Menoufia Medical Journal

: 2019  |  Volume : 32  |  Issue : 4  |  Page : 1441--1446

Outcome of keratoprosthesis implantation in end-stage corneal diseases

Ehab S Othman1, Hany A Khairy1, Sameh S Mandour1, Mahmoud Y Mahmoud2,  
1 Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Ophthalmology, Eye and Laser World, Giza, Egypt

Correspondence Address:
Mahmoud Y Mahmoud


Objective The objective of this study was to evaluate the indications, outcomes, and complications of keratoprosthesis (type I Boston keratoprosthesis) in end-stage corneal disease. Background Corneal diseases are the leading cause of blindness worldwide, second after cataract. Eyes with deep corneal vascularization, limbal stem cell deficiency, autoimmune diseases, and chemical injury are prone to graft rejection. Keratoprosthesis offers visual rehabilitation in such situations. Patients and methods In this prospective clinical study, 10 eyes of 10 patients with an end-stage corneal disease underwent implantation of type I Boston keratoprosthesis, with a mean follow-up of 6.9 ± 1.4 months. The indications included multiple failed grafts (n = 6), ocular cicatricial pemphigoid (n = 3), and vascularized corneal opacity (n = 1). Antibiotic prophylaxis was administered postoperatively, and patients were followed up at 1 week, 1, 3, and 6 months. The main outcome measures were best-corrected visual acuity, retention of prosthesis, and complications. Results The most common indication for keratoprosthesis implantation was graft failure (6/10, 60%). Mean best-corrected visual acuity improved significantly after the surgery (P = 0.018). Nine (90%) patients had final visual acuity of 20/200 or better. Ten (100%) of 10 patients had retained keratoprosthesis. Complications occurred in only two (20%) patients, where one (10%) patient had keratitis and one (10%) patient had peripheral corneal melting. Conclusion Boston keratoprosthesis provides improved vision for patients having corneal blindness owing to end-stage corneal diseases; however, long-term studies are needed to monitor the late-onset complications in the postoperative period.

How to cite this article:
Othman ES, Khairy HA, Mandour SS, Mahmoud MY. Outcome of keratoprosthesis implantation in end-stage corneal diseases.Menoufia Med J 2019;32:1441-1446

How to cite this URL:
Othman ES, Khairy HA, Mandour SS, Mahmoud MY. Outcome of keratoprosthesis implantation in end-stage corneal diseases. Menoufia Med J [serial online] 2019 [cited 2020 May 31 ];32:1441-1446
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Corneal diseases are the leading cause of blindness worldwide, second only to cataract. Severely diseased corneas with deep vascularization, limbal stem cell deficiency, autoimmune diseases, chemical injury, etc., are prone to graft rejection after penetrating keratoplasty. Despite the improvements in corneal lamellar surgical techniques and limbal stem cell transplantation, and a widespread usage of immunosuppression, graft survival has not improved in autoimmune diseases, chemical injuries, and dry eyes [1]. Thus, keratoprosthesis (KPro) seems to offer visual rehabilitation in such situations where corneal transplantation has an extremely poor prognosis [2],[3].

KPro, an artificial cornea, was developed to treat patients whose corneas are at high risk of immunological rejection after penetrating keratoplasty, or corneas with factors that might predispose them to graft failure after a failed penetrating keratoplasty [4].

KPro surgery often is considered a procedure of last resort for patients with bilateral severe corneal opacification after multiple unsuccessful cadaveric corneal transplants. However, indications have broadened to unilateral or bilateral corneal opacification after repeated graft failure, ocular trauma, herpetic keratitis, limbal stem cell deficiency, aniridia, Stevens–Johnson syndrome, silicone oil keratopathy, and congenital corneal opacification [5].

Boston KPro, a new design of artificial cornea available in type 1 and type 2 configurations (with type 1 being the most common, and type 2 reserved for end-stage ocular surface disease desiccation), has resulted in positive clinical outcomes in the treatment of corneal blindness. It is also subject to complications, such as the development of retroprosthetic membrane, glaucoma, and infectious endophthalmitis [6],[7].

