Outcomes of the Boston keratoprosthesis in jordan.

PURPOSE: To report the indications, outcomes, and complications of the Boston type I keratoprosthesis (KPro) from the first Jordanian study on the subject.
MATERIALS AND METHODS: A retrospective chart review was conducted on 20 eyes of 19 consecutive patients who had Boston type I KPro implantation at King Abdullah University Hospital. Surgeries were performed by the same surgeon (WS) from November 2007 to March 2010. Data collected included age, sex, primary indication, number of previous grafts, preoperative comorbidities, visual acuity before and after surgery, and complications.
RESULTS: The mean age of the participants was 51.7±19.9 years (range: 10-80 years). The mean follow-up was 18.1±9.5 months (range: 3-6 months). The most common primary corneal pathology was vascularized corneal opacity (40%). Best corrected visual acuity (BCVA) improved significantly in 85% of eyes; 65% had a BCVA of 20/200 or better and 25% had a BCVA of 20/50 or better. The most frequent complication was retroprosthesis membrane (RPM) formation, which occurred in 45% of eyes. Two eyes (10%) had implant extrusion and required further surgery.
CONCLUSION: Boston Kpro offers a reasonably safe and effective solution for patients with corneal blindness in whom the prognosis for natural corneal grafting is poor.

INTRODUCTION

Penetrating keratoplasty (PK) is the standard treatment for most corneal diseases that require surgical management.1 In low-risk clinical situations, PK is one of the most successful transplantations, with a 10-year success rate of 72%–80%.2–4 Certain conditions, however, including recurrent graft failure,5 congenital corneal opacities,6 aniridia, limbal stem cell deficiency,78 herpes zoster,910 ocular cicatricial pemphigoid (OCP), Stevens-Johnson syndrome (SJS),11 and ocular burns1213 have a poor prognosis with standard PK. The risk of graft rejection and failure increases with each failed corneal transplant.14 In other words, the outcome of keratoplasty varies markedly with the underlying disease, availability and quality of donor tissue, number of previous grafts, and other undetermined factors. This uncertainty led to decades of effort to develop a modern keratoprosthesis (KPro) to treat patients with corneal blindness and poor prognosis for PK. A variety of KPro have been designed, with varying success rates. One of the most commonly used devices in the United States is the Boston type I KPro.15 Outcomes of the first series of patients who underwent Boston type I KPro were reported in 1974, and the device was eventually approved by the FDA (Food and Drug Administration) in 1992.1617

The Boston KPro provides a clear visual axis without astigmatism and with rapid visual recovery postoperatively.18 It consists of polymethyl methacrylate optic (front) and back plates, with donor corneal tissue clamped in between. A recent modification to the design has incorporated 16 fenestrations in the back plate to improve nutrition to the donor corneal tissue. Also, the new threadless design has made the assembly of the device simpler and less traumatic. The assembled donor and KPro unit is sutured into a trephined host as in a traditional PK.19 Although a few case series of Boston type I KPro have been reported,56 the first multicenter study was published in 2006 by Zerbe et al.20 Zerbe et al.20 evaluated the indications, practices, complications, and outcomes of type I Boston KPro in 141 surgical procedures performed at 17 centers worldwide. They showed that KPro is a viable option for patients with multiple failed corneal grafts or in situations of poor prognosis for primary PK.

The purpose of our study is to report the indications, outcomes, and complications of the Boston type I KPro in Jordan and to compare our findings with the initial multicenter reports. To the best of our knowledge, this is the first study to of this kind from this region.

