This study was conducted in accordance with the tenets of the Declaration of Helsinki, Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines, and was registered on PROSPERO prospectively (ID: CRD420251036643).

A search strategy (Supplementary Material, Tables S1-S3), created in consultation with an academic librarian, was used to search MEDLINE (PubMed; 1946), Embase (Ovid; 1974), and Cochrane Central Register of Controlled Trials (CENTRAL) from inception to June 17, 2025. Studies were included if patients received a Boston type 1 KPro implant and glaucoma or ocular hypertension (OHT)-related outcomes were reported. Studies were excluded if (1) they reported outcomes for < 5 eyes, (2) KPro other than the Boston KPro Type 1 were exclusively reported, (3) patients were not explicitly monitored for the development or progression of glaucoma, and (4) study design was case series with less than 5 eyes, editorials, and reviews. Only reports in English were included. Studies with overlapping authorship, institutions, and/or study periods were evaluated for potential cohort overlap, and where overlap was suspected, only the study with the largest sample size and/or longest follow-up period was retained for quantitative analysis to reduce the risk of duplicate patient inclusion. Multiple studies from the same institution were included when study populations were determined to be distinct based on differences in study period, authorship, or reported cohorts.

Included studies were managed using Covidence (Melbourne, Australia). Two reviewers (A.A.O. and K.S.) independently completed title/abstract screening, full text review, and data collection in parallel. Discrepancies were resolved through discussion with a third review (A.A. and M.B.). The data extraction form was piloted on a sample of 5 studies to ensure clear and standardized data collection. The following data was collected for each included study:

• 1.

  Study characteristics: year, country, study design and duration;

• 2.

  Patient characteristics: number of patients, age, sex, number of eyes, duration of follow up, number of aphakic/pseudophakic devices, previous keratoprosthetics surgeries, and indication for surgery;

• 3.

  Pre-operative glaucoma-related characteristics: pre-operative glaucoma diagnosis, pre- or intra-operative glaucoma surgeries, average number of IOP lowering medications, pre-operative IOP, and pre-operative C/D ratio; and

• 4.

  Postoperative characteristics: number of eyes with glaucoma progression or de novo glaucoma, number of eyes requiring postoperative surgical glaucoma intervention, number of eyes with postoperative OHT, average number of glaucoma medications, IOP, and C/D ratio.

The primary outcome was incidence rate of new glaucoma or progression of existing glaucoma following Type 1 Boston Kpro implantation. Glaucoma incidence, progression, and elevated IOP were defined according to the criteria used by the individual study authors. Secondary outcomes included postoperative elevated intraocular pressure and glaucoma-related perioperative patient and surgical characteristics.

Two reviewers (A.A.O and K.S) utilized the Joanna Briggs Institute (JBI) risk of bias (RoB) tools to complete the RoB of included studies. The Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) framework was used to evaluate the certainty of evidence. Observational studies began at low certainty while RCTs began at high certainty. The 5 domains used for downgrading the evidence consisted of risk of bias, inconsistency, indirectness, imprecision, and publication bias. Discrepancies were resolved through discussion with a third reviewer (A.A and M.B).

Meta-analyses were performed using R (version 4.5.2; R Foundation for Statistical Computing, Vienna, Austria) for the following outcomes: any postoperative glaucoma event, incidence of new-onset glaucoma, progression of pre-existing glaucoma, and postoperative IOP elevation. Analyses of glaucoma incidence and progression were restricted to studies that explicitly reported the respective outcomes. Studies that reported the presence of preoperative glaucoma without specifying postoperative new-onset glaucoma or progression were not included in incidence- or progression-specific analyses to avoid outcome misclassification; however, these were included in the primary analysis assessing any postoperative glaucoma event. Incidence rates of postoperative events were pooled using random-effects meta-analysis to account for between-study heterogeneity. Pooled estimates were calculated using a random-effects model implemented as a random intercept logistic regression with proportions transformed using a logit transformation. A continuity correction of 0.5 was prespecified for studies with zero events. Both proportions and incidence rates were reported to capture complementary aspects of risk, with proportions reflecting cumulative postoperative glaucoma burden across studies and incidence rates (events per eye-year) accounting for differences in follow-up duration and enabling assessment of the temporal distribution of events. Between study heterogeneity was evaluated using Cochran’s Q and the I² statistic. Between-study variance (τ²) was estimated using a maximum-likelihood estimator. CIs (CI) for pooled estimates were calculated using a t-distribution while Clopper-Pearson CI were calculated for individual studies. Statistical significance was assessed using 2-sided tests, with p -values <.05 considered statistically significant where applicable. Prespecified subgroup analyses included (1) whether studies explicitly reported a definition of glaucoma vs studies that did not report how glaucoma was defined and (2) by study follow-up duration (<2 years, 2-4 years, and > 4 years). Sensitivity analyses were performed to assess the robustness of pooled estimates. These included leave-one-out analyses, exclusion of small studies (sample size < 30 eyes, and studies with a high risk of bias. For outcomes with a limited number of contributing studies, analyses were restricted to primary pooling and leave-one-out assessments. Descriptive statistics were used to summarize baseline demographic and clinical data.

