Graft Registry

Data for this prospective multicenter registry study was obtained from the Netherlands Organ Transplantation Registry (NOTR), a prospective national database founded by the Netherlands Transplantation Foundation (Nederlandse Transplantatie Stichting [NTS], http://www.transplantatiestichting.nl/over-de-nts ). Informed consent was obtained from patients to participate in the registry and for use of anonymized data for research purposes. Institutional review board approval for data extraction and analysis was provided by the NOTR scientific council. Data were anonymized prior to analysis and the study was performed in accordance with the tenets of the Declaration of Helsinki and Dutch legislation.

Population

The study cohort included all consecutive primary endothelial and penetrating keratoplasties performed in the Netherlands for the treatment of FED or PBK between January 1, 1998 and December 31, 2013. No other inclusion or exclusion criteria were applied. The term EK was used regardless of donor corneal dissection technique, including Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet stripping endothelial keratoplasty (DSEK).

Data Collection

In the Netherlands, donor corneas are allocated centrally and the allocation process is always registered in NOTR. NTS prospectively collects data on the recipient, donor, eye bank processing, surgical procedure, and follow-up with regular intervals using a standardized electronic data capture system. Data collection continues until graft failure or loss to follow-up ( http://www.transplantatiestichting.nl/professionals/cijfers-voor-professionals-1/transplantatie-follow ). Overall registry data capture during the study period was 89%. Overall lost to follow-up (LTFU) between 1998 and 2014 measured 19% for EK and 31% for PK, P < .001. LTFU after introduction of EK into standard care in 2007 measured 19% for EK and 16% for PK, P = .13.

Outcome Measures

The primary outcome measure of this study was graft survival, with a maximum follow-up duration of 5 years. Grafts were identified as failed when either a reason for graft failure was documented by the treating surgeon or a subsequent record for corneal retransplantation in the same eye was identified in the registry. Graft failure occurring within 3 months of transplantation was defined as primary graft failure (PGF). For failed grafts, interval to graft failure was defined by the duration between transplantation and recorded graft failure. For surviving grafts, censuring was performed at the last recorded visit. All patients with follow-up durations longer than 5 years were censored at the 5-year time point. Secondary outcome measures included best-corrected visual acuity (BCVA), spherical equivalent (SEQ), refractive astigmatism, and ECD. BCVA was defined as Snellen acuity in the grafted eye measured using either spectacles or contact lens. The best visual acuity was noted. Snellen BCVA was converted to logarithm of the minimal angle of resolution (logMAR) for statistical analysis. SEQ was defined as the sum of the spherical value and half the cylindrical value.

Statistical Methods

All statistical procedures were performed using SPSS software version 22.0 (SPSS Inc, Chicago, Illinois, USA). Baseline characteristics were reported as mean ± standard deviation (SD), median, and interquartile range (IQR) or frequencies and percentages, as appropriate. Baseline demographics were compared using a Student t test for numerical variables or χ ² test for categorical variables. Kaplan-Meier curves and Cox regression analysis were used to assess graft survival time. Transplantation indication was used as stratification variable. Linear mixed models (LMM) were fitted to investigate postoperative BCVA, SEQ, refractive astigmatism, and ECD over time. These dependent variables were reported as estimated marginal means for the combination of transplantation techniques (ie, EK and PK) and follow-up time points, evaluated at the means of the baseline of the dependent. Transplantation techniques, dependent variable at baseline, follow-up time points, and all interactions were included in the model as fixed variables; patient was included as a random variable; follow-up time points were taken as categorical variable. The level of statistical significance was set at .05 for all analyses.

Demographics

Recipient and donor demographics, indication for surgery, surgical procedure, and follow-up duration are given in Table 1 . Demographics did not differ between patients undergoing EK or PK for FED or PBK, respectively. Follow-up duration was shorter for EK than for PK for both indications.

Keratoplasty Practice Patterns and Indications

The total number of corneal transplantations performed annually for FED and PBK remained constant between 1998 and 2007. Between 2007 and 2014, the total number of corneal transplantations increased owing to an increase in the number of transplantations performed for FED ( Figure 1 , Top). A coinciding increase in the number of EK procedures and decrease in the number of PK procedures for both indications was observed ( Figure 1 , Bottom). The level of visual limitation at which EK was performed for the treatment of FED decreased significantly between 2006 and 2014 (β = −0.02 logMAR/year, P < .001) while remaining unchanged for PBK (−0.01 logMAR/year, P = .78). The age at which EK was performed did not decrease between 2008 and 2014 for either FED (0.09/year, P = .38) or PBK (−0.46/year, P = .19). Improvement of vision was the main indication for keratoplasty (FED: 95%, PBK: 77%), followed by combined pain reduction and visual improvement (FED: 4.5%, PBK: 16%) and pain reduction only (FED: 0.5%, PBK: 7%).

Practice patterns of corneal transplantation in the Netherlands. Total number of corneal transplantations performed annually for FED (blue) and PBK (green) in the Netherlands (Top). Total number of endothelial and penetrating keratoplasties performed for FED (green and blue, respectively) and PBK (purple and yellow, respectively) in the Netherlands (Bottom). FED = Fuchs endothelial dystrophy; PBK = pseudophakic bullous keratopathy.