In this study, we aimed to evaluate the indications, visual outcome, and complications of KPro implantation in patients with end-stage corneal diseases.

 Patients and Methods

This was a prospective observational study, which was carried out on 10 eyes in patients who underwent type I Boston KPro implantation owing to end-stage corneal disease. Patients were selected from 'Ophthalmology Department of Menoufia University Hospitals' and Eye and Laser World Hospital in Giza, from June 2016 to June 2017. After receiving the approval of the Institute Ethical Committee, all patients received a thorough explanation of the study design and aims. The study was conducted in compliance with informed consent regulations.

Inclusion criteria were visual acuity (VA) less than 20/400 up to perception of light with intact nasal light projection owing to bilateral corneal opacification with repeated transplantation failure or high risk of graft rejection owing to autoimmune disease, highly vascularized cornea, and cicatrizing condition, for example, Stevens–Johnson syndrome, ocular cicatricial pemphigoid, and ocular burn. Exclusion criteria included VA more than 20/400, poor blinking and tear mechanism, retinal detachment, extreme optic nerve cupping, and patient with advanced glaucoma (shunt should be considered).

The preoperative evaluation included history taking and ocular examination. This included slit lamp evaluation to see the status of the conjunctiva, ocular surface, cornea, and lens. The parameters evaluated were the best-corrected visual acuity (BCVA), intraocular pressure (IOP), and tear film status (Schirmer's test and break-up time). An ultrasonography was done for posterior segment evaluation and lens status. Biometry was done with confirmation of phakic, pseudophakic, aphakic presence to determine adequate KPro type and focal length. Electrophysiological studies included electroretinogram and visual evoked potential.

KPro surgery was performed under local or general anesthesia. All the surgeries were performed by a single experienced surgeon. A corneal graft (8.5 mm in diameter) was prepared using a hand-held circular trephine, and a central 3.0 mm hole was trephined with a dermatological punch that was provided with the KPro assembly [Figure 1]. The graft with the central hole was slid over the KPro stem using the provided pin. Methylcellulose 2% was applied to the posterior surface of the graft. The locking ring was pressed on to the lead stem with a finger. The hollowed pin was used to press the ring firmly down into the groove, usually with an audible snap. The assembly was inspected for the correct position of ring [Figure 2]. The graft–prosthesis combination was removed from the adhesive and stored in McCarey–Kaufman media while the recipient bed was prepared. The patient's cornea was trephined 0.5 mm smaller than the prepared graft [Figure 3]. In phakic eyes, the natural crystalline lens was removed by open-sky extracapsular extraction. In aphakic eyes, a Flieringa ring was used, and core vitrectomy was performed. The graft–KPro assembly was then placed over the recipient bed and secured with 16 10-0 monofilament nylon interrupted sutures [Figure 4]. At the end of the surgery, 400 mg of intracameral dexamethasone sulfate was given, and a semipermeable soft contact lens (Kontur, 16.0 mm diameter, 9.8 mm base curve) was placed.{Figure 1}{Figure 2}{Figure 3}{Figure 4}

Immediately postoperatively, all patients were treated with antibiotic drug (gatifloxacin or moxifloxacin administered four times per day) at least four times daily. In addition, a topical steroid (prednisolone acetate 1% or available drug) was required. A tapered regimen was initiated at eight times per day for 1 week, four times per day for the next 3 weeks, and reduced over a 1–3 months postoperative period. At 6 months, all patients were on chronic steroid drops four times per day thereafter. Moreover, 5% povidone iodine drops were administered once per month at follow-up visits.

After the surgery, the patients were followed up daily during their stay in the hospital. Thereafter, they were examined at 1 week, 1, 3, and 6 months. BCVA, air puff tonometry, and bandage contact lens (BCL) position were checked at each visit. Furthermore, the apposition of graft–host junction, presence of epithelial defect, stromal necrosis, or suture-related complications, if any, were noted. At each visit, cleaning with povidone iodine was performed, and the BCL was changed at 3 months.

