|Year : 2020 | Volume
| Issue : 3 | Page : 159-166
Osteo-odonto keratoprosthesis in Egypt: a case series
Mohamed B Goweida
Department of Ophthalmology, Alexandria Main University Hospital; Department of Ophthalmology, Faculty of Medicine, Alexandria University, Alexandria, Egypt
|Date of Submission||02-Jan-2020|
|Date of Decision||18-Mar-2020|
|Date of Acceptance||24-Mar-2020|
|Date of Web Publication||23-Sep-2020|
FRCOphth, FRCS(Glasg), PhD Mohamed B Goweida
9 Hussein Hassab Street, Bab Sharki, Alexandria 21131
Source of Support: None, Conflict of Interest: None
Purpose The aim of this study was to evaluate the preliminary results of osteo-odonto keratoprosthesis (OOKP) performed in Alexandria Main University Hospital, Alexandria, Egypt in eyes with end-stage cicatrizing conjunctivitis.
Patients and methods OOKP surgery was done in two stages. Stage 1 included preparation of the globe, buccal mucous membrane harvesting, and preparation of osteo-odonto alveolar lamina with the cemented optical cylinder. The prepared lamina was then placed in the submuscular space for 2–3 months. In stage 2, the lamina–optical cylinder complex was implanted under the buccal mucous membrane and the posterior part of the optical cylinder was placed in a central corneal opening to act as an artificial cornea, transmitting image to the retina.
Results Six eyes with end-stage ocular surface disease were included in this study. Anatomical success, in the form of retention of the prosthesis, was achieved in five eyes. The procedure failed in one eye due to unhealthy canines with a small amount of bone in the lamina. Functional success, defined as restoration of vision, was achieved in four eyes. Visual improvement was not attained in one eye (in addition to the eye with anatomical failure) due to optic atrophy despite good retention of the device.
Conclusion OOKP is a promising procedure to regain vision in severe cases of end-stage corneal blindness, unsuitable for cadaveric corneal grafts. Proper selection of cases is crucial to achieve the best anatomical and functional results.
Keywords: cicatrizing conjunctivitis, keratinized ocular surface, keratoprosthesis, osteo-odonto
|How to cite this article:|
Goweida MB. Osteo-odonto keratoprosthesis in Egypt: a case series. Delta J Ophthalmol 2020;21:159-66
| Introduction|| |
Osteo-odonto keratoprosthesis (OOKP), a technique invented by Strampelli  and modified over the years by Falcinelli et al. ,, is considered the most successful technique for visual rehabilitation in bilateral end-stage ocular surface disorders. OOKP has proved to afford the best long-term retention among other keratoprosthesis procedure, especially in the dry keratinized ocular surface ,.
The basic principle of OOKP surgery is fashioning a plate formed of a single rooted tooth with its surrounding bone, to be used as a carrier for an optical cylinder that acts as an artificial cornea, transmitting images to the retina. This complex is sutured to the sclera and the posterior part of the optical cylinder is fitted through an opening in the opaque cornea. Stabilization of the complex is carried out with the aid of the covering buccal mucosal membrane (BMM) graft. The dental lamina allows for long-term stability and fixation of the optical cylinder, while the BMM prevents tissue breakdown and melting around the device ,,,.
In Egypt, there is a large number of patients with treatable corneal blindness. Chemical injuries are quite common due to both assaults and industrial injuries. Cicatrizing conjunctivitis, in the form of mucous membrane pemphigoid or Stevens–Johnson syndrome, are relatively underestimated and patients do not receive the necessary immunosuppressive treatment. These diseases can eventually lead to a dry keratinized ocular surface with absent blink mechanism and consequently other types of keratoprosthesis such as Boston type 1 will not be suitable as a treatment option .
With the increasing number of patients with end-stage ocular surface disorders in Egypt, the OOKP service was initiated in Alexandria, Egypt in June 2015. In this article we describe our experience of six OOKP surgeries done in our tertiary referral center.
| Patients and methods|| |
This study was conducted in accordance with the tenets of the Declaration of Helsinki and was approved by the Institutional Ethics Committee of the Faculty of Medicine, Alexandria University. All operations were performed at Alexandria Main University Hospital, Alexandria, Egypt from June 2015 to October 2019. OOKP surgeries were done in all cases using the Rome-Vienna Protocol and following its guidelines . All patients signed a written informed consent to participate in the study and for publication of data before enrollment into the study.
