Outcomes of Repeat Boston Type 1 Keratoprosthesis Implantation


To describe the outcomes and prognostic characteristics of patients who had a repeat Boston type 1 keratoprosthesis (KPro) implantation.


Retrospective case series.


setting : Data regarding preoperative clinical and demographic characteristics and postoperative course during initial and repeat KPro placement were collected at multiple centers across the country. patients : Forty-eight eyes underwent explantation of KPro owing to complications between September 2003 and August 2014 at 5 participating tertiary eye care centers in the United States. Of those, 36 eyes that received a subsequent replacement device were included. main outcome measures : Visual acuity (VA) outcomes and postoperative complications.


Ocular surface disease was significantly more common in eyes that required a device explantation, compared to those that retained the device ( P < .001). Sixty-seven percent of eyes (24/36) achieved VA ≥20/200 vision after the repeat KPro. The probability of these 24 eyes maintaining VA ≥20/200 after the repeat KPro was 87% at 1 year and 75% at 2 years. Predictors of the ability to maintain vision ≥20/200 following surgery were a better last-recorded vision before explantation ( P = .0002) and better vision immediately after repeat KPro ( P < .001).


Ocular surface disease and its complications were associated with more frequent device removal. In these patients, repeat KPro resulted in restoration of vision. A reasonable visual acuity prior to device removal was associated with favorable long-term postoperative visual acuity and retention.

The Boston type 1 keratoprosthesis (KPro) has become an increasingly frequent corneal procedure over the past decade, owing to its favorable anatomic and visual outcomes. Hence there is a growing body of literature supporting the use of this device in many clinical situations where donor corneal transplantation would be deemed not feasible.

Retention has been a frequently reported outcome. The most recent large retrospective multicenter cohort demonstrated an overall rate of 67% at 7 years. Considering the recently renewed popularity of the KPro and its increasingly frequent use worldwide, surprisingly few reports have specifically examined the outcomes of those patients who required device removal owing to complications. While some patients require a tectonic penetrating keratoplasty when there is no salvageable vision, a considerable number of patients undergo an exchange of KPro device following explantation. Currently, there are no guidelines as to who might benefit from a repeat KPro and who should not receive another device owing to predicted poor outcomes. As such, the ideal candidates for repeat KPro implantation remain ambiguous. In this study, we examine outcomes of the largest multicenter cohort of patients who underwent repeat KPro implantation, and attempt to describe those patients who may benefit most from device reimplantation.


This is a retrospective multicenter review of patients who underwent repeat Boston type 1 KPro implantation by 5 high-volume KPro surgeons at 5 tertiary care referral centers in the United States (Albany Medical Center Department of Ophthalmology, Albany, New York; Flaum Eye Institute, Rochester, New York; Stein Eye Institute, Los Angeles, California; Wills Eye Institute, Philadelphia, Pennsylvania; Wilmer Eye Institute, Baltimore, Maryland). All adult patients that underwent initial KPro surgery between September 30, 2003 and December 18, 2006 were considered. September 2003 was used as a cutoff in order to include only the eyes that received the fenestrated back plate device with lower complication rates (than the outdated solid back plate). A detailed description of the participants, surgical technique, and follow-up care can be found elsewhere. Additional consecutive patients who met the study criteria and had their surgeries after December 2006 at 2 centers (Wilmer Eye Institute; Stein Eye Institute) from January 2007 to August 2014 were also included. The study was reviewed and approved by the Institutional Review Board at each site in accordance with the Declaration of Helsinki and was Health Insurance Portability and Accountability Act compliant.

