Overcoming Corneal Blindness: Australian Keratoprosthesis Service

The AKS was established at Sydney Eye Hospital and Save Sight Institute in 2014 by Drs Greg Moloney (cornea and oculoplastics specialist, Sydney), Colin Clement (glaucoma subspecialist, Sydney), Mark Gorbatov (retinal subspecialist, Sydney), and Shannon Webber (oral maxillofacial surgeon, Gold Coast).

This highly specialised ophthalmic clinic cares for people who are bilaterally vision impaired from devastating corneal blindness…

This highly specialised ophthalmic clinic cares for people who are bilaterally vision impaired from devastating corneal blindness, where normal corneal transplantation techniques are highly likely to fail.

With the support of the Sydney Eye Hospital Foundation and its donors, the service has grown in strength to manage this unique subset of patients from all over Australia and New Zealand.

To restore sight in these patients, the AKS service performs one of two highly specialised procedures, Boston keratoprosthesis (Type 1) and the modified osteo-odonto keratoprosthesis (m-OOKP).

Prior to the AKS’s establishment, the Boston Keratoprosthesis device had not been implanted in Australia and patients in need of m-OOKP were required to travel to Singapore, the closest centre offering this service. This limited accessibility to only those who could afford to travel and invited higher risk for complication management, with time delays due to travel potentially worsening outcomes.

In the early days of its establishment, the AKS team was exceptionally fortunate to receive training and supervision from Dr Konrad Hille of Dusseldorf, Germany, a world-class pioneer in this highly specialised area of surgery. We would like to honour and thank Dr Hille who gave so generously of his time to share his expertise.

The Service Today

Currently, the ASK comprises a highly resourced, multi-disciplinary, centralised referral centre for Australia with a clear and structured referral pathway. With charitable funding from the Sydney Eye Hospital Foundation and the public system, patients from all over Australia and New Zealand can access its service for free.

Current members of the Service include:
• Dr Tanya Trinh (cornea, external diseases, and refractive surgeon),
• Dr Colin Clement (glaucoma surgeon),
• Dr Mark Gorbatov (vitreo-retinal surgeon),
• Dr Shannon Webber (maxillofacial surgeon), and
• Dr Greg Moloney maintains an annual visit to continue the osteo-odonto keratoprosthesis service, in addition to regular consultation.

The AKS sees patients on a once monthly basis at Sydney Eye Hospital with the joint involvement of Drs Trinh, Clement, and Gorbatov, and the Fellows of each department respectively.

Dr Peter Martin, orbit and oculoplastics surgeon, is also a significant and highly valued contributor to the management of many of the complex cases seen at the ASK.

Boston Keratoprosthesis

The Boston keratoprosthesis (Boston Kpro) is one of the most widely used artificial corneas in today’s anterior segment reconstructive domain, with more than 5,000 devices now implanted worldwide.

Invented by Professor Claes Dohlman, the Boston Kpro received United States Food and Drug Administration (FDA) approval in 1992. The device essentially consists of three components – an anterior plate with a central optical stem, a backplate of titanium, and a titanium locking C ring. The latter holds the device assembly in one piece with the donor cornea sandwiched in between.

Since its invention, the Boston Kpro has undergone several iterations in design, including:
• The addition of holes in its backplate to enhance the diffusion of nutritive aqueous that supports the maintenance of the donor graft stroma and keratocytes,
• The addition of a titanium ring locking device to enhance intraocular stability, and
• A threadless assembly design to prevent damage to the donor endothelium.

To reduce the frustration of retroprosthetic membrane formation and stromal corneal melts, a titanium backplate was added to improve biocompatibility and retention.

Ideal Boston Keratoprosthesis Candidate

The indications for the Boston KPro include patients suffering from bilateral corneal blindness with wet, blinking eyes, typically from entities such as:
• Multiple transplant failures,
• Limbal stem cell deficiency, or
• Select cases of Aniridia.

It should be noted that a higher incidence of repair, and worse final visual outcomes, are significantly higher in candidates with underlying autoimmune conditions. This appears to be related to the overall degree and cumulative extent of inflammation.

Risks Of a Boston Keratoprosthesis

It is important to know that despite the significant improvement that this device makes to the quality of the life of people with bilateral corneal blindness, it is not a device without its own challenges.

