Purpose
To describe the characteristics of patients who had Boston keratoprosthesis (KPro) explantation and the outcomes of their subsequent management.
Design
Retrospective observational study.
Methods
Cases that underwent Boston type 1 KPro at University of Montreal Hospital Center between October 2008 and May 2012 were reviewed. Patients with KPro explantation were identified and compared to those with KPro retention. Visual acuity, expressed as logMAR, was followed as primary outcome.
Results
A total of 345.1 life-years of device implantation were included in the analysis. Among 110 operated eyes, 11 eyes had KPro explantation, corresponding to a failure rate of 0.03/life-year. KPro was explanted at 19.7 ± 10.5 (4–40) months post KPro. Indications included sterile keratolysis (n = 7), infection (n = 2), and hypotony and painful blind eye (1 each). Compared to patients with KPro retention, those requiring KPro explantation were associated with aniridia ( P = .0038), sterile keratolysis ( P < .001), retroprosthesis membrane ( P = .02), and intraocular inflammation ( P = .04). KPro exchange (n = 8), penetrating keratoplasty (n = 1), or evisceration (n = 2) were performed as a secondary intervention. Among patients with KPro explantation, 4 (36.4%) recovered better than baseline visual acuity at final visit. Posterior segment complications (n = 5, 62.5%) were the most common cause of permanent vision loss. Final visual prognosis correlates with pre-explantation visual function (r = 0.68, P = .02).
Conclusions
Boston KPro explantation is a serious complication. Aniridic eyes are at significant risk and have a shortened keratoprosthesis retention time. When managed appropriately, patients can recover significant vision.
Designed by Dr Dohlman’s group in the 1970s, the Boston keratoprosthesis (KPro) has become a promising therapeutic alternative for multiple ocular surface diseases, especially in those who have failed conventional penetrating keratoplasty or those who are expected to do poorly with penetrating keratoplasty.
A number of modifications have been applied in the past years to improve surgical techniques, prosthesis design, and postoperative care in order to decrease complication rates. However, despite these modifications, potentially vision-threatening complications remain a real concern. Common complications include sterile keratolysis, retroprosthesis membrane, glaucoma, infection, and posterior segment complications such as retinal detachment. In rare cases where complications persist or progress despite maximal medical therapy, an explantation of the KPro may become necessary.
With the expanding indications and growing use of Boston KPro worldwide, understanding and managing Boston KPro–related complications, including its explantation, is increasingly important. In this current paper, we aim to characterize patients who required KPro explantation at our institution and to describe their management and examine their clinical outcomes.
Methods
In this retrospective observational case series, we screened all patients who underwent Boston type 1 KPro implantation by a single surgeon (M.H.-D.) between October 20, 2008 and May 28, 2012 to identify those who required an explantation of their KPro. This study was approved by the Institutional Review Board at Centre Hospitalier de l’Université de Montréal (Montreal, Canada).
Preoperative Evaluation
Prior to the initial Boston KPro implantation, all patients received a complete ophthalmologic examination including A-scan and B-scan ultrasonography.
Boston Keratoprosthesis Surgical Technique and Postoperative Management
Initial surgical intervention consisted of implantation of the Boston type 1 KPro (Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA) with either a fresh or frozen corneal graft, performed according to the previously described technique. Additional extracapsular lens extraction was performed in phakic patients, and anterior vitrectomy was performed in aphakic patients. Sphincterotomy and iridectomy were done in nonaniridic patients. The postoperative regimen consisted of topical moxifloxacin (Alcon Canada Inc, Mississauga, Ontario, Canada) and prednisolone acetate 1% (Sandoz Canada Inc, Boucherville, Quebec, Canada) 4 times daily. Patients suffering from glaucoma were followed jointly with a glaucoma specialist. Herpes simplex virus (HSV) prophylaxis was used in all patients with this diagnosis. Patients were seen on post-KPro day 1, weekly for 4 weeks, then every 3 months thereafter.
Keratoprosthesis Explantation and Postexplantation Management
KPro explantation resulted from failure of anatomic retention, which included removal, extrusion, or loss of the eye. Prior to explantation, if the visual acuity was logMAR 2.8 or better (see Data collection) and the eye did not show signs of phthisis, either a penetrating keratoplasty or a KPro exchange was performed, depending on the availability of the KPro device. For eyes that are phthisical and those that had lost light perception (logMAR 2.9), evisceration was performed.