Data Collection and Analysis

Information from each patient’s medical record was collected retrospectively between May 2011 and April 2015 and entered in a uniform Microsoft Excel spreadsheet (Microsoft Corp, Redmond, Washington, USA) at each site. De-identified data were then reviewed by 2 of the authors (S.A. and P.M.) for completeness and consistency. Patients under the age of 18 years at the time of surgery or without at least 1 postoperative follow-up visit were excluded from the analyses. All eyes with at least 1 postoperative visit and at least 6 months of follow-up were considered. Clinical data on patient demographics, ocular history, the indication for initial KPro surgery, reason for KPro removal, preoperative visual acuity (VA), surgical details, postoperative vision at 6 months and recorded yearly thereafter, and best-ever visual acuity after initial KPro and after repeat KPro, as well as postoperative complications, were collected from the patients’ medical records. Ocular surface disease (OSD) was defined as severe keratoconjunctivitis sicca, cicatrizing conjunctivitis from chemical or thermal trauma, or autoimmune or inflammatory conditions such as mucous membrane pemphigoid, Stevens-Johnsons syndrome (SJS), or atopic disease. The decision to perform a repeat KPro vs a tectonic graft was made by the operating surgeon and largely based on the visual potential of the patient as well as the type of complication necessitating the removal of the device.

Best-corrected Snellen acuity was recorded as a primary outcome and was converted to logMAR VA for the purposes of the analysis. Counting fingers (CF), hand motion (HM)/light perception (LP), and no light perception (NLP) visual acuity were converted to logMAR 1.8, 2.3, and 2.6, respectively.

Statistical Analysis

The data were entered in Microsoft Excel spreadsheets and further statistical analysis was performed using Stata software version 13.1 (Stata Corp, College Station, Texas, USA). Patient outcomes were estimated using Kaplan-Meier survival curves for all patients with an initial KPro and separately for all patients with a repeat KPro. Success was defined in 2 ways: (1) maintenance of ≥20/200 vision following initial or repeat KPro implantation; and (2) maintenance of vision better than preoperative (before the initial KPro) vision. Eyes were censored if they were lost to follow-up within 6 months after surgery or underwent removal of the repeat device. Further analysis was then performed on eyes in which repeat KPro implantation was performed to assess differences in outcomes and characteristics predictive of success. The χ 2 test was used for categorical variables and Student t test for continuous variables. Fisher exact test was substituted for comparisons with inadequate sample size (n < 5). A value of P < .05 was considered significant.


Baseline Characteristics and Rates of Retention

A total of 174 eyes of 165 patients underwent KPro implantation surgery for the first time between September 2003 and June 2013 at the above-mentioned sites. Of these, 13 patients (15 eyes) were under the age of 18 at the time of surgery, 4 patients (6 eyes) had no postoperative follow-up data, and 5 patients (5 eyes) had less than 6 months of follow-up and thus were excluded from the analysis. The remaining 148 eyes of 143 patients were included. The mean follow-up for the initial KPro implantation was 48.9 ± 23.9 months (range, 7 months – 8.7 years) with roughly half of the eyes (47%) having greater than 4 years of follow-up. The overall retention rate was 67% (99/148) over 48.9 months. Thirty-six eyes of 35 patients underwent a repeat KPro implantation.

Ocular surface disease was more common in eyes that required explantation of the device (22/49, 50%) (SJS [n = 4], mucous membrane pemphigoid [MMP] [n = 5], cicatrizing keratoconjunctivitis [n = 5], graft-vs-host disease [n = 1], prior chemical injury [n = 3]) than in the eyes in which the initial KPro was retained (14/99, 14%; P < .001).

The average time period between the initial and the repeat KPro in these 36 eyes was 25 months (range, 1.1–73 months). The average follow-up period following the repeat KPro was 22.7 months (median, 20.8 months; range, 1–62 months). The baseline clinical characteristics and reasons for removal of these patients are listed in Table 1 .

Table 1

Baseline Characteristics of Study Participants Who Received a Boston Type 1 Keratoprosthesis

Patients With Initial KPro (N = 120) Patients With Repeat KPro (N = 36)
Age (y) 64.8 57.7
Female sex (%) 66 (55.0%) 20 (55.6%)
Preoperative diagnoses
Ocular surface disease 21 (17.5%) 18 (50.0%)
Infectious etiology 14 (11.7%) 7 (19.4%)
Congenital corneal abnormalities 17 (14.2%) 4 (11.1%)
Fuchs dystrophy/bullous keratopathy/keratoconus 47 (39.2%) 5 (13.9%)
Unknown etiology 21 (17.5%) 2 (5.6%)
Glaucoma 66 (55%) 23 (63.9%)
Preoperative visual acuity
Visual acuity of surgical eye, mean logMAR/Snellen 1.86 / CF (0.52) 2.05 / CF (0.41)
Visual acuity of fellow eye, mean logMAR/Snellen 1.15 / 20/280 (0.96) 1.44 / 20/550 (0.97)
Visual acuity
Best-corrected visual acuity after first KPro surgery, logMAR/Snellen 0.83 / 20/135 (0.74) 0.65 / 20/93 (0.57)

CF = counting fingers; KPro = keratoprosthesis; logMAR = logarithm of the minimal angle of resolution.

