Abstract
Corneal transplantation aims to replace opacified, scarred or deformed corneae with cadaveric donor material. However, there are two clinical scenarios when we need to consider bypassing the ocular surface and cornea with a keratoprosthesis to restore sight in corneal blindness. Where there have been multiple graft failures or a heavily vascularised cornea, and in the presence of adequate tear production and perfect blink mechanism, a Boston Type 1 keratoprosthesis (BKPro1) may be considered instead of high risk keratoplasty. BKPro1 is a PMMA and titanium collar stud device which sandwiches a carrier corneal graft button for full thickness transplantation. Limbal stem cell deficiency is not a problem but any degree of keratinisation, tarsal or bulbar, will compromise outcomes. Where the ocular surface is hostile with keratinisation, and in the presence of a defective lid or blink, an osteo-odonto-keratoprosthesis (OOKP) is indicated. Nothing else, such as keratoplasty, BKPro1, or limbal stem cell transplantation, will work. The OOKP is an epicorneal device using a lamina created from the patient’s own canine tooth root and surrounding jawbone to carry a PMMA optical cylinder, shrink wrapped by an overlying buccal mucous membrane graft. Keratoprostheses are inherently unstable and should not be used when there is a fellow seeing eye, and should not be implanted bilaterally.Twenty-seven publications by the author on keratoprostheses are reviewed. The gold standard known as the Rome-Vienna protocol is introduced following an extensive consensus meeting. The author's own results and those from other major centres where he taught the technique are reviewed. Complications such as laminar resorption and mucous membrane overgrowth are described in detail along with the author's attempt to enable early detection and surgical treatment. The author’s attempts to improve optical performance through iterations of optical cylinder design are also discussed. Where there is no tooth, the author’s approach to alternatives is discussed including how to choose the best alternative based on availability and evidence base. Development of a synthetic OOKP lamina is also discussed. The competitor device Boston KPro Type 2 is discussed and a new name for the device is suggested.
I recently gathered the outcomes of the OOKP cases whom I operated on during the period 1996- 2014. There were 25 females and 39 males, and in total, 65 eyes and 74 laminae were studied. The most common diagnosis was Stevens-Johnson syndrome (SJS; n=27, 43%) followed by cicatrising auto-immune conjunctivitis (n=19, 29%). In this cohort, 67% of laminae showed clinically detectable resorption. Overall autologous laminar retention was 91% over 18 years. However, 33% of the allografts survived over 5 years with prophylactic exchange. Six autografts, three allografts and one of the tibial grafts were prophylactically exchanged with new laminae.
Glaucoma was the most frequent complication in these eyes (n=57, 86%). It was noted in 26% (n=17) of the eyes before OOKP and in 60% after OOKP. Tube shunt devices such as the Ahmed valve and the Baerveldt tube implants were employed in 14 eyes. Thinning (n=22, 34%) and ulceration (n=8, 12%) were common mucosal complications (46%) after Stage 1. After Stage 2, mucosal overgrowth (n=21, 28%) was more common than mucosal ulceration (n=14, 19%). Retroprosthetic membrane (RPM) formation was detected in 13% of laminae. Endophthalmitis was the commonest cause of visual loss. Endophthalmitis occurred in 10 cases, three of which developed after intraocular surgical procedures (following Stage 2 in one case and after tube shunt implantations in 2 cases). In 7 cases, resorption was the main factor in inducing endophthalmitis.
Visual acuity prior to OOKP was hand movements (HM) to light perception (LP) in 51 (77%) eyes, counting fingers (CF) to less than 6/60 Snellen acuity in 6 eyes and 6/60 in one eye. Ten eyes (15%) did not experience significant improvement in vision. End-stage glaucoma was the most frequent cause of lack of visual improvement after OOKP surgery. Autografts showed a 61.7% functional survival probability of better than 6/12 visual acuity and a 68.8% probability of acuity between 6/12 and 6/60 over 13 years. Among the allografts, only two eyes retained a vision of 6/9 and 6/4 throughout the life of the lamina. Three allograft eyes were blinded due to endophthalmitis and one due to end-stage glaucoma.
| Date of Award | 2022 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Somnath Mukhopadhyay (Supervisor) & Andrew Lloyd (Supervisor) |