Following explantation, all patients were seen on postoperative day 1 and at 1 week and 1 month. Patients who received KPro exchange and penetrating keratoplasty were subsequently followed every 3 months, whereas those who underwent evisceration were followed on a yearly basis.
The postoperative drops regimen for penetrating keratoplasty and KPro exchange was the same as that of the initial KPro implantation (see Boston keratoprosthesis surgical technique and postoperative management). Eviscerated patients received topical combined tobramycin 0.3% and dexamethasone 0.1% ointment (Alcon Canada Inc, Mississauga, Ontario, Canada) 4 times daily for 1 week.
Data Collection
Operative reports and medical evolution notes were reviewed in detail for all patients. Distance best-corrected visual acuity (BCVA), expressed in logMAR system, was recorded as primary outcome. Of note, we used extrapolated values of 2.6, 2.7, 2.8, and 2.9 to represent visual acuity of counting fingers, hand motion, light perception, and no light perception, respectively. Other recorded parameters include baseline demographics and diagnosis, complications, and additional interventions.
Data Analysis
A Microsoft Excel spreadsheet (Microsoft Corp, Redmond, Washington, USA) was used to compile data and statistical analysis was performed with SAS 9.2 (SAS Institute Inc, Cary, North Carolina, USA). Continuous data were presented as mean ± standard deviation (minimum-maximum). For categorical data, percentage was provided. Patients with KPro explantation were compared to those with retained KPro. Fisher exact test was used for categorical variables and Student t test was used for continuous variables. Device retention (survival) was plotted using Kaplan-Meier curve; log-rank test was used for categorical variables when applicable. For the KPro explantation group, Pearson correlation was done on final BCVA and pre-KPro implantation BCVA, as well as on final BCVA and pre-explantation BCVA. A value of P < .05 was considered significant.
Results
Rate of Keratoprosthesis Explantation and Baseline Characteristics
A total of 110 eyes from 99 patients received type 1 Boston KPro implantation for the first time at our institution between October 2008 and May 2012. Average age of patients at the time of KPro implantation was 60.8 ± 16.4 (21–98) years and the average duration of follow-up was 40.0 ± 16.3 (1–68) months. Thirty-six patients (36.4%) were female. More than half of the eyes (53.6%) had a history of previous corneal graft failure(s); they had undergone an average of 1.90 ± 1.01 (1–5) penetrating keratoplasties prior to KPro implantation. There was no significant difference in sex ( P = .52), history of previous penetrating keratoplasty ( P = .11), or follow-up duration ( P = .78) in patients with retained vs explanted KPro ( Table 1 ). Patients with KPro explantation were significantly younger than those with retained KPro ( P = .008).
| Retained KPro | Explanted KPro | P Value | |
|---|---|---|---|
| Age (y) | 62.4 ± 16.0 | 47.4 ± 14.9 | .008 a |
| Female | 31 | 5 | .52 b |
| Previous PK | 56 | 3 | .11 b |
| Follow-up duration (mo) | 40.0 ± 16.8 | 41.1 ± 10.9 | .78 a |
At final follow-up, 90% of KPro were anatomically retained. Eleven devices were explanted over a cumulative 345.1 life-years of device implantation, corresponding to an explantation rate of 0.03/life-year. The average time to explantation was 19.7 ± 10.5 (4–40) months post-KPro. The overall device mean survival time was 37.7 ± 0.7 (standard error) months ( Figure 1 ).
Primary diagnoses consisted of a number of ocular surface diseases ( Table 2 ). In our series, aniridia was the only diagnosis strongly associated with KPro explantation ( P = .004). The mean device survival time in aniridic patients was 28.0 ± 1.4 (standard error) months, vs 38.9 ± 0.7 months in nonaniridic patients ( P = .0038, log-rank test) ( Figure 2 ). Many patients received additional interventions at the time of their KPro implantation ( Table 3 ). Combined extracapsular lens extraction showed significant association with KPro explantation ( P = .003), whereas combined intraocular lens removal was associated with KPro retention ( P = .03).