Values represent mean (standard deviation) for continuous variables and frequency (percentage) for categorical variables.

Visual Acuity Outcomes

The visual acuities before initial KPro, after initial KPro, and after repeat KPro are demonstrated in Figure 1 and specified in Table 2 . Sixty-seven percent of patients who had a repeat KPro achieved visual acuity ≥20/200 and 75% were ≥20/400.

Figure 1

Best recorded vision of patients who received a repeat Boston type 1 keratoprosthesis (KPro): before initial KPro, after initial KPro, and after repeat KPro (n = 36). VA = visual acuity; CF = counting fingers; HM = hand motion; LP = light perception; NLP = no light perception.

Table 2

Visual Acuity Outcomes and Complications of Study Participants Who Received a Boston Type 1 Keratoprosthesis

Patients With Initial KPro (N = 112) Patients With Repeat KPro (N = 36) P Value
Visual acuity outcomes
Visual acuity, surgical eye, mean logMAR (range) 1.85 (0.39–2.3) 2.05 (1–2.3) .03*
Visual acuity of fellow eye, mean logMAR (range) 1.16 20/280 (0–2.6) 1.44 (0–2.6) .13
Best-ever vision, after initial KPro, mean logMAR (range) 0.80 (0–2.6) 0.65 (0–1.8) .25
Best-ever vision, after repeat KPro, mean logMAR (range) 0.97 (0–2.6)
Visual acuity at last follow-up, mean logMAR (range) 1.36 (0.09–2.6) 1.4 (0–2.6) .8
Complications after initial KPro
Retroprosthetic membrane 49 (43%) 20 (55.6%) .22
Persistent epithelial defects 4 (3.6%) 9 (25%) <.001*
Endophthalmitis 9 (8.2%) 6 (16.7%) .15
Sterile keratolysis 1 (0.9%) 9 (25%) <.001*
Corneal infiltrate 1 (0.9%) 9 (25%) <.001*
Glaucoma intervention 16 (14.5%) 6 (16.7%) .757
Complications after repeat KPro
Retroprosthetic membrane 1 (2.7%)
Endophthalmitis 6 (16.7%)
Sterile keratolysis 5 (13.9%)
Glaucoma intervention 4 (11%)

KPro = keratoprosthesis; logMAR = logarithm of the minimal angle of resolution.

Asterisk indicates statistical significance.

In survival analysis models, in the 23 eyes that achieved ≥20/200 vision after repeat KPro implantation, the probability of maintaining ≥20/200 was 92% at 6 months (95% CI: 71%–98%), 87% at 1 year (95% CI: 64%–95%), and 75% at 2 years (95% CI: 48%–89%). This is favorable in comparison to the initial KPro for all 148 eyes, in which the rate was 91% (95% CI: 83%–95%) at 1 year and 77% (95% CI: 67%–84%) at 2 years ( Figure 2 ).

Figure 2

Likelihood of maintaining ≥20/200 visual acuity at last follow-up visit among patients undergoing first-time Boston type 1 keratoprosthesis implantation (n = 156) vs those undergoing repeat Boston type 1 keratoprosthesis implantation (n = 36). VA = visual acuity.

The probability of maintaining vision better than the preoperative visual acuity (before initial KPro) after the repeat KPro was 93% at 6 months (95% CI: 77%–98%), 89% at 1 year (95% CI: 70%–96%), and 84% at 2 years (95% CI: 63%–94%). This is favorable in comparison to the initial KPro, in which the rate was 93% (95% CI: 87%–96%) at 1 year and 82% (95% CI: 74%–88%) at 2 years ( Figure 3 ).