MATERIALS AND METHODS

Surgical procedure

The Boston type I KPro was obtained from the Massachusetts Eye and Ear Infirmary (Boston, USA). Details of the device and the surgical technique for implantation have been described in detail by Zerbe et al.20 Briefly, a donor button (8.5 mm) is prepared and a central 3-mm hole is trephined. The donor button is then placed over the stem of the front plate, and the back plate is then pressed into place on top. A titanium locking ring is then snapped into place to prevent loosening of the back plate. The recipient cornea is prepared as for a traditional PK (the usual host trephine is 0.25–0.50 mm less than the donor). If the patient is pseudophakic, the intraocular lens can be left in place; in phakic patients, a lensectomy and sometimes a core vitrectomy is performed. The donor graft with KPro is then sutured in place with multiple interrupted 10-0 nylon as with the standard PK. At the completion of the procedure, 400 μg of intracameral dexamethasone is often administered and a soft Kontour™ contact lens (Kontour Contact Lens, Richmond, CA, USA) is placed. All our patients had the adult type I Boston KPro except for one 10-year-old male with a chemical burn who underwent a pediatric Boston KPro procedure.

Data collection and analysis

A retrospective chart review was conducted to identify all patients who had undergone type I Boston KPro implantation from November 2007 to March 2010 at King Abdullah University Hospital, the only referral hospital in Jordan for KPro procedures. All surgeries were conducted by the same surgeon (WS). The study was approved by the Institutional Review Board (IRB) of King Abdullah University Hospital and Jordan University of Science and technology. All patients signed surgical consent forms preoperatively. Data gathered included demographics, diagnosis, prior surgeries, preoperative comorbidities, preoperative and postoperative visual acuities, and complications.

RESULTS

Twenty eyes of 19 consecutive patients (14 males, 5 females) between 10 years and 80 years of age (mean age: 51.7 ± 19.9 years; median age: 57 years) were included in this study. Mean postoperative follow-up was 18.1 ± 9.5 months (range: 3–36 months; median: 17.5 months). The patient who presented for the 3 months’ follow-up visit, died 1 month after this visit. The median number of prior corneal transplants was 2.0 (range: 0–3; mode: 2.0)

The primary corneal pathologies are presented in Table 1. Vascularized corneal opacity secondary to herpetic keratitis was the most common (eight eyes, 40%), followed by keratoconus (four eyes, 20%) [Table 1]. Preoperative comorbidities included glaucoma in five eyes (25%), limbal stem cell deficiency in four eyes (20%), and optic atrophy (that was diagnosed postoperatively) in three eyes (15%).

Table 1

Primary corneal pathology

Preoperative visual acuity was light perception in two eyes, hand motion in eleven eyes and counting fingers in -seven eyes. Figure 1 shows the best corrected visual acuity (BCVA) in patients with KPro. Postoperatively, BCVA improved significantly in 85% of cases (17 eyes), and this was maintained in 70% of cases (14 eyes) throughout the follow-up period. BCVA reached 20/200 or better in 13 eyes (65%). One quarter of eyes (five eyes) had postoperative BCVA of 20/50 or better. Vision showed no improvement in three eyes with optic atrophy. Table 2 presents the vision, classified according to age and preoperative diagnosis. BCVA ≥20/50 was achieved in 55.6% of patients aged ≤55 year but in none of the patients >55 years (P=.008). The percentage of eyes with improved postoperative vision and the percentage of eyes achieving BCVA ≥20/200 did not differ significantly according to age-group [Table 2]. In the subgroup of 15 eyes followed for at least 1 year (median follow-up: 20 months; range: 12–36 months) after KPro implantation, vision improved in 86.7% of eyes; it was 20/200 in 66.7% of eyes and 20/50 in 26.7% of eyes.

Figure 1

Postoperative best corrected visual acuity in eyes with the Boston type I keratoprosthesis

Table 2

The percentage of eyes with visual improvement after Boston type I keratoprosthesis implantation, according to age and preoperative diagnosis

The most common complication was retroprosthetic membrane (RPM) formation which occurred in nine eyes (45%). Other complications included extrusion of the implant in two eyes (10%), glaucoma and progression of a preexisting glaucoma in four eyes (20%), keratitis in two eyes (10%), endophthalmitis in one eye (5%) and sterile vitritis in one eye (5%).

