Keywords: Keratoprosthesis; alveolar bone; PMMA optic; vascularisation
Osteo-Odonto-Keratoprosthesis (OOKP) is a preferred technique of vision restoration surgery in eyes with end stage ocular surface disorders such as Steven-Johnson syndrome, ocular circatricial pemphigoid and dry keratinized eyes following severe chemical burns. The conventional corneal transplant surgery has much poorer prognosis in these disorders due to intense vascularisation of cornea. OOKP uses an acrylic optical cylinder which replaces the diseased cornea and gives excellent image resolution and quality. Although the possibility of immune mediated rejections is less than conventional grafts, the technique is associated with inherent complications such as resorption of bone lamina which can lead to extrusion of the graft and retroprosthetic membrane formation. This makes the technique not only surgically difficult but also demands long term follow-up of the patient. In spite of this being a tedious procedure, it definitely has promising visual outcomes. .
Introduction scan of canines was carried out for selection of a suitable Osteo-Odonto-Keratoprosthesis (OOKP) is a vision resto- tooth with the assistance of an oro-maxillofacial surgeon. ring surgical technique where the patient's opaque cornea Surgical technique is replaced with artificial optical device. This optical devi- Stage 1 involves ocular surface reconstruction and fashioce is made up of a PMMA (polymethylmethacrylate) cylin- ning of an osteo-odonto lamina and its optical cylinder (Fider which acts as an artificial cornea. Thus, the device is ca- gure 1). A large circular piece of buccal mucosa is harveslled keratoprosthesis (kerato means cornea and prosthesis ted from the cheek. The graft is trimmed off excess fat and means artificial device). This PMMA cylinder is embedded soaked in cefuroxime solution. A lateral canthotomy is perin a base made from patient's own tooth which is then sutu- formed, followed by division of symblephara and superficred to the cornea to restore the vision. The procedure is do- ial keratectomy. The buccal mucous membrane graft is sutne in patients with end stage corneal disease where conven- ured to the sclera bounded by the insertion of the four recttional corneal graft has a poor prognosis. The conventional us muscles to create a new ocular surface (Figure 2). surgery includes the use of a full thickness corneal button Harvesting the tooth excised from a cadaver eye (allograft), which replaces the The ideal tooth with the best surrounding bone is usually diseased cornea of partial or total opacity. When it is assoc- the canine tooth. Other single-rooted teeth can be used in iated with intense vascularisation, it prevents the taking up the absence of a canine. The assessment of suitability of the of the donor graft and leads to graft rejection. Thus, these tooth can be done by clinical examination but depends maipatients are eligible for keratoprosthesis. A vast number of nly on radiological assessment. The mainstay views are ordesigns and materials of keratoprostheses have been devel- thopantomograms (OPG) and intra-oral periapical radiogroped and implanted in the patients. The technique with the aphs (IOPAs). The choice of upper or lower canine depends best results and long term follow-up is the osteo-odonto- on the proximity of the maxillary sinus in the upper and the keratoprosthesis (OOKP) invented by Strampelli and mod- proximity of the mental foramen in the lower. The lower 1 canine harvesting is straightforward but the buccal plate is ified over the years by Prof. G Falcinelli. This technique occasionally a little thin and the lingual muco-periosteum demands the involvement of both dental and ophthalmic is more difficult to preserve. The upper canine occasionally surgeons to complete the procedure. Thus, it is necessary gives too much bone palatally and there is a risk of violat-for both the surgeons to understand the finer details of the ion of the antrum. procedure and its possible complications which can be avThe harvest of the osteo-odontal lamina involves the secti-oided with adequate precautions during the surgery and tioning of bone on either sides and apical to the chosen tooth mely follow-up of the patients. and removing the tooth and its surrounding alveolar bone, together with the associated mucoperiosteum (Figure 3). Case report The incision is made to the bone and mucoperiosteum elev-A 56-year-old man reported to an eye hospital for restoraated from the adjacent teeth. The bone cuts are made betw-tion of vision. A detailed history to determine the primary een the teeth and below the chosen tooth with a fine saw. diagnosis and previous surgical interventions was recordThe resulting alveolar defect is covered as best as possible ed. A brisk perception of light and normal B-scan was an with adjacent mucosa but the exposed bone reepithelialises essential pre-requisite. Intraocular pressure was usually asvery rapidly.sessed by digital tonometry. Oral assessment included assThe crown of the harvested tooth is used as a handle; whilst essment of oral and dental hygiene and state of buccal muthe attached tooth root and the surrounding bone is worked cosa. An orthopantomography (OPG), X-ray and spiral CT into a lamina with dentine on one side and bone on the ot- infection. After the lamina is retrieved from its sub-muscuher. Periosteum is conserved and wherever possible glued lar pocket, the soft tissue is excised (Figure 5) and a temback with fibrinogen adhesive. A hole is drilled through the plate is made of the lamina in order to plan placement of dentine to accommodate a PMMA optical cylinder, which prosthesis. The buccal mucosal graft is reflected to allow is cemented in place (Figure 4). The resultant osteo-dental access to the cornea. The centre of the cornea is marked, acrylic lamina (ODAL) is placed into a sub-muscular poc- and a small hole is drilled, the diameter of which correspket under orbicularis oculi, usually in the lower lid of the onds to that of the posterior part of the optical cylinder. Refellow eye, in order to acquire a soft tissue covering. lieving incisions are made and total iridodialysis, lens extStage 