There are significant risks of glaucoma, device extrusion, and subsequent endophthalmitis with the Boston Kpro. Therefore, the decision to undertake such a procedure requires careful counselling and assessment of the patient (and their carer or support network), in terms of their ability to comply with close monitoring, and frequent, multidisciplinary long-term follow-up.

Without this, devastating complications can arise that can result in a substantial decrease in vision or at worst, loss of the eye. For this reason, candidates are generally only considered when they have bilateral corneal blindness where the benefits outweigh the risks.

A number of initiatives are adopted to prolong the retention of this device, including long-term, large-diameter, extended contact lens wear and daily lifetime topical antibiotic prophylaxis. Despite this however, patients are often counselled that ‘a good run’ means three to five years of ‘borrowed time’ or meaningful sight, according to the literature. Despite the significant work required to retain these devices in the human eye, we believe the improvement in the quality of life for these patients is undeniable and worth pursuing. The first Boston Kpro implanted in the AKS program will celebrate its 10th year in 2024.

Modified Osteo-Odonto-keratoprosthesis

For the bilaterally blind cases where the ocular surface is unable to sustain a Boston Kpro – as generally a moist surface with good lid function is required – the m-OOKP is the procedure of choice.

The m-OOKP involves the use of a single rooted canine tooth and surrounding intact alveolar bone to fashion a plate upon which a polymethyl-methacrylate cylinder is mounted. It is generally used for patients with bilateral corneal blindness with a dry, keratinised surface and poor lid closure or function. Where there is no suitable dental tissue other sites, such as calvarium, pelvis or tibial bone, may be selected as suitable donor sites.

Ideal M-Ookp Candidate

Ideal candidates for referral for m-OOKP consideration are patients:
• Who are bilaterally blind from corneal or ocular surface blindness (acuity < 1/120 in the better eye),
• With vascularised, dry, keratinised corneas with profound limbal stem cell failure, and/or
• With severe lid trauma or lid tissue loss.

Again, the ability to attend the AKS clinic on a very regular basis with support persons is of paramount importance.

The general conditions that would be serviced by the m-OOKP would include Stevens-Johnson syndrome, ocular cicatricial or mucus membrane pemphigoid, chemical/thermal burns, or severe lid involvement from resection or cicatrising processes where maintenance of the ocular surface moisture is heavily impacted or lagophthalmos is present.

Poor candidates include paediatric cases, eyes that see no light perception, or eyes with retinal detachment or severe posterior pathology, people with unstable psychiatric status or inability to attend very regular follow-up in clinic. Some patients may not accept the cosmetic appearance of this device, or may be unwilling to donate a tooth.

Implantation Of The M-Ookp

Referrers and patients should be aware that the implantation of such a device requires a multi-stage operative procedure, where the optic is first formed from tooth or bone and allowed to vascularise. After three to four months, it is harvested and implanted onto the ocular surface with a covering of buccal membrane. Often, preparatory lid procedures are undertaken prior to the fashioning of the optic.

Risks With An M-Ookp

Glaucoma remains one of the most common causes of visual loss in m-OOKP, with an incidence of 36% at 10 years in the largest published series.¹ It often is either pre-existing or arises de novo. Medication delivery remains a challenge due to impaired topical absorption and the reliance on oral acetazolamide plays a key role in maintaining lower pressures. Intraocular pressure and progression monitoring also pose their own unique challenges, as visual fields are usually unreliable. For this reason, structural tests are the mainstay of monitoring. Tube placement is possible at the primary stage or at a later date, with cut down of the buccal mucosal graft overlying the prosthesis.

From a vitreo-retinal perspective, we require all our patients to undertake a diagnostic endoscopic vitrectomy (even for the Boston Kpro) to ascertain who may be the best candidates for either the Kpro or m-OOKP procedures. A formal vitrectomy allows for direct visualisation of the structural integrity of the optic disc, macula, and peripheral retina. It also enables a posterior vitreous detachment to be safely induced, which clears the vitreous for future procedures such as pars plana tube placement and permits early or prophylactic management of any pre-existing retinal tears or detachments. Overall, retinal detachment risk is approximately 5% in this patient group.

Onwards and Upwards

The AKS continues to contribute to pushing medical and surgical frontiers in this area, publishing on a temporo-parietal flap incorporation in the m-OOKP to achieve further longevity of the dental lamina and pioneering the use of the inferior orbicularis to repair m-OOKP peri-optic melt. Additionally, the incorporation of various technologies such as the MicroRec Beamsplitter and Adapter Camera enabled the AKS to perform Australia’s first internationally collaborative (Australia-Canada) live surgery between Drs Trinh and Martin (Sydney) and Dr Moloney (Vancouver). Dr Moloney continues to visit Australia to offer the OOKP service with Dr Trinh.

