Royal College of Ophthalmologists Guidelines

Modern osteo-odonto-keratoprosthesis (OOKP) surgery

Cadaveric corneal transplantation is generally successful for reversing corneal blindness. There are, however, some patients who are not amenable to such transplantation. They typically have severely dry eyes and the only procedure that may work is keratoprosthesis. Strampelli described the original technique of osteo-odonto-keratoprosthesis (OOKP) surgery nearly forty years ago, using the patient's own tooth root and alveolar bone as vital support to an optical cylinder ¹. Early British followers of his technique reported poor retention results ². Falcinelli modified the technique in a stepwise fashion ^3-6 and the improved technique was re-introduced into Britain, at our hospital, 1996 ⁷. The Falcinelli OOKP, where adequately performed, is now recognised internationally to give the best long term visual and retention results amongst all keratoprosthesis, especially in a dry eye.

Referral guidelines

Patients with bilateral corneal blindness resulting from severe Stevens-Johnson syndrome, ocular cicatricial pemphigoid, chemical burns, trachoma, dry eyes or multiple corneal graft failure may be considered. The better, or only, eye should have poor vision such as PL, HM or at best CF. One eye only will be rehabilitated. In suitable cases, there would be no need to go through unsuccessful penetrating keratoplasty with or without limbal stem cells transplantation and amniotic membrane grafting beforehand. Previous history of retinal disesase, glaucoma and other optic nerve disease, ocular perforation, as well as pre-phthisis may compromise outcome.

The OOKP assessment clinic

This joint clinic is run by an ophthalmologist (CL) and a maxillo-facial surgeon (JH). Pre-operative assessment includes ascertaining an intact and functioning retina and optic nerve by relatively accurate projection of light in quadrants, a normal B-scan (also for axial length), and in selected cases flash ERG and VEP. Following oral examination and radiography, a choice is made as to which tooth (usually a canine) to harvest depending on the length and girth of the root, the state of surrounding alveolar bone, and the amount of gum recession. In the absence of a suitable single-rooted tooth, the use of an HLA-matched relative's tooth is possible, but prolonged immunosuppression with cyclosporine will be necessary. The patient and their relatives are counselled regarding the complexity of surgery, success rates, possible complications and their management (see Table 1) and that they should consider the procedure as irreversible. A new optical cylinder we developed is shorter and wider than the original Italian design providing a much wider but still restricted field of view (circa 100 degree), which has been found to be beneficial in patients with age related macular degeration ⁸.

Surgical technique

OOKP surgery is performed usually in two stages spaced two to four months apart. The gap allows soft tissue to grow around the osteo-odonto lamina and for ocular surface reconstruction with buccal mucous membrane grafting to become vascularised.

 

Table 1: Potential complications of OOKP surgery
Eye
Buccal mucous ulceration in the early post operative period (especially in smokers)
Lid malposition and loss of fornix
Secondary glaucoma	(10.4%)
Tilting of optical cylinder	(rare)
Extrusion of keratoprosthesis	(rare)
Retroprosthetic membrane formation	(rare)
Retinal detachment	(rare)
Endophthalmitis	(rare)
Mouth
Poor mouth opening
Damage to adjacent tooth
Oro-antral fistula	(rare)
Jaw fracture	(rare)
Systemic
Complications of cyclosporine treatment	(rare)

Each stage takes approximately six hours and special anaesthetic precautions are necessary ⁹. Prior to OOKP surgery, it is important to treat pre-existing glaucoma by cyclodestruction. Fornix reconstruction, where necessary, can be carried out beforehand or at the time of stage 1 procedure.

Stage 1 involves ocular surface reconstruction and fashioning of an osteo-odonto lamina and its optical cylinder. A large circular piece of buccal mucosa is harvested from the cheek. The graft is trimmed of excess fat and soaked in cefuroxime solution. A lateral canthotomy is performed, followed by division of symblephara and superficial keratectomy. The buccal mucous membrane graft is sutured to the sclera bounded by the insertion of the rectus muscles to create a new ocular surface. The crown of the harvested tooth is used as a handle; whilst the attached tooth root and surrounding bone is worked into a lamina with dentine on one side and bone on the other. Periosteum is conserved and where possible glued back with fibrinogen adhesive. A hole is drilled through the dentine to accommodate a PMMA optical cylinder, which is cemented in place. The resultant osteo-odonto lamina is placed into a sub-muscular pocket under orbicularis oculi, usually in the lower lid of the fellow eye, in order to acquire a soft tissue covering.