2 starts with retrieval of the osteo-dental acrylic lam- raction and anterior vitrectomy are performed. This is necina (ODAL) from its sub-muscular pocket (Figure 1). It is essary otherwise the iris tissue gets plastered on the postecarried out 2 to 4 months after Stage I for the soft tissue to rior surface of the optical cylinder. The posterior part of the invest into the bone pores of the lamina. The interval also lamina is inserted through the central corneal hole and the allows the lamina to recover from thermal damage and any lamina is sutured onto the cornea and sclera (Figure 6).eye is re-inflated with filtered air. The mucosal flap is repl- of rejection of a penetrating graft due to highly vascular coaced after making a hole to allow the protrusion of the ant- rnea. It is also done in patients with severe grade chemical 2 or thermal injury to the cornea which leads to total corneal erior part of the optical cylinder. opacity, keratinisation of cornea, conjunctival ischemia and dry eye. Other indications include repeated failed pen-Discussion etrating keratoplasties where there is little corneal tissue le-OOKP is a surgical technique where the patient's own tooft for subsequent graft. The conventional graft is more like-th is used to form a biological frame to support an acrylic ly to fail when it is larger in size (a large diameter graft will optic cylinder. This surgery restores the sight of patients be nearer to the corneo-sclera junction and the blood vesse-with end-stage ocular surface disease where conventional ls, thus at risk of immune mediated reaction). In patients grafts fail because of intense vascularisation and subsequewith aniridia there is congenital limbal (corneo sclera junc-nt graft rejection or dessication. In diseases with severe oction) stem cell deficiency along with the absence of iris ti-ular surface inflammation and dry eyes, this technique has ssue. Limbal stem cells are multipotent cells which help in been found to be more successful than other purely syntheepithelialisation of the grafted cornea after the transplant. tic prostheses. OOKP provides a stable and superior long Loss of these cells will lead to rejection in cadaver grafts term visual rehabilitation in these patients. but not in artificial prosthesis. Thus, OOKP is indicated for Indications and contraindications vision restoration in such patients.The procedure is indicated in bilateral cases of Cicatricial Rare indications include case with severe corneal opacity corneal diseases such as Stevens Johnson syndrome and resulting from complicated ocular surgical procedures su-Ocular cicatricial pemphigoid where there is high chance ch as vitrectomy with silicone oil injection and cataract ex- been done to assess the success of the procedure, and visual traction with vitreous touch to corneal endothelium. In th- status many years after surgery has been found to be norm7 ese procedures corneal endothelium is decreased in numbal. The vision in these patients is likely to decrease over a er and unable to maintain the transparency of cornea. longer period of time due to antecedent complications such The only absolute contraindications to the procedure are as glaucomatous optic nerve damage, laminal resorption absent light perception and an edentulous patient. Posterior and retroprosthetic membrane formation. Thus, more studsegment of the eye (retina and optic pathway) should be no- ies are needed to assess the long term visual outcome in thrmal before carrying out the surgery. Thus, irreparable reti- ese patients and the development of possible late post-openal detachment or other posterior segment pathologies su- rative complications. ch as macular degenerations are contraindications for this 3procedure.
Hille K, Grabner G, Liu C, Colliardo P, Falcinelli G, Taloni Complications M, et al. Standards for modified osteoodontokeratoprosthes-Oral complications of OOKP surgery may include excessis (OOKP) surgery according to Strampelli and Falcinelli: ive scarring of the buccal mucosa, exposure of roots of the the Rome-Vienna Protocol. Cornea 2005;24:895-908.adjacent teeth, damage to maxillary sinus and parotid duct 2. Liu C, Sciscio A, Smith G, Pagliarini S, Herold J. Indications which may occur while extracting the tooth and the alveoand technique of modern osteo-odonto-keratoprosthesis (O lar bone. OKP) surgery. Eye News 1998;5:17-22.-Ocular complications during Stage I surgery include the ri 3. Falcinelli G, Falsini B, Taloni M, Colliardo P, Falcinelli G. sk of globe perforation, post-operative lamina and mucous Modified osteo-odontokeratoprosthesis for treatment of cor4 neal blindness: long-term anatomical and functional outco-membrane infection, and laminal resorption. During Stage mes in 181 cases. Arch Ophthalmol 2005;123:1319-29.II surgery there may be a risk of vitreous hemorrhage, chor4. Stoiber J, Forstner R, Csaky D, Ruckhofer J, Grabner G. Ev-oidal or retinal detachment. aluation of bone reduction in osteo-odontokeratoprosthesis Late postoperatively, there may be diminution of vision (OOKP) by 3-dimensional computed tomography. Cornea due to retroprosthetic membrane formation and subseque2003;22:126-30.nt rise in intraocular pressure. This may lead to glaucomat- 5. Falcinelli GC, Falsini B, Taloni M, Piccardi M, Falcinelli G. 5 ous optic nerve damage and irreversible visual loss. There Detection of glaucomatous damage in patients with osteoodcan be resorption of the bone lamina leading to extrusion of ontokeratoprosthesis. Br J Ophthalmol 1995;79:129 -34. 6 6. Stoiber J, Csaky D, Schedle A, Ruckhofer J, Grabner G. His-the optical cylinder. topathologic findings in ex-planted osteoodontokeratopros-Though an extremely demanding and time consuming prothesis. Cornea 2002;21:400-4.cedure, the rewards can be extremely satisfying if the adeq7. Liu C, Okera S, Tandon R, Herold J, Hull C, Thorp S.. Visual uate precautions are observed by both the dental and ophthrehabilitation in end-stage inflammatory ocular surface dis-almic surgeons. Although the technique was described soease with the osteoodonto-keratoprosthesis: results from the me 40 years ago, subsequent improvements in the methodUK. Br J Ophthalmol 2008;92:1211-17