But as always, the experiences of patients – like Heather Pozzobon, over the page, – are where the real story lies.

How To Get in Contact with The Aks

Potential candidates for this service can be referred to the program co-ordinators Eleena Tran at [email protected] or Johnathan Nguyen at [email protected].

A summary of the patient’s ocular and medical history, as well as their support networks (carers who are able to attend their visits) and the involvement of local treating specialists, will help identify patients who are (or are not) clinically suitable, and who are able to maintain the level of commitment required for the upkeep of both of these devices.

As a minimum, in the stable and healthy state, the Boston KPro and m-OOKP require a visit to the clinic every three months for monitoring. Additionally, an annual computed tomography of the orbits is required of the m-OOKP candidates to monitor for bone resorption, which can be clinically undetectable.

Upon receipt of the referral, Dr Trinh will liaise with the referring clinician regarding the potential for some of the investigatory workup to be performed locally, prior to the patient and carer visiting Sydney Eye Hospital.

Not Much to Lose, Everything to Gain

In 2017, Heather Pozzobon saw her two sons – the youngest, by then 17 years old, for the first time ever. The oldest for the first time since he’d turned one. He was 22. Blind for 21 years, Ms Pozzobon had been diagnosed with Stevens-Johnson Syndrome at 32 and tragically, was diagnosed as being legally blind one year later. Despite this, through the cutting-edge technology she was able to access from The AKS at Sydney Eye Hospital, she was able to continue to enjoy her active outdoor lifestyle with assistance, including skiing with her young sons. “My sons were a great help to me. Although I tried not to depend on them as kids – I didn’t want to do that – they would always drop everything and help me if I asked them. I feel their experience growing up with me, and in a school with hearing impaired children, has shaped them as young adults. They are amazing.” Ms Pozzobon and her husband adopted a 16-year-old boy who grew up with their sons. “He moved in, followed my rules, developed the same level of empathy, and is now a scientist. I am immensely proud of them all.” Jumping Through Hoops When a family friend sent her an article about the osteo-odonto-keratoprosthesis procedure, she had no hesitation in contacting her optometrist, Jenny Sorregan. She “jumped through the hoops” and with the help of ophthalmologist Dr Colin Clement, Ms Pozzobon was referred to Dr Greg Moloney at Sydney Eye Hospital. By the time pre-testing for the surgery was completed, Ms Pozzobon had just 5% vision remaining in both eyes. When asked about whether she felt anxious about a “risky” surgery that involved implanting her own canine tooth into her cheek, Ms Pozzobon said “I didn’t have much to lose”. “Everything was getting really hard, and they told me that without surgery I would soon have to give up my independence,” she explained. New-Found Vision Post-surgery, it took five weeks for Ms Pozzobon’s sight to be restored. Initially she had double vision. Then, quite rapidly, she could see again. When she saw her sons and husband she said, “I didn’t cry – I’d cried so many times before – I was just so excited.” Although Ms Pozzobon has no peripheral vision, she has the vision she needs to navigate independently, to read without glasses and to see colours. She is even a bowling champion at her local bowls club. “I didn’t realise how many shades of green there are in the grass, until my sight was restored,” she said. She has also been able to get back to skiing and watersports under “strict rules”. “I’m not allowed to ride on a rollercoaster, but I am allowed to do other things, as long as I do them safely… When I ski, I follow a person, I stick to the blue, groomed runs, and am very aware of the people around me.” Ms Pozzobon’s vision has been stable for five years, although there has been a need for revisions of the operation to ensure she is able to maintain the level of vision and independence she has enjoyed since 2017. Heather is part of a small unique community of people who have had or are about to have the m-OOKP procedure. “We are like a little family. We catch up for lunch and talk about our experiences. I’m very exciting for the next three patients who are about to have the procedure. I hope they have the same experience as I have had,” she said. The m-OOKP is known to be one of the most stable forms of vision restoration surgery for corneal blindness. The Australian keratoprosthesis program relies on the surgical team who donate their time and the incredible generosity of the donors who support the Sydney Eye Hospital Foundation.