Statistical analysis

Statistical analysis was done by IBM SPSS, v21.0 statistical software (IBM Corp., Armonk, New York, USA). Descriptive statistics was calculated, and the data were summarized as mean ± SD, or frequencies (number of cases) and percentages when appropriate. Comparisons between preoperative and postoperative VA at different visits were done using repeated measures analysis of variance with Bonferroni's correction. Subgroup comparisons in individual visits were done using Mann–Whitney U-test or Kruskal–Wallis test as appropriate. Pie charts were used for categorical data representation, whereas line graphs were used to represent means of numerical data across visits. The results were considered statistically significant at P value less than 0.05.


The mean age of the patients was 51.50 ± 18.12 years (range: 15–68 years) with five females and five males. The most common indication for which KPro was implanted was failed graft (6/10), followed by ocular cicatricial pemphigoid in three eyes, and vascularized corneal opacity and descemetocele in one eye [Table 1]. In patients with failed graft, the average number of keratoplasties performed previously was 2.14 ± 0.37.{Table 1}

The preoperative BCVA was hand movements close to face in six eyes, counting fingers in three eyes, and perception of light with poor project in one eye. Among the 10 patients implanted with KPro, three had preoperative glaucoma. Of these three patients, one need simultaneous implantation of Ahmed glaucoma valve. The other two patients had controlled IOP, that is, less than 25 mmHg with single topical antiglaucoma medication [Table 2].{Table 2}

Mean BCVA improved significantly after the surgery (P = 0.018) [Table 3].{Table 3}

Nine patients (90%) had final VA of 20/200 or better at mean follow-up of 6.9 ± 1.4 months. At the last follow-up visit, one eye had a vision of 20/25, whereas two eyes had a vision of 20/40, two eyes had a vision of 20/100 and one eye had a vision of 20/50. Among the 10 patients followed up for a mean period of 6.9 ± 1.4 months, six patients achieved BCVA better than 20/40 at some point in the postoperative period. [Figure 5] illustrates the variation of mean VA in the postoperative period.{Figure 5}

Complications occurred in only two (20%) patients, including one (10%) patient who had keratitis (stromal infiltration) treated with fortified ED eye drop (fortum vancomycin diflucan), and one (10%) patient who had peripheral corneal melting TTT with patch graft [Figure 6]. The remaining eight (80%) patients had no complication during the follow-up period.{Figure 6}

At the final follow-up, the prosthesis was retained in 100% of the patients.

No case of endophthalmitis was noted.


The high-risk, end-stage corneal blindness conditions present a treatment challenge because of high rejection and failure rates. The different treatment options for such cases are traditional keratoplasty with systemic immunosuppression, KPro, and bioengineered, collagen-based corneal scaffolds [8].

The long-term immunosuppression carries a high risk of systemic adverse effects, whereas bioengineered scaffolds are still in the experimental stage. Hence, KPro remains the only practical option for these patients. Boston KPro was approved by the US Food and Drug Administration in 1992 and is currently the most commonly used KPro in the world.

Similar to most of the previously published studies [9],[10],[11], the commonest indication for surgery in our patients was failed graft.

Mean BCVA improved significantly after the surgery (P = 0.018). Nine (90%) patients had final VA of 20/200 or better at mean follow-up of 6.9 months. These results are comparable with the previous studies of Boston KPro by Zerbe et al. [12], where 57% eyes achieved BCVA of at least 20/200 at an average follow-up of 8.5 months; Aldave et al. [9], where 75% eyes achieved BCVA of at least 20/100 after 1 year; Chew et al. [13], where 89% eyes achieved BCVA of at least 20/200 after 14 months; and Bradley et al. [14], with 75% eyes achieving BCVA of at least 20/200 at an average of 28 months.

Although the final VA was better when compared with the preoperative level, the final BCVA was less than the maximum VA attained over a period of time. This can be attributed to events like inflammatory debris, sterile vitritis, and progressive glaucoma. This was in contrast to the results by Aldave et al. [9], where the BCVA remained unaffected over 2 years after the initial exponential gain in the postoperative BCVA. Chew et al. [13] also noted a similar decrease in the mean visual acuities during the follow-up period. It is important to warn the patients about the decrease in the BCVA, which may occur after KPro implantation owing to long-term complications.