Stage 2 starts with retrieval of the osteo-odonto lamina from its sub-muscular pocket and excess soft tissue is removed from the bone surface. On the dentine surface, no soft tissue is allowed to remain. The lamina is reinserted into its pocket until the eye is ready to receive it. The buccal mucosal graft is reflected to allow access to the cornea. A Flieringa ring is sutured in place. The centre of the cornea is marked, and a small hole is trephined, the diameter of which corresponds to that of posterior part of the optical cylinder. Relieving incisions are made and total iridodialysis, lens extraction and anterior vitrectomy are performed. The posterior part of the lamina is inserted through the central corneal hole and the lamina is sutured onto the cornea and sclera. The eye is re-inflated with filtered air. The mucosal flap is replaced after cutting a hole to allow the protrusion of the anterior part of the optical cylinder (Figures 1 and 2) ¹⁰.

Results

Falcinelli reported excellent long term retention results (85% in 18 years) with 75% of patients seeing 6/12 or better ¹⁰. In our unit, 9 out of 15 cases (60%) have a post operative vision of greater or equal to 6/24 and in 7 out of 15 cases (46.66%) post operative vision was greater or equal to 6/12. Eighty percent of patients achieved improvement of vision. In general, patients with compromised visual outcome have had pre-existing optic nerve and retinal comorbidity.

Conclusions

OOKP surgery is complex and requires meticulous care at each step to ensure the overall success rate. Therefore, surgeons must not attempt to provide a service without first having undergone adequate training. Oral structures have to be sacrificed. All patients experience glare and a restricted visual field. The cost of OOKP surgery to the NHS is in the region of eight to ten thousand pounds and formal cost benefit analysis has confirmed its cost effectiveness (unpublished data). Although it is far from perfect, modern OOKP surgery is the only hope for restoring sight in the long term for desperate cases of corneal blindness not amenable to conventional corneal surgery.

Christopher Liu, Padmanabha Pillai Syam, Jim Herold and Simon Thorp, Sussex Eye Hospital, Brighton. Correspondence: CSCLiu@aol.com

References

1 Strampelli, B. Keratoprosthesis with osteodontal tissue. AM J Ophthalmol 1963; 89: 1029-1039.

2 Casey, TA. Osteo-odontocheratoprotesi and chondrokeratoprosthesis. Proc Royal Soc Med 1970; 63: 313-314.

3 Falcinelli GC, Barogi, G, Corazza E, Colliardo P. Osteo-odonto-cheratoprotesi: 10 anni di esperienze positive ed innovazioni. Atti LXXIII Congresso Soc. Oftalmologica Italiana, 1993, 529-532.

4 Falcinelli G, Missiroli A, Petitti V, Pinna C. Osteo Odonto Keratoprosthesis up to Date. Acta XXV Concilium Ophthalmologicum 1986. Rome. Kugler & Ghedini; 1987: 2772-2776.

5 Falcinelli G, Barogi G, Taloni M. Osteoodontokeratoprosthesis: present experience and future prospects. Refract Corneal Surg 1993; 9: 193-194.

6 Falcinelli G, Barogi G, Caselli M, Colliardod P, Taloni M. personal changes and innovations in Strampelli's osteo-odonto-keratoprosthesis. An Inst Barraquet (Barc) 1999; 29(S)47-48.

7 Liu C, Herold J, Sciscio A, Smith G, Hull C. osteo-odonto-keratoprosthesis surgery. Br J Ophthalmol 1999; 83(1):127.

8 Hull C, Liu C, Sciscio A, Eleftheriadia H, Herold J. Optical cylinder designs to increase the field of vision in the osteo-odonto-keratoprosthesis Graefe's Archive for Clinical and Experimental Opthalmology 2000; 238: 1002-1008.

9 Skelton VA, Henderson K, Liu C. Anaesthetic implications of osteo-odonto-keratoprosthesis surgery. European Journal of Anaesthesiology 2000; 17: 390-394.

10 Liu C, Sciscio A, Smith G, Pagliarini S, Herold J. Indications and technique of modern osteo-odonto-keratoprosthesis (OOKP) surgery. Eye News. 1998;5:17-22.