Patients with bilateral blindness due to end-stage cicatrizing conjunctivitis, chemical burn, or severe dry eye were enrolled into the study. Both eyes were required to have poor vision that was not better than counting fingers and not worse than perception of light. One eye was operated upon and the other eye was left as a reserve for future rehabilitation, if unmanageable complications happened in the operated eye. Patients were required to have healthy BMM and good canines without caries or bone resorption.
Exclusion criteria included the following:
- Patients who were happy with their level of vision.
- Unilateral corneal blindness.
- Children under the age of 18 years.
- Eyes with evidence of phthisis, advanced glaucoma, or retinal detachment.
- Patients with no light perception, bad mouth hygiene, scarred BMM, unhealthy teeth, or edentulous patients.
Clinical examination included confirmation of at least light perception vision and slit-lamp evaluation of the anterior segment if possible. B-scan ultrasonography was performed to assess the posterior segment and to perform axial length measurement. Ultrasound biomicroscopy was done if the details of the anterior segment could not be examined by the slit lamp. Flash electroretinogram and visual-evoked potential were needed in some cases to confirm a functioning retina and optic nerve.
Oral examination was performed by the dental surgeon to evaluate the canines and mucosal health. Mandibular radiograph and cone beam computed tomography were performed to choose the suitable canine.
The procedure was explained in detail to all patients, including the prolonged staged nature of the procedure, the possible need for further surgical interventions, the risk of serious complications including loss of eye, bad cosmetic appearance of the eye following surgery, and the need to commit to lifelong follow-up visits.
The OOKP procedure was performed in two or three stages. Stage 1 could be divided into 1a and 1b according to surgeon’s preference:
Stage 1a: preparation of the globe and BMM harvesting ([Figure 1]), where the keratinized ocular surface was dissected to expose the cornea, sclera, and the four rectus muscles ([Figure 1]a). The harvested BMM was then sutured to the sclera and the insertion of the recti to create a new ocular surface ([Figure 1]b and c).
|Figure 1 Preparation of the ocular surface in stage 1 osteo-odonto keratoprosthesis (OOKP): (a) removal of keratinized ocular surface and exposure of the cornea, sclera, and the four rectus muscles, (b) suturing of the buccal mucous membrane (BMM) graft to the sclera and the insertion of the rectus muscles, (c) complete covering of the ocular surface with BMM graft.|
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Stage 1b: preparation of the osteo-odonto alveolar lamina, where the canine and the surrounding bone was harvested and fashioned into a lamina with dentine on one side and bone on the other side. An optical cylinder was then cemented in the lamina after drilling a hole in the center of the dentine, with dimensions allowing the cylinder to snugly fit in it. The lamina with the cemented optical cylinder was then placed into the submuscular space, under the orbicularis oculi of the contralateral eye.
Stage 2: implanting the lamina under the BMM ([Figure 2]), 2–3 months following stage 1. The lamina was retrieved from the submuscular pocket and all soft tissue was removed from the dentine surface. The BMM covering the ocular surface was incised superiorly ([Figure 2]a) and dissected from the sclera and cornea, leaving the inferior attachment undisturbed to retain its vascular supply ([Figure 2]b). A 5 mm corneal trephination was then done, followed by total iridodialysis, intracapsular lens extraction, and anterior vitrectomy ([Figure 2]c and d). The posterior part of the optical cylinder (dentine side) was then inserted into the 5 mm corneal opening ([Figure 2]e) and fixed by suturing the soft tissue overlying the bone side of the lamina to the sclera. Repositioning and suturing of the BMM flap was then done, after the creation of a central hole, to allow protrusion of the anterior part of the optical cylinder ([Figure 2]f).
|Figure 2 Stage 2 OOKP: (a) incising the superior part of the BMM, (b) dissection of the BMM from the ocular surface, sparing the inferior part, (c) trephining the cornea and avulsion of the atrophic iris, (d) anterior vitrectomy after intracapsular lens extraction. (e) placement of the lamina so that the posterior part of the optical cylinder (dentine side) fits in the 5 mm corneal aperture, (f) the reflected BMM is replaced, sutured, and a hole is created to fit the anterior part of the optical cylinder. BMM, buccal mucous membrane; OOKP, osteo-odonto keratoprosthesis.|
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It included measurement of best-corrected visual acuity, intraocular pressure measurement digitally, looking for any signs of bone resorption such as focal laminar thinning or mobile optical cylinder, and optic disc and retinal evaluation.
| Results|| |
Six eyes with bilateral end-stage ocular surface disorder were included in the study ([Table 1]).