All of the 10 KPro were retained at the last follow-up (mean follow-up: 6.5 ± 2.1 months). The Boston KPro type I study group reported retention rate of 95% in 141 eyes, with an average follow-up time of 8.5 ± 6.1 months. Zerbe et al. [12] reported a retention rate of 95% over 8.5 months. Chew et al. [13] reported a retention rate of 100% over 16 months. Ciolino et al. [15] reported a retention rate of 93% over 17.1 months. The overall retention rate in our study is comparable with the previously published results.

Complication occurred in two (20%) patients in our study. Infective keratitis was noted in one (10%) case, which was treated with fortified E.D (fortum vancomycin diflucan). These results are comparable with the previous studies of Boston KPro by Zerbe et al. [12] (not reported), Aldave et al. [9] (11.9%), Greiner et al. [16] (0%), Chew et al. (0%) [13], Ciolino et al. [15] (not reported); and Srikumaran et al. [11] (3.4%).

There was no case of infectious endophthalmitis in our study. However, there is a need for continued follow-up in any patient receiving KPro, especially in settings where patients may be coming from long distances for care and from areas of economic disadvantage.

Endophthalmitis occurs in previous studies of Boston KPro by Zerbe et al. [12] (0%), Greiner et al. [16] (12.5%), Chew et al. [13] (11%), Ciolino et al. (3%) [15] (3%), and Srikumaran et al. [11] (15.5%).

In our study, one (10%) patient had peripheral corneal melting, which was treated with patch graft. The incidence of corneal melt in Boston KPro is reported to be anywhere between 1.5 and 17% [9], although not all cases reported a drop in vision. The patient in our study reported a drop in vision few months after the additional surgery. It can be because of the fact that the melts in their study were small (2 mm) and were managed with the application of cyanoacrylate glue and BCL, whereas our patient required scleral patch graft because of larger melts.

Incidence of corneal melting in previous studies of Boston KPro by Zerbe et al. [12] was 3.5%, Greiner et al. [16] was 15%, Chew et al. [13] was 8%, Ciolino et al. [15] was 3%, and Srikumaran et al. [11] was 19.5%. Although the modification of KPro design to include 16 backplate holes has lowered the incidence of corneal melt, the risk can be further minimized by using a bandage soft contact lens [13]. The exact pathogenesis of corneal melt after KPro surgery is poorly understood. The various factors implicated are the formation of retroprosthetic membrane (RPM), which blocks the holes on the backplate, thereby decreasing the nutrient supply to the tissue; increased collagenase activity; exposure keratitis; and dry eyes [15].

Sterile melts can be managed conservatively by improving the tear film using topical lubricating drops. Anticollagenolytic agents, such as topical medroxyprogesterone and oral tetracyclines, can also be used to prevent further melting. Surgery is imperative in unresponsive cases. The different surgical options include amniotic membrane grafting, buccal mucous membrane grafting (BMMG), donor corneal lamellar graft, or a repeat Keratoprosthesis (KPro) surgery if everything fails [17]. The percentage of patients with pre-existing glaucoma was 30% compared with 52% in a multicenter Boston type I KPro study done by Aldave et al. [9], 76% in study done by Patel et al. [18], 66% in a study done by Bradley et al. [14], and 73% in a study done by Chew et al. [13]. The same number of patients continued to have glaucoma in the postoperative period. Concomitant AGV was implanted in one patient during the KPro surgery. In the international series by Aldave et al. [9], 13.9% of patients continued to have raised IOPs, and 8.9% required surgical intervention. Multiple previous surgeries, anatomic changes in the anterior segment and long periods of steroid treatment contribute to the glaucoma in these patients. Continued monitoring of IOP is recommended in all the patients undergoing KPro surgery [19],[20].

The overall results of our study is comparable with the previous studies of Boston Kpro regarding visual outcome, retention of the device, and incidence of complication, although studies with larger sample size and longer follow-up are need to be done before conclusively establishing the efficacy of this device.


Boston KPro provides improved vision and improved quality of life for patients having corneal blindness owing to end-stage corneal diseases. However, the trend of decrease in the BCVA over a period of time warrants long-term studies to monitor the late-onset complications in the postoperative period.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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