The database search identified 2897 records, of which 1511 duplicates were removed, leaving 1372 records for title/abstract screening. Following initial screening, 166 articles underwent full-text review based on predefined eligibility criteria. Ultimately, 23 studies met inclusion criteria and were included in the systematic review, as summarized in the PRISMA flow diagram ( Figure 1 ). ^{,,,,,,,,,,,,,,,,,,,,,,} Of the included studies, 13 were case series, 9 cohort, and 1 case-control study. Twelve of these were primarily glaucoma related. There were no RCTs. RoB for observational studies was conducted using the JBI Critical Appraisal Checklist, and no studies were excluded on the basis of high risk of bias (Supplementary Material, Tables S4-S6). RoB assessments for each study design and key results are summarized in Figure 2 and Table 1 , respectively.

PRISMA flow diagram of all studies included in the systematic review and meta-analysis.

Distribution of risk of bias ratings by study design using Joanna Briggs Institute critical appraisal tools. 26 studies were case series, 18 cohort, and 1 case-control.

A total of 1482 eyes were included across all studies. Patient-level demographic data were available for 1402 patients consisting of 790 (60.8%) males, 460 (34.7%) females, and 152 (4.5%) of whom did not have sex reported. Age was reported in 12 studies, yielding an unweighted average of 54.5 years (SD = ±8.9) and study-level means ranging from 35.7 to 65.9 years. Across all studies that provided age distributions, reported individual patient ages ranged from 21 to 96 years old. Follow-up duration was reported in 14 studies and was similarly heterogeneous, with a mean of 39.4 months (±14.4) and reported ranges extending from 12 to 115 months. Reporting of lens status and procedural characteristics was incomplete, with data unavailable for a substantial proportion of eyes. Lens status was available in 946 eyes (63.8%) of which 614 (64.9%) were aphakic. 537 (36.2%) eyes underwent Boston KPro Type 1 as a primary procedure; defined as KPro implantation without prior corneal transplant procedure. Indications for Boston KPro Type 1 were diverse and frequently overlapping, reflecting the complex ocular histories of included patients; multiple graft failure and ocular surface injury were the most frequently reported indications. The range of prior grafts varied from 0 to 13 across 7 studies. A total of 11 studies explicitly reported a definition of glaucoma, which most commonly incorporated one or more of the following criteria: elevated or uncontrolled intraocular pressure, structural optic nerve changes (e.g., C/D ratio progression or nerve fiber layer thinning on optical coherence tomography [OCT]), and corresponding visual field changes characteristic of structural changes. A comprehensive summary of demographic and clinical characteristics is provided in Table 2 .

Table 2

Baseline Demographic and Clinical Characteristics of Eyes Undergoing Boston Keratoprosthesis Implantation.

Characteristic	Number (%)
Total eyes	1482
Total patients	1402
Age (SD)	54.5 (8.2)
Sex
Female	460 (32.8)
Male	790 (56.3)
NR	152 (10.9)
Lens status
Aphakic	614 (41.4)
Pseudophakic	332 (22.4)
Phakic	97 (6.6)
NR	439 (29.6)
Kpro type
Primary Kpro	537 (36.2)
Secondary Kpro	685 (46.2)
Repeat Kpro	19 (1.3)
NR	241 (16.3)
Indication
Multiple graft failure	348 (23.5)
Chemical/thermal burn	268 (18.1)
Corneal degeneration/endothelial disease	184 (12.4)
Limbal Stem Cell Deficiency	153 (10.3)
Infectious causes	90 (6.1)
Aniridia	62 (4.2)
Traumatic	54 (3.6)
Autoimmune	34 (2.3)
Other	289 (19.5)

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