Abstract

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. OOKPuses 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

Keywords: Keratoprosthesis; alveolar bone; PMMAoptic; vascularisation

Introduction

Osteo-Odonto-Keratoprosthesis (OOKP) is a vision resto- ring surgical technique where the patient's opaque cornea is replaced with artificial optical device. This optical devi- ce is made up of a PMMA (polymethylmethacrylate) cylin- der which acts as an artificial cornea. Thus, the device is ca- lled keratoprosthesis (kerato means cornea and prosthesis means artificial device). This PMMA cylinder is embedded in a base made from patient's own tooth which is then sutu- red to the cornea to restore the vision. The procedure is do- ne in patients with end stage corneal disease where conven- tional corneal graft has a poor prognosis. The conventional surgery includes the use of a full thickness corneal button excised from a cadaver eye (allograft), which replaces the diseased cornea of partial or total opacity. When it is assoc- iated with intense vascularisation, it prevents the taking up of the donor graft and leads to graft rejection. Thus, these patients are eligible for keratoprosthesis. A vast number of designs and materials of keratoprostheses have been devel- oped and implanted in the patients. The technique with the best results and long term follow-up is the osteo-odonto- keratoprosthesis (OOKP) invented by Strampelli and mod- ified over the years by Prof. G Falcinelli.1 This technique demands the involvement of both dental and ophthalmic surgeons to complete the procedure. Thus, it is necessary for both the surgeons to understand the finer details of the procedure and its possible complications which can be av- oided with adequate precautions during the surgery and ti- mely follow-up of the patients.

Case report

A 56-year-old man reported to an eye hospital for restora- tion of vision. A detailed history to determine the primary diagnosis and previous surgical interventions was record- ed. A brisk perception of light and normal B-scan was an essential pre-requisite. Intraocular pressure was usually as- sessed by digital tonometry. Oral assessment included ass- essment of oral and dental hygiene and state of buccal mu- cosa. An orthopantomography (OPG), X-ray and spiral CT scan of canines was carried out for selection of a suitable tooth with the assistance of an oro-maxillofacial surgeon.

Surgical technique

Stage 1 involves ocular surface reconstruction and fashio- ning of an osteo-odonto lamina and its optical cylinder (Fi- gure 1). A large circular piece of buccal mucosa is harves- ted from the cheek. The graft is trimmed off excess fat and soaked in cefuroxime solution. A lateral canthotomy is per- formed, followed by division of symblephara and superfic- ial keratectomy. The buccal mucous membrane graft is sut- ured to the sclera bounded by the insertion of the four rect- us muscles to create a new ocular surface (Figure 2).

Harvesting the tooth

The ideal tooth with the best surrounding bone is usually the canine tooth. Other single-rooted teeth can be used in the absence of a canine. The assessment of suitability of the tooth can be done by clinical examination but depends mai- nly on radiological assessment. The mainstay views are or- thopantomograms (OPG) and intra-oral periapical radiogr- aphs (IOPAs). The choice of upper or lower canine depends on the proximity of the maxillary sinus in the upper and the proximity of the mental foramen in the lower. The lower canine harvesting is straightforward but the buccal plate is occasionally a little thin and the lingual muco-periosteum is more difficult to preserve. The upper canine occasionally gives too much bone palatally and there is a risk of violat- ion of the antrum.The harvest of the osteo-odontal lamina involves the secti- oning of bone on either sides and apical to the chosen tooth and removing the tooth and its surrounding alveolar bone, together with the associated mucoperiosteum (Figure 3). The incision is made to the bone and mucoperiosteum elev- ated from the adjacent teeth. The bone cuts are made betw- een the teeth and below the chosen tooth with a fine saw. The resulting alveolar defect is covered as best as possible with adjacent mucosa but the exposed bone reepithelialises very rapidly.