| Diagnoses | Retained KPro (n = 99), N | Explanted KPro (n = 11), N (Rate %) | P Value a |
|---|---|---|---|
| Autoimmune | 2 | 1 (33) | .27 |
| Chemical burn | 8 | 1 (11) | 1.00 |
| Aniridia | 20 | 7 (25.9) | .004 |
| Herpetic keratitis | 12 | 2 (14.3) | .63 |
| LSCD | 6 | 0 (0) | 1.00 |
| Trauma | 13 | 0 (0) | .36 |
| Fuchs dystrophy | 3 | 0 (0) | 1.00 |
| PBK | 19 | 0 (0) | .21 |
| Infectious ulcers | 3 | 0 (0) | 1.00 |
| Miscellaneous | 13 | 0 (0) | .60 |
| Intervention | Retained KPro (n = 99) | Explanted KPro (n = 11) | P Value a |
|---|---|---|---|
| Anterior vitrectomy | 71 | 6 | .30 |
| IOL removal | 44 | 1 | .03 |
| ECC removal | 26 | 8 | .003 |
| Pupilloplasty | 19 | 2 | 1.00 |
| Iridectomy | 24 | 2 | 1.00 |
| Goniosynechialysis | 61 | 4 | .12 |
| Tarsorrhaphy | 3 | 0 | 1.00 |
| Miscellaneous b | 3 | 0 | 1.00 |
b Miscellaneous: symblepharon repair (n = 2), air-fluid exchange/endolaser (n = 1).
Causes of Explantation
Among patients requiring KPro explantation, sterile keratolysis (7/11, 63.6%) is by far the most common indication. Of these 7 patients, 4 presented with acute spontaneous complete or partial extrusion, 2 presented with hypotony (<6 mm Hg) attributable to active leakage, and 1 presented with ectasia of the KPro complex.
Two patients underwent KPro explantation owing to infections. One developed Staphylococcus epidermidis endophthalmitis and subsequent KPro dehiscence. The other patient had corneal infiltrate that progressed to 360 degrees around the optical stem despite fortified antibiotic drops (vancomycin 50 mg/mL, tobramycin 14 mg/mL) and moxifloxacin (Alcon Canada Inc, Mississauga, Ontario, Canada) around the clock. The corneal culture was, unfortunately, inconclusive.
Finally, 1 patient had her KPro removed because of persistent hypotony without identifiable leakage. Another patient received explantation for a painful blind eye.
Management Following Explantation
Following explantation, the choice of secondary interventions was selected based on the patient’s remaining visual potential, as estimated by his or her visual acuity prior to explantation and by presence of phthisis (see Methods). Eight patients underwent KPro exchange, 1 had penetrating keratoplasty, and 2 had evisceration. These patients were subsequently followed for 20.4 ± 10.5 (3–35) months after explantation. Of note, 1 patient with Stevens-Johnson syndrome who received KPro exchange eventually went on to require a second explantation owing to wound dehiscence and KPro extrusion. A subsequent penetrating keratoplasty was performed, but the graft became opaque within 3 months. The details of clinical evolution of these patients are listed in Table 4 .
