Graft Preparation

Harvesting of the DM graft was performed as previously described. In short, corneoscleral buttons from donor globes were obtained post mortem and stored in organ culture medium (31°C). In the eye bank, endothelial cell morphology and viability were evaluated and the corneoscleral buttons were mounted endothelial side up on a custom-made holder, so that a 9.5-mm-diameter DM sheet with its endothelium could be stripped off from the posterior stroma. Harvested “Descemet rolls” were then stored in organ culture medium until the day of transplantation.

Surgery

A circular 9.0-mm-diameter “descemetorrhexis” was performed under air, by scoring and stripping off the DM from the posterior stroma with a reversed Sinskey hook (DORC International, Zuidland, The Netherlands). The donor Descemet roll was stained (0.06% trypan blue solution; VisionBlue; DORC International), sucked into a custom-made injector (DMEK-inserter; DORC International) and injected through a 3.0-mm limbal tunnel incision into the recipient anterior chamber. The graft was oriented with the endothelial side facing the recipient iris and donor DM facing recipient stroma. After complete graft unfolding over the iris, an air bubble was injected underneath the graft to attach and fixate it onto the recipient posterior stroma. The anterior chamber was then completely filled with air for 60 minutes, followed by an air-liquid exchange, leaving a 30%–50% air bubble.

Postoperative medication included topical antibiotics for 2 weeks and a steroid regimen of dexamethasone 0.1% drops 4 times daily for 4 weeks, followed by fluorometholone drops 4 times daily, tapered to once daily until 1 year postoperatively and thereafter once daily or once every other day.

Data Collection and Analysis

All of the 250 eyes included in our study potentially had a follow-up of at least 4 years; 171 eyes, of 5 years; 87 eyes, of 6 years; and 32 eyes, a follow-up of 7 years after DMEK ( Table 2 ). Recipient eyes were examined before surgery and postoperatively at 6 months, at 1 year, and yearly thereafter. Pre- and postoperative best-corrected visual acuity (BCVA), ECD, and central corneal thickness (CCT) were measured using the Snellen visual acuity chart, noncontact autofocus specular microscopy (Topcon SP3000p; Topcon Medical Europe BV, Capelle a/d IJssel, The Netherlands), and Scheimpflug imaging (Pentacam HR; Oculus GmbH, Wetzlar, Germany), respectively. Postoperative complications were recorded in a database. Anterior segment optical coherence tomography (AS-OCT; Heidelberg Slit-Lamp OCT; Heidelberg Engineering GmbH, Heidelberg, Germany) was performed to evaluate graft adhesion status. Partial graft detachment greater than one third of the graft surface area was considered a “major” detachment. Partial detachment of less than or equal to one third of the graft surface area was considered a “minor” detachment.

Endothelial graft failure was diagnosed with slit-lamp biomicroscopy (Topcon Medical Europe BV, Capelle a/d IJssel, The Netherlands), revealing corneal edema that necessitated repeat keratoplasty. Primary graft failure (PGF) was defined as the absence of corneal clearance after surgery despite full graft attachment and secondary graft failure (SGF) as a corneal decompensation due to donor endothelial failure after a postoperative interval with a clear cornea in an attached graft or in the presence of a minor graft detachment.

For BCVA analysis only cases with low visual potential owing to concomitant ocular pathology (retina or optic nerve disorders) were excluded, but not eyes with a graft detachment ( Table 2 ). For statistical analysis, BCVA values were converted to logarithm of the minimum angle of resolution (logMAR) units. Linear mixed models were used to evaluate how BCVA, ECD, and CCT values change over time after DMEK, while correcting for the covariates patient age, patient sex, lens status, and surgery indication. Sensitivity analyses were carried out to check whether the results were influenced by eyes with a major detachment, by the first 25 eyes operated (the learning curve), and by the inclusion of the second operated eye for some patients (n = 41). Survival analysis comprised 246 eyes (4 eyes had no follow-up information). A life table and a Kaplan-Meier curve display the graft survival probabilities. All multiple tests were controlled for false discovery rate and, as a result, all reported P values are corrected P values, which can be interpreted by comparing them directly with the significance level of .05. All analyses were performed with R.

