MODIFIED OSTEO-ODONTO-KERATOPROSTHESIS

Some keratoprosthesis surgeons consider the modified osteo-odonto-keratoprosthesis (mOOKP) an option for visual rehabilitation in only the most challenging KPro candidates – those with extremely dry eyes and the worst ocular surface disease. However, for Konrad Hille MD, the mOOKP is the procedure of choice as long as the patient has a suitable tooth for fabricating the device.

Speaking at the 2nd EuCornea Congress, Dr Hille defended what he acknowledged was likely a provocative viewpoint by presenting outcomes from his personal series of 33 patients. Noting that he was assigned to speak about “Demystification of the OOKPâ€, Dr Hille said he was perplexed at first by this title and uncertain about what should be the content of his talk.

Superior device

“I see nothing mystifying about the OOKP. The procedure can be performed successfully by a skilled surgeon, anatomical success data from Falcinelli show it is superior to other keratoprostheses with survival in some cases reaching nearly 30 years, and patients who undergo the procedure unanimously agree that it was worth exchanging a tooth for an eye,†he noted. Dr Hille also noted the result of Falcinelli’s Kaplan-Meier curve with anatomical success of about 90 per cent over 20 years (88 per cent).

“Perhaps the best way to demystify the procedure is to show how it works in my hands,†said Dr Hille, Josephs-Hospital Eye Department at Ortenauklinikum, Offenburg, Germany.

His series of 33 patients had a median age of 53 years (range, 18 to 70) and median follow-up of eight years (range to 15 years). Nearly half had severe dry eye, most often associated with pemphigoid, and preoperative visual acuity was less than 0.05 in the better eye.

Visual acuity improved to 0.9 or better in 10 (31 per cent) eyes. While it remained 0.05 or less in 13 per cent of eyes, the latter cases were patients with poor visual potential secondary to retinal or optic disc disease. There were some patients who had loss of visual acuity over time. These events were due to diabetes in two eyes, and glaucoma in two eyes. There were two cases of anatomic loss, one due to an iatrogenic surgical error, and the other after development of a corneal melt.

Complications included mucosal necrosis (42 per cent) and bone absorption (six per cent). There was a relatively low rate of retroprosthetic membranes (six per cent).

Discussing OOKP complications, Fook Chang Lam MD, reviewed findings of research being conducted at the Sussex Eye Hospital, National OOKP Referral Centre, Brighton, UK, that are providing insights on laminar resorption/extrusion and glaucoma. He reported highlights from histological studies performed in 12 specimens, including eight laminae from cases of OOKP reversal or replacement, two specimens from eviscerated eyes, and two from whole donor eyes of patients who died with functioning OOKPs.

Dr Lam noted the histological observations confirm previous information about the role of chronic inflammation in laminar resorption. Interestingly, however, in one of the functional OOKPs obtained after the patient’s death, the alveolar dental ligament was intact, but there were subepithelial colonies of bacteria and yeast-like organisms accompanied by chronic inflammation. Evidence of bone remodelling and bone reformation was also found despite absence of damage to the alveolar dental ligament.

Other findings from the histological evaluations have relevance to the development of glaucoma. Despite total iridodialysis, iris remnants in one eye had led to formation of peripheral anterior synechiae that closed off the trabecular meshwork. In another eye with an intact alveolar-dental ligament, there was stratified squamous epithelium lining the corneal defect, Descemet’s membrane, ciliary body and angle, leading to trabecular meshwork collapse. Evidence of chronic inflammation and giant cell formation as a reaction to absorbable sutures was also present in this patient who was apparently well.

Discussing clinical management of OOKP complications, Dr Lam reported on the introduction of multi-detector CT with volumetric analysis for evaluating laminar resorption. “This technology allows us for the first time to reproducibly and accurately measure laminar volume in vivo and compare serial scans to detect thinning. We believe it has important applications clinically and for research,†he said, illustrating its clinical use with the case of a patient who was shown to achieve stabilisation of laminar volume loss after starting treatment with a bisphosphonate.

Major challenge

Dr Lam also reviewed outcomes in a consecutive series of 48 patients followed for six months to 13 years to highlight that management of glaucoma continues to be a major challenge in OOKP patients. In this cohort, glaucoma was present prior to OOKP surgery in 27 per cent of eyes and at last follow-up in 52 per cent. Due to poor ocular penetration of topical medications, all of the patients were on oral medications for IOP-lowering, predominantly acetazolamide SR. Ten patients had undergone cyclodiode or endocyclodiode laser treatment intra- or postoperatively, and more recently rectus disinsertion and reinsertion surgery has been attempted, noted Dr Lam.

“Most patients still require tube surgery for management of progressive glaucoma, but results with tube surgery have been discouraging.â€

Of five patients who had tube surgery, one had spontaneous tube extrusion, one developed endophthalmitis after orbital cellulitis, and the tube was rendered nonfunctional in two patients as the pseudocapsule around the plate blocked aqueous flow.

“In the future we will probably place tubes at an earlier stage or even preplace them at the time of the OOKP surgery. We are considering endoscopic vitrectomy to improve the success of tube surgery and reduce the likelihood of retinal detachment in the future. However, there are other risks to consider with use of this approach,†Dr Lam said.