Figure 3

Likelihood of maintaining >preoperative visual acuity at last follow-up visit among patients undergoing first-time Boston type 1 keratoprosthesis (KPro) implantation (n = 156) vs those undergoing repeat KPro implantation (n = 36). PreOp = Preoperative; VA = visual acuity.

Patients with OSD had a trend toward better visual outcomes. Of all patients who had underlying OSD, 46% (18/39) had no history of prior corneal transplantation. Interestingly, 61% (11/18) of patients who had a repeat KPro and OSD achieved ≥20/200 visual acuity after their repeat KPro with a mean visual acuity logMAR 1.31 (range, 0–2.6) at last follow-up, which is better than the overall repeat KPro group (logMAR 1.42; range, 0–2.6) ( P = .46).

Complications After Initial Keratoprosthesis

Complications after initial KPro are listed in Table 2 . There was a higher proportion of postoperative complications in patients that ultimately received a repeat KPro.

Many of the patients who developed complications such as corneal infiltrates, persistent epithelial defects, and endophthalmitis had OSD. Namely, 5 of the 9 patients who developed corneal infiltrates and 9 of 18 with sterile keratolysis had underlying OSD. These postoperative complications are consistent with the causes for removal, in which 75% had either corneal infiltrate or melt as the underlying etiology. Ocular surface disease was treated with bandage contact lenses to prevent persistent epithelial defects and dryness, tarsorrhaphy if there was corneal melt, and, in some scenarios, creation of a tarsal-conjunctival flap or buccal mucosal graft in patients with severe conjunctival pathology.

Complications After Repeat Keratoprosthesis

Complications after repeat KPro are listed in Table 2 . Six patients developed postoperative elevated intraocular pressure and 4 required glaucoma intervention. Of these, 1 required a pars plana vitrectomy for vitreous blockage of tube shunt, 1 had removal of intraocular lens implant, and 2 had a tube shunt placed. Of the 30 other patients that had well-controlled glaucoma during the course of their repeat KPro, 11 had prior glaucoma surgery.

Of the 6 patients that developed endophthalmitis after their repeat KPro, half had endophthalmitis during their initial KPro as well. Of those who developed sterile keratolysis after the second KPro, 3 of 5 had had sterile corneal melt during the initial KPro course as well. Seven out of 36 eyes (19.4%) underwent tarsorrhaphy during their repeat KPro course. There were no other associations found with postoperative complications, including retinal detachment, glaucoma surgery, retroprosthetic membrane, or melt. Of note, some cases designated as having endophthalmitis were the ones that underwent a tap and injection for intraocular inflammation but did not always have a positive vitreous culture for microbial growth. Therefore, some of these cases might have had sterile vitritis rather than endophthalmitis.

Of the patients who had a repeat KPro, 80% (29/36) retained the device throughout the duration of follow-up. Of the 7 eyes that required subsequent removal, sterile keratolysis was the primary cause (n = 5), followed by total funnel retinal detachment (n = 1) and extrusion (n = 1) in the setting of endophthalmitis. One eye had a history of SJS and underwent enucleation within 6 months of the repeat device implantation owing to having a blind, painful eye. Two eyes had removal greater than 6 months after the repeat KPro (mean 15.4 months; range, 7.4–20.8 months) and underwent penetrating keratoplasty for tectonic purposes following recurrent sterile keratolysis; the remainder had a third KPro placed. Of the 4 patients who had third KPros placed, 3 had an underlying diagnosis of OSD or infection, and 1 had a congenital corneal opacity.

Predictors of Successful Outcomes

In order to determine the clinical predictors of success after repeat KPro (defined as maintaining ≥20/200 or better than preoperative vision), we compared preoperative characteristics (before the initial KPro) and postoperative (after the initial KPro) complications between patients who received a repeat KPro and met success criteria and those who did not. Preoperative visual acuity (prior to initial KPro) had no significance for good visual acuity outcomes. A higher number of preoperative glaucoma medications was associated with inability to maintain ≥20/200 VA (0.23 vs 0.56; P = .23) ( Table 3 ).

Jan 6, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Outcomes of Repeat Boston Type 1 Keratoprosthesis Implantation
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