DISCUSSION

The Boston KPro was developed for patients in whom a traditional full-thickness corneal transplant would likely fail.19 All the patients in our study had multiple prior failed grafts except for one patient with OCP who had a primary KPro. A previous study of Boston KPro patients demonstrated that eyes with prior transplant failure due to noncicatricial causes had the best prognosis (83% of those achieving vision of at least 20/200, which was maintained at 2 years), followed by OCP (72%), chemical burns (64%), and SJS (33%).15

Zerbe et al.20 also reported good outcomes for patients with chemical burns and noncicatrizing graft failure [94% and 90%, respectively, of eyes achieving at least 20/200 vision maintained at the last follow-up (average: 8.5 months)]. These results correspond well to the findings in our study. We found that the best maintained outcome was in patients with noncicatrizing graft failure [Table 2].

With refinements in the manufacturing technique and improvements in surgical and postoperative management, patient outcomes have improved.2122 Our results are consistent with previous reports. For example, most patients had significant improvement in vision after the KPro (85%); BCVA reached 20/200 or better in 13 eyes (65%), and 5 eyes (25%) had postoperative BCVA of 20/50 or better. Those without significant improvement or worsening of vision generally had underlying advanced glaucoma or retinal pathology. In our series, the three eyes that showed no significant improvement in vision were found to have optic atrophy.

The rate of device retention was more than acceptable in our series. All eyes retained their prostheses during the follow-up period except for two (10%): one with OCP and another eye that developed melting. In both cases, there was extrusion of the KPro (at 12 and 15 months after the implantation, respectively) and further surgery was required to restore the integrity of the globe.

RPM formation was the most frequent postoperative complication in our study (45%). This outcome was more frequent than in the Boston KPro multicenter study (25%),20 in prior published data (27%–35%),23 and with AlphaCor keratoprosthesis (9.3%).24 All cases of RPM in our study were successfully treated with YAG laser only. The etiology of RPM has yet to be determined. One hypothesis is that RPM is caused by inflammatory cells reacting to the polymethyl methacrylate material of the KPro.18 However, no studies to date have proved this hypothesis.

Glaucoma is a common complication after keratoprosthetic procedures.20232526 Glaucoma constitutes a challenging problem that significantly affects the outcome of KPro. Some patients may have preexisting glaucoma that may progress postoperatively and others may develop glaucoma after the KPro procedure. Another challenge comes from the difficulty in assessing the intraocular pressure postoperatively as this is dependent on digital palpation. Modalities for imaging of the optic nerve head and retinal nerve fiber layer may allow reproducible surveillance of optic nerve head changes in the future.18 In our series, five eyes had prior glaucoma that was controlled with antiglaucoma medications. However, the condition in two of these eyes continued to progress and required cyclodestruction (cyclodiode). Another two eyes (10%) developed high intraocular pressure, which was controlled medically. Endophthalmitis occurred in one eye in our series (5%). This patient had stopped the fortified topical vancomycin on his own initiative. The vitreous tap showed gram-positive organisms and the patient responded to intravitreal antibiotics. The rate of endophthalmitis has been higher in prior series (10.8% in the series by Chew et al.18 and 12% in that by Nouri et al.22). We routinely prescribe 14 mg/ml topical vancomycin to all patients undergoing KPro as previous studies have reported that this can reduce the incidence of endophthalmitis.2027–29 Two eyes (10%) developed keratitis that was treated successfully with fortified antibiotics. One patient developed sterile vitritis (5%) that was treated initially as endophthalmitis; this patient was later found to have a negative vitreous tap and responded well to periocular steroids

To the best of our knowledge, this is the first study from the Middle East that reports the outcomes of Boston KPro implantation over this range of follow-up. One of the limitations of this study is the small sample size and the short follow-up of some of the cases. This number should increase in the near future since our center is now established as a referral center for KPro procedures in the region.

CONCLUSION

Boston KPro appears to be a reasonably safe and effective solution for patients with corneal blindness in whom the prognosis for natural corneal grafting is poor. Retention rates are acceptable and there is valuable vision improvement. Complications are not uncommon and require frequent follow-up and timely intervention. Patient selection is a key factor in the successful outcome of this procedure.