Graft Survival

During the first 2 years of follow-up, graft survival was significantly lower following EK compared with PK for FED (95.2% vs 97.4%, hazard ratio [HR] = 1.99 [95% confidence interval (CI): 1.38–2.88], P < .001) and PBK (88.7% vs 94.5%, HR = 2.29 [95% CI: 1.47–3.56], P < .001). The Supplementary Figure (Top left) shows 2-year EK and PK graft survival for FED and PBK (Supplemental Material available at AJO.com ). PGF accounted for 27% and 33% of total EK graft failures and 2% and 3% of total PK graft failures for FED and PBK, respectively. Between 2 and 5 years of follow-up, graft survival was significantly better following EK compared with PK for FED (98.2% vs 95.2, HR = 0.58 [95% CI: 0.36–0.91], P = .019) and PBK (97.2% vs 85.9%, HR = 0.27 [95% CI: 0.10–0.72], P = .009). The Supplementary Figure (Top right) shows 2- to 5-year EK and PK graft survival for FED and PBK. The hazard ratio for EK vs PK decreased over time, dropping below 1 at 15 months of follow-up for FED and PBK. At 5 years follow-up, Cox regression analysis showed no difference in graft survival between EK and PK for FED (94.1% vs 93.3%, HR = 1.23 [95% CI: 0.95–1.60], P = .12) or PBK (87.3% vs 84.1%, HR = 1.18 [95% CI: 0.82–1.71], P = .37). Five-year graft survival was significantly better for FED compared with PBK for EK (94.1% vs 87.3%, HR = 2.29 [95% CI: 1.59–3.30], P < .001) and PK (93.3% vs 84.1%, HR = 2.92 [95% CI: 2.26–3.77], P < .001). Figure 2 (Top left) shows 5-year EK and PK graft survival for FED and PBK. Finally, 5-year graft survival following EK significantly improved over time for both FED (range = 82.0%–96.6%, HR = 0.67 [95% CI: 0.56–0.80], P < .001) and PBK (range = 74.2%–93.4%, HR = 0.71 [95% CI: 0.53–0.95], P = .022) while remaining stable following PK for the treatment of FED (range = 87.1%–92.5%, HR = 1.33 [95% CI: 0.95–1.87], P = .10) and PBK (range = 77.7%–92.6%, HR = 1.01 [95% CI: 0.77–1.32], P = .95).

Endothelial and penetrating keratoplasty graft survival. Five-year graft survival following endothelial keratoplasty (green) and penetrating keratoplasty (blue) for Fuchs endothelial dystrophy (Top left) and pseudophakic bullous keratopathy (Top right). The 2-year cutoff point in graft survival is shown in purple. Evolution of graft survival over time stratified by 2-year intervals for date of surgery following endothelial keratoplasty for Fuchs endothelial dystrophy (Bottom left) and pseudophakic bullous keratopathy (Bottom right).

The evolution of EK graft survival for FED and PBK over time, stratified by 2-year intervals for date of surgery, is shown in Figure 2 (Top right), demonstrating that more recently performed endothelial grafts show better survival.

Best-Corrected Visual Acuity

BCVA following EK and PK for FED and PBK is given in Table 2 . Preoperatively, BCVA was better in patients undergoing EK compared to PK for FED (0.68 ± 0.43 vs. 0.90 ± 0.52 logMAR, P < 0.001) and PBK (1.32 ± 0.65 vs. 1.60 ± 0.62 logMAR, P < 0.001). Correcting for preoperative differences in BCVA, postoperative BCVA was significantly better following EK compared to PK for the treatment of FED until 36 months of follow-up. Thereafter, BCVA remained better in the EK group, but did not reach statistical significance. Correcting for preoperative differences in BCVA, postoperative BCVA was significantly better following EK compared with PK for the treatment of PBK throughout the entire follow-up.

Refractive Outcomes

Refractive astigmatism and SEQ are given in Table 3 . Correcting for preoperative differences, postoperative SEQ and refractive astigmatism were significantly higher following PK compared with EK throughout the entire follow-up. Refractive shift is shown in Table 4 . Following EK, a significant hyperopic refractive shift measuring 0.34–0.67 diopter was observed throughout the entire follow-up.

Table 4

Dutch National Registry Study of Endothelial Versus Penetrating Keratoplasty: Refractive Shift

Follow-up	Endothelial Keratoplasty			Penetrating Keratoplasty
	N	Refractive Shift	P	N	Refractive Shift	P
3 months	1956	0.67	<.001	532	−0.63	.001
6 months	1849	0.57	<.001	1076	−0.78	<.001
12 months	1476	0.57	<.001	1108	−1.16	<.001
24 months	822	0.57	<.001	822	−1.89	<.001
36 months	505	0.45	<.001	647	−2.00	<.001
60 months	164	0.34	.026	449	−2.24	<.001

Refractive shift (diopter) following endothelial and penetrating keratoplasty corrected for baseline differences (linear mixed-model estimated marginal means).

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