of course it’s possible, and in fact a better, safer option than a scleral lens. We collectively provided helpful information. That’s one of the positive things about educational forums, which are generally free of the vitriol, negativity, and criticism that we all too often see on social media.

As I’ve often stated, my concern with the rapid swing to scleral lenses is that due to their initial good comfort, centration, and vision, other options like corneal RGPs, soft lenses, and piggyback systems are overlooked. We have always had optometrists in every generation and region that lacked adequate skills and training in the nuances of corneal RGPs. One young optometrist, however, observed that corneal RGPs had quietly slipped out of routine training for many newer practitioners, and the learning curve to fit them comfortably, safely, and with good centration is not a small one.

HELP IS AT HAND

As many experts attest, it’s often best to avoid scleral lenses in PKP and aphakes. As one very experienced world leader in contact lenses stated, “I recently saw a 50-year-old graft wearing a (corneal) RGP lens. He asked about sclerals, and I advised against (since he wasn’t having any trouble). Corneal RGP lenses are very healthy for grafts – less inflammatory.”

Lenticular designs reduce thickness, lens volume/mass and shift the centre of gravity further back to counter gravitational effects, which aids centration. Smaller lenses that leave more exposed cornea can also be beneficial to maximise available atmospheric oxygen and reduce potential hypoxia, resultant oedema, and potential neovascularisation into the graft tissue. One of the reasons corneal grafts were the first successful human transplants – going back over 100 years – is the relative avascularity of the cornea, which provides an immune privilege. The last thing we want to do is have blood vessels approaching or penetrating the graft-host junction, increasing the risk of inflammation and graft rejection.

Another thing that younger practitioners may not have been taught or be aware of, is that a cornea of an aphakic eye has a reduced corneal oxygen demand versus a phakic eye.1 This was shown by researchers including our very own Brien Holden, Debbie Sweeney, and others, and detailed by Desmond Fonn2 – one of my colleagues, lecturers and mentors – who also spent time at the Cornea and Contact Lens Research Unit (CCLRU) in Sydney with the aforementioned, among other legends. Key findings were that epithelial oxygen uptake was significantly lower in aphakic corneas as was hypoxic swelling response. They concluded that the aphakic cornea has a lower metabolic oxygen demand than the phakic cornea. This knowledge is beneficial in contact lens fitting.

Although there may still be challenges in fitting what seems like a complex grafted cornea, a corneal RGP fitted by an expert would likely be the best option. Avoiding oedema, preventing dimple veiling, minimising any insult to the cornea – particularly at the site of raised, graft suture scars, and so on – are key factors to success. A lens of around 9.2 mm diameter with a lenticular design, and where needed, toric back surface/toric periphery or a reverse geometry/quadrantic design, will potentially all add to a decent safe fit and centration.

EDGY A decent edge profile is also a key to success. Poorly designed edges are a common, yet often overlooked, cause of lens discomfort.

In my experience – and that of colleagues with corneal lens experience going back to the 1950s – a well-tapered, relatively ‘sharp’ edge is the key. An over-rolled edge, with a profile that resembles the edge of a door, is not going to be well tolerated by an eyelid bumping over it 14,000 times a day. Never mind potential damage to sensitive glands, the lid wiper, and so on, as this can lead to long-term tear film and ocular surface disorders.

WRAPPING IT UP

In summary, the case from our American colleague would be best referred to an expert rather than attempted as a first-time fit on such a complex cornea. Ideally, the referring practitioner would sit in on the appointment and use it as an opportunity to build the design skills they’ll need down the track.

The Cornea and Contact Lens Society of Australia (CCLSA), offers both formal and informal mentoring. Help is just a click away. And don’t forget to register for the International Cornea and Contact Lens Congress (ICCLC) in Hobart during October. It’s a highlight of the CPD calendar with great collegiality and is full of useful learning on ocular surface, contact lenses, myopia, and much more.

Feeling disillusioned or burnt out? Come along and reignite the passion for optometry, dry eye, and contact lenses that ICCLC and CCLSA are famously known for sparking.

See you there!

Alan Saks is a retired optometrist. He is the Chief Executive Officer of the Cornea and Contact Lens Society of Australia, and a regular contributor to mivision.

References available at mivision.com.au.