|Table 1 Age, sex, diagnosis, and outcome of osteo-odonto keratoprosthesis|
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A 67-year-old-female patient presented in June 2015 with bilateral end-stage cicatrizing conjunctivitis and keratinized ocular surface. Stage 1 OOKP was done, but was complicated with breaking of the only healthy canine during harvesting. So, the procedure was completed using one of the upper incisors. BMM was harvested and sutured to the ocular surface. However, a central hematoma appeared in the postoperative period, which progressed to necrosis and infection ([Figure 3]a, b and c), necessitating excision of the central area and repair using labial mucous membrane and sliding flap ([Figure 3]d, e and f). At 3 months later uneventful stage 2 was performed. After 4 years of follow-up, the best-corrected visual acuity was 0.4 and the cup disc ratio was 0.8.
|Figure 3 Case 1: (a) central hematoma in the BMM, (b) central infected area, (c) progression to the necrotic area, (d) intraoperative excision of the necrotic area, (e) covering of the bare area with sliding BMM flap from the superior part, and (f) labial mucous membrane covering the bare superior area. BMM, buccal mucous membrane.|
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A 63-year-old-male patient presented with Sjogren’s syndrome and previous failed corneal grafting in both eyes. Visual acuity in one eye was no light perception and in the fellow eye was hand movement with dry ocular surface and total symblepharon. Intraocular pressure was controlled on topical antiglaucoma medications. Uneventful stages 1 and 2 were done on September 2015. One month following surgery, a small area of bone exposure appeared through the BMM and reintervention using sliding flap was done after grinding of the exposed bone spicule ([Figure 4]a and b). Four years after surgery visual acuity was 0.3 with progressive optic disc damage and cup disc ratio of 0.9. To date, the patient is refusing any further intervention.
|Figure 4 Case 2: (a) small area of bone exposure, (b) after grinding of the protruded bone and covering the bone by the sliding BMM flap. BMM, buccal mucous membrane.|
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An 80-year-old male patient with end-stage cicatrizing conjunctivitis, total ankyloblepharon, history of glaucoma, previous cataract surgery, and failed corneal graft, presented with a PL vision with normal B-scan ultrasonography and good electrophysiological studies of the optic disc. Despite a successful stages 1 and 2 surgeries and good anatomical retention 3 years postoperatively, visual acuity did not improve after surgery due to optic nerve atrophy.
This was a 65-year-old-female patient with end-stage cicatrizing conjunctivitis and total symblepharon. Stage 1 was complicated by necrosis and thinning of the BMM, necessitating a sliding labial mucous membrane for reconstruction of the necrotic area. Stage 2 was done, and vision improved to 0.4. However after 6 months, a large area of bone exposure appeared, with unstable optical cylinder and hypotony ([Figure 5]a). Owing to the unhealthiness of the BMM and previous complication in stage 1, the decision was to cover the whole area with the lids and to perform a total tarsorrhaphy, leaving the optical cylinder protruding through the skin ([Figure 5]b). Vision improved to 0.2 and is stable till the present time.
|Figure 5 Case 4: (a) large area of bone exposure, (b) after total tarsorrhaphy and through the lid keratoprosthesis.|
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This was a 69-year-old-female diabetic patient with end-stage cicatrizing conjunctivitis, total ankyloblepharon, and total cataract. Stage 1 was complicated by thinning and necrosis of part of the BMM that required a repair similar to case 4. The canines were in a bad condition, with gum recession and bone resorption. The best canine was chosen by the maxillofacial surgeon and stage 1 was completed. On retrieving the buried canine after 3 months, a small amount of soft tissue was formed around the bone. Stage 2 was completed, but on the second day the optical cylinder–bone complex was mobile and unstable. Revision of surgery revealed cheese-wiring of all sutures due to the poor amount of soft tissue. So, removal of the optical cylinder–bone complex was done and a tectonic graft was sutured.
This was a 25-year-old-male patient with a history of chemical burn, multiple surgeries in the form of amniotic membrane transplantation, multiple patch grafts, and tectonic keratoplasty. Examination showed totally opaque vascularized cornea, symblepharon, and absent blink mechanism. Uneventful stages 1 and 2 were done, with good anatomical and functional outcome. Visual acuity was 0.4 after 6 months.
| Discussion|| |
Several keratoprosthesis (kpro) devices have been described to restore vision for patients with end-stage ocular surface diseases, in whom conventional corneal surgery is expected to fail. Boston kpro type 1 is the most widely used device and is composed of two plates, sandwiching a donor corneal button, with the stem of the front plate passing through a hole in the donor graft. The donor cornea is sutured to the recipient cornea. Since a donor corneal graft is used in Boston type 1 kpro, it is only suitable for wet blinking eyes ,,.
