Modified Osteo-odonto Keratoprosthesis
In eyes with advanced ocular surface disease, the only hope for restoration of visual function is the use of prosthetic devices. The modified osteo-odonto keratoprosthesis (MOOKP) technique uses a composite bone-tooth lamina to help anchor a polymethyl methacrylate cylinder to the cornea. Originally pioneered by Prof Strampelli, it has evolved to its present form due to the interest and expertise of Prof Giancarlo Falcinelli from Italy.
The complex surgical procedure is performed in two stages. In the first stage, a canine tooth is harvested from the mouth of the patient after X-ray screening has determined that the tooth has a healthy and viable root structure. A surgical motorized saw is used to excise the canine root encased in alveolar bone from the jaw. The lamina is fashioned by sawing through the root of the tooth in a longitudinal fashion to expose the dentine and the root canal. The pulp in the root canal is scraped off and a hole is drilled in the widest part of the root - to a size of 3 to 4 mm depending on the width of the root at that point. An appropriate sized plastic cylinder of appropriate power (determined from the axial length of the eye to be operated) is then glued to the hole using dental cement. A subcutaneous pocket is created in the tissues of the cheek and the lamina-cylinder complex is placed and the pocket is sutured closed after installing antibiotic powder. In the eye, the symblephara are released, and scar tissue is excised as described earlier. A superficial keratectomy including the Bowman's layer is performed to expose the bare corneal stroma after which a full-thickness circular piece of cheek mucosa about 4 mm in diameter is placed over the cornea and sutured to sclera, also covering the muscle insertions.
Stage II is performed 2 to 3 months later to allow time for a connective tissue cover to develop around the lamina implanted in the cheek. If required the integrity of the lamina can be checked by performing a spiral computed tomographic evaluation. During the second stage surgery, the lamina is retrieved from the subcutaneous location and excess connective tissue is removed from the two ends of the optic cylinder, and trimmed over the rest of the lamina. The mucosal graft on the ocular surface is incised superiorly and reflected from the superior sclera and cornea, in a downward direction. The inferior attachment of the mucosal graft is left undisturbed to ensure that the blood supply is retained.
A Flieringa ring is sutured in place and a 3mm opening is created in the center of the cornea. Three radial incisions are made in the cornea extending till the limbus. The iris is torn at the root and removed and hypotensive anesthesia is used to control the ooze. Constant irrigation with balanced salt solution also helps wash the blood away and prevents a large clot from forming in the anterior chamber. The lens is then cryoextracted and the corneal radial cuts are sutured closed. A limited anterior vitrectomy is performed and the lamina is then placed over the cornea, such that the posterior part of the optic cylinder is in the anterior chamber - entering through the central corneal opening. The lamina is sutured into position using the connective tissue covering and episcleral bites. At the conclusion of suturing, indirect ophthalmoscopy is performed to ensure that there is a good view of the disc and posterior pole. If this is not seen, a cylinder tilt may be responsible and sutures need to be adjusted to straighten the cylinder. Any bleeding into the vitreous cavity can also interfere with the visualization. After the cylinder and lamina are in satisfactory position, the mucosal flap is replaced and a small opening is created over the optic cylinder to allow the anterior portion of the cylinder to protrude through the mucosa. The superior edge of the mucosal flap is sutured in place and this completes the operation.
Although the procedure is complex and involves time, energy and effort from surgeons dealing with multiple specialties, it offers desperate patients hope for sight. It is however, not a simple procedure, and the complexity of the surgery requires meticulous attention to detail, asepsis and technique. The procedure does provide useful functional vision to the patient, although the field of vision tends to be limited.