Visual Rehabilitation

At 4 years after DMEK, 96% of eyes reached a BCVA of ≥20/40 (≥0.5), 83% reached ≥20/25 (≥0.8), 54% ≥20/20 (≥1.0), and 22% ≥20/17 (≥1.2) ( Figure 1 , Top). From 5 to 7 years, these values were roughly similar ( Figure 1 , Top). The results of the linear mixed model showed that compared with preoperative values, BCVA (logMAR) improved significantly within the first 6 months after surgery (mean = −0.40, standard error [SE] = 0.02, P < .0001). From 6 months up to 7 years postoperatively BCVA remained stable (mean = −0.04, SE = 0.05, P = .7114). Sensitivity analysis showed that excluding eyes with a major graft detachment (n = 20) does not change the stabilization time point (6 months follow-up), but without these eyes the average improvement until 6 months follow-up would be even higher (mean = −0.45, SE = 0.02, P < .0001). Two covariates were significantly associated with BCVA outcomes: patient age ( P = .0016) and surgery indication. Fuchs endothelial dystrophy eyes have significantly better BCVA outcome compared with BK eyes, on average 0.13 points on the logMAR scale (SE = 0.04, P = .0016).

Clinical outcome up to 7 years after Descemet membrane endothelial keratoplasty (DMEK). (Top) Bar graph displaying the best-corrected visual acuity (BCVA) after DMEK at different follow-up intervals up to 7 years. (Middle) Graph displaying the mean endothelial cell density (ECD) after DMEK up to 7 years. ECD decrease compared with preoperative ECD are shown in bold and additional ECD decrease compared with the previous follow-up are shown in italics. (Bottom) Graph displaying the mean central corneal thickness (CCT) after DMEK up to 7 years. CCT decrease compared with preoperative CCT are shown in bold and additional CCT decrease compared with the previous follow-up are shown in italics.

Endothelial Cell Density

Donor ECD decreased from 2553 (±194) cells/mm ² before surgery (n = 249) to 1687 (±521) cells/mm ² at 6 months (n = 206), 1593 (±520) cells/mm ² at 1 year (n = 193), and 1210 (±492) cells/mm ² at 4 years (n = 154). At 6 years, ECD averaged 1037 (±429) cells/mm ² (n = 49) and at 7 years, 903 (±429) cells/mm ² (n = 17) ( Figure 1 , Middle). Hence, compared with preoperative values, ECD decreased by 33.9% within the first 6 months, by 37.6% at 1 year, and by 52.6% at 4 years. Compared with the previous follow-up, ECD decreased significantly at 6 months ( P < .0001). From 1 year on, a relatively “stable” average yearly ECD decrease of 9% was observed ( Figure 1 , Middle). None of the covariates was significantly associated with ECD decrease.

Central Corneal Thickness

CCT decreased by 21.4%, from 670 (±93) μm before surgery (n = 190) to 527 (±51) μm at 6 months (n = 189), 529 (±38) μm at 1 year (n = 188), 536 (±36) μm at 4 years (n = 142), and 550 (±51) μm at 7 years (n = 16). Compared with preoperative values, CCT decreased significantly at 6 months ( P < .0001). After the first 6 months, no change was found up to 7 years ( P = .8447) ( Figure 1 , Bottom). Covariates patient age ( P = .0005) and lens status ( P = .0047) were related to changes in CCT over time.

Complications

Of all postoperative complications (predominantly partial graft detachment), 88% (73/83) occurred within the first 6 months after surgery ( Table 3 , Figure 2 ). After 6 months, the remaining 12% (10/83) of complications were limited to secondary graft failure and allograft rejection episodes. Secondary graft failure occurred in 2% (5/250) of eyes and was attributed to endothelial failure in the presence of a minor graft detachment (1 eye), after a successful rebubbling procedure (1 eye), and after rejection (3 eyes of 2 patients). All secondary graft failures occurred after the 1-year follow-up, at various time points throughout the 7-year follow-up period ( Figure 2 , Table 3 ).

Table 3

Complications and Repeat Interventions in 250 Eyes up to 7 Years After Descemet Membrane Endothelial Keratoplasty

Complications	Occurrence		Time Interval of Occurrence				Resulting in Repeat Transplantation
			Short-term, N	Longer-term, N
	%	n	≤6 Months	6 Months–1 Year	1–2 Years	2–7 Years
Primary graft failure	1.6%	4	4				4
Secondary graft failure	2.0%	5	0		2	3	5
Minor detachment ≤1/3	11.6%	29	29				[1] a
Major detachment >1/3	15.6%	39	39				29 + [1] a
Allograft rejection episode	2.4%	6	1	1	1	3	[3] a
Reinterventions
Rebubbling (successful)	4.4%	11	11 (5)				[6] b + [1] c
Secondary DSEK	9.6%	24	17	7	–	–
Repeat DMEK	5.6%	14	1	5	3	5

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