In eyes with a dry keratinized surface and absent lid mechanism, a modification to Boston kpro, the so-called type 2 kpro, was designed to allow implantation through the surgically closed eyelids by means of an anterior extension . Owing to poor long-term retention of Boston kpro type 2, artificial implants with biological skirts remain the mainstay of treatment for eyes with dry keratinized ocular surface. OOKP has shown the best long-term results compared with other suggested biological skirts such as the cartilage and the tibial bone ,,,. The long-term success of OOKP is explained by the presence of dentine, which is the second hardest tissue in the body and is avascular with a slow metabolic exchange rate. Thus, the dentine provides a good support to the fixed optical cylinder and prevents retroprosthetic membrane formation . Moreover, the interconnected pore spaces of the bone provide fixation and vascularity of the supporting tissue . The BMM is a physiological covering, having a proliferating capability, resistant to high bacterial load and provides blood supply to the bony part of the lamina .
This case series represents one of the several reports describing the outcome of OOKP. The largest case series was published by Falcinelli et al. , who performed 181 patients with more than 90% anatomical survival and 70% visual survival after 9 years. Liu et al.  reported 56 and 44% anatomical and visual survival, respectively, after 9 years of follow up of 35 patients. Iyer et al. , in their case series of 50 patients, achieved 95% anatomical success and 66% visual success after 15 months of follow-up. Tan et al.  reported 100% anatomical success and 73% functional success in 15 patients after a mean of 19 months of follow-up.
In this case series, two patients had poor results following surgery. One patient had light perception vision and good electrophysiological studies preoperatively, but no visual improvement occurred despite good anatomical success. Although, the Rome-Vienna Protocol recommended a minimum vision of light perception , it is better to select patients with hand motion vision in the early cases. The other patient had poor oral condition and long-standing diabetes mellitus, which may be a contributing factor to this failure. The amount of bone surrounding the dentine is an important factor for the success of the procedure, as bone provides long-term stability of the lamina and ensures good surrounding soft tissue for suturing of the lamina to the sclera. The paucity of bone around the canines resulted in failure of the procedure both anatomically and functionally. Although many of these patients are eager to restore vision, proper selection of cases is crucial before initiating the OOKP procedure, to avoid disappointing results to the patient and the surgeon.
Glaucoma is considered a common complication after kpro in general. In this cohort of patients, one patient had preexisting glaucoma and another patient developed de-novo glaucoma. Fundus examination and visual field testing are the available means to diagnose and monitor glaucoma after surgery. Topical antiglaucoma medications cannot penetrate the BMM, so systemic acetazolamide, despite its side effects, is the only effective medication after OOKP. Tubes can be implanted in eyes with progressive glaucoma, but failure of drainage may occur due to encapsulation of the plate under the BMM or obliteration of the episcleral drainage by the BMM. It is advisable to treat glaucoma preoperatively by cyclodestructive procedures prior to initiation of the OOKP procedure ,.
BMM complications were very common in this case series necessitating reintervention in four cases. This was attributed to poor mouth hygiene in most cases, uncontrolled diabetes in cases 1 and 5, rough bony part eroding the BMM in case 2 and unexplained necrosis of the covering BMM in case 4. Three of these cases were corrected by sliding the BMM flap with covering of the peripheral defect with labial mucous membrane. Case 4 was not amenable to repair due to large area of bone exposure, which was corrected by surgical closure of the lids over the lamina. Mucosal complications of OOKP in the form of thinning, ulceration, necrosis, and laminar exposure were discussed by Avadhanam et al.  in a case series of 64 eyes and were found to affect 46% after stage 1 and 22% after stage 2.
The limitations of this study are the small number of cases and the short follow-up period of some cases, which is due to the novelty of the technique in Egypt. In addition, the absence of financial support by insurance and the psychological influence of patients and families toward this lengthy unfamiliar procedure are other limitations. Nevertheless, this case series provides preliminary results of the first six OOKP patients done in Egypt and the results are considered encouraging to use OOKP as a solution for the large number of patients with corneal blindness who are not suitable candidates for the traditional cadaveric corneal grafts.
| Conclusion|| |
In conclusion, OOKP surgery appears to be a promising procedure to regain vision in severe cases of end-stage corneal blindness, unsuitable for cadaveric corneal grafts. Longer follow-up of these cases is underway.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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