| Patientt No. | Dx | Explant. Indication | Secondary Intervention | Pre-KPro BCVA a | Pre-Explant. BCVA a | Final BCVA a | FU (mo) b | Postexplantation Evolution (Time With Reference to KPro Explantation, Tx) |
|---|---|---|---|---|---|---|---|---|
| 1 | Aniridia | Melt (ectasia) | KPro exchange | 1.2 | 1.3 | 0.9 | 28 | Early postoperative vitritis (2 wk, medical tx); IOP spike (1 mo, medical tx); RPM (starting at 2 wk, YAGM at 4 mo) |
| 2 | Aniridia | Melt (leakage) | KPro exchange | 2.8 | 2.6 | 1.3 | 35 | RRD (4 d, PPV/EL/AFE); dellen (2 mo, medical tx); panuveitis (7 mo, medical tx); RPM (8 mo, YAGM at 10 mo, regrowth at 14 mo); vitreous hemorrhage (13 mo, obs) |
| 3 | Aniridia | Infectious keratitis | KPro exchange | 2.6 | 2.7 | 2.9 | 29 | Small RPM (2 wk, obs); nonoperable tunnel RRD (1 mo, obs); phthisis with hypotony (3 mo, obs) |
| 4 | Aniridia | Melt (leakage) | KPro exchange | 2.7 | 2.6 | 1 | 12 | Preretinal hemorrhage (1 wk, obs); small RPM (2 wk, obs); IOP spike (2–4 wk, medical tx) |
| 5 | Aniridia | Melt (extrusion) | KPro exchange/RPM removal | 2.6 | 2.7 | 2.8 | 8 | RRD (4 dys, PPV/EL/AFE); inferior sterile melt with hypotony (1 mo, repair with suture/glue, persistence of leakage at 9 mo, evisceration proposed, declined by patient) |
| 6 | Aniridia | Melt (extrusion) | KPro exchange/RPM removal | 2.6 | – | 0.9 | 3 | VItreous hemorrhage (1 d, observation); RPM (2 mo, YAGM) |
| 7 | Aniridia | Hypotony | KPro exchange | 2.6 | 2.8 | 2.9 | 22 | Persistent hypotony with secondary RD (1 wk, obs); RPM (10 mo, obs) |
| 8 | Chemical burn | Melt (extrusion) | PK/Amb | 2.8 | 2.8 | 2.7 | 13 | PK failure with peripheral thinning (3 mo, medical tx) |
| 9 | HSV keratitis | Blind and painful eye | Evisceration/tarsorrhaphy | 2.7 | 2.9 | 2.9 | 22 | – |
| 10 | HSV keratitis | Melt (extrusion)/phthisis | Evisceration/implant | 2.7 | 2.7 | 2.9 | 19 | – |
| 11 | SJS | Endophthalmitis | KPro exchange/IV Abx/Amb | 2.8 | 2.8 | 2.9 | 33 | KPro extrusion (3 mo, PK/buccal mucosa graft); PK failure (3 mo post 2nd KPro explantation, obs) |
Visual Acuity Outcome
Pre-KPro BCVA was 2.6 ± 0.5 (1.2–2.8) logMAR in patients with KPro explantation and 2.5 ± 0.6 (0.4–2.8) in those with retained KPro. Following Boston KPro implantation, the best mean BCVA improved significantly in those groups, to 0.8 ± 0.6 (0.3–2.6) logMAR ( P < .001) and to 0.8 ± 0.7 (0–2.8) logMAR ( P < .001), respectively. In patients with retention failure, their BCVA deteriorated to 2.6 ± 1.1 (1.3–2.9) logMAR prior to explantation. Post explantation, BCVA showed smaller but still significant improvement (1.8 ± 0.9 [0.9–2.9] logMAR, P = .02) compared to the pre-KPro baseline. Final mean BCVA stabilized at 2.2 ± 0.9 (0.9–2.9) logMAR in the KPro explantation group and at 1.5 ± 1.1 (0–2.9) logMAR in the KPro retention group. No significant difference was found between the 2 groups for pre-KPro ( P = .38), best ( P = .75), and final ( P = .68) BCVA.
In the KPro explantation group (n = 11), at final visit, 5 patients (45.5%) lost light perception (2.9 logMAR) and 1 was at 2.8 logMAR. One patient’s final BCVA was at 2.7 logMAR owing to penetrating keratoplasty failure with no other known posterior segment or glaucomatous complications. We decided to delay her second KPro implantation because the patient was pregnant. Four patients (36.4%) had better-than-baseline visual acuity, with 3 (27.3%) seeing superior or equal to 1 logMAR.
In patients with KPro explantation, final BCVA showed positive correlation with pre-explantation BCVA (r = 0.68, P = .02) and did not seem to be influenced by pre-KPro baseline (r = 0.49, P = .13).
Complications and Additional Interventions
Complications after the initial KPro surgeries are listed in Table 5 . Retroprosthesis membrane, sterile keratolysis, posterior segment complications (eg, retinal detachment, vitreous hemorrhage), and progression of glaucoma were among the most common ones. Although keratolysis developed in 4 eyes post KPro explantation, only 1 was severe enough to require another KPro exchange. In the KPro explantation group, among the 8 patients with a final BCVA < 1 logMAR, visual loss was attributable to retinal detachment (n = 5), terminal glaucoma (n = 1), phthisis (n = 1), and penetrating keratoplasty failure (n = 1).
