Learning curve has impact on graft detachment rate in DMEK, study finds

The number of functional grafts increased with surgical experience.

Thomas John

Corneal transplantation for endothelial failure has progressively moved from an approximately 550-µm full-thickness transplantation in penetrating keratoplasty to a 15-µm transplantation in endothelial keratoplasty, a 97% reduction in the amount of transplanted corneal tissue. In other words, with endothelial keratoplasty, there is retention of 97% of the patient’s cornea that may offer a biomechanically more stable cornea as compared with PK. From a real-world, daily perspective, it is comparable in thickness to food wrap or cling wrap (12.5 µm).

In this context, the term endothelial keratoplasty is used synonymously with Descemet’s membrane endothelial keratoplasty, the most advanced form of present-day posterior lamellar keratoplasty. This giant leap forward in corneal transplantation technique has restored the diseased cornea to an almost normal-appearing human cornea following a DMEK procedure, with quicker visual recovery and a full complement of improved visual quality as compared with PK. Such visual benefit to the patient is associated with technical difficulties for the surgeon, from donor tissue preparation without tearing the Descemet’s membrane followed by unrolling the thin membrane and attaching it with proper orientation to the inside stromal surface of the recipient cornea, preferably using a no-touch technique. It is therefore understandable that the surgeon has to go through a learning curve to minimize potential complications associated with the procedure.

In this column, Dr. Dapena describes progressively decreasing complications associated with DMEK as surgeon experience increases over time.

Thomas John, MD
OSN Surgical Maneuvers Editor

Isabel Dapena

The learning curve has a significant impact on the rate of graft detachment in Descemet’s membrane endothelial keratoplasty, according to a study by the medical team of Gerrit Melles, MD, who pioneered the technique.

“We have gradually learned that certain precautions like avoiding the use of viscoelastic substances or plastic vials during surgery, or avoiding the presence of posterior vitreous pressure during the operation, could minimize several complications,” Isabel Dapena, MD, said at a recent meeting.

The main difference between Descemet’s stripping endothelial keratoplasty and Descemet’s membrane endothelial keratoplasty (DMEK) is that in DSEK a posterior lamella composed of stroma, Descemet’s membrane and endothelium is transplanted, whereas DMEK uses an isolated Descemet’s membrane with only endothelium and no stroma attached to it.

In Melles’ technique, the diseased Descemet’s membrane is removed from the recipient by descemetorrhexis under air. The donor Descemet’s membrane, previously harvested at an eye bank, is injected as a roll inside the eye, carefully unfolded by indirect manipulation with balanced salt solution and air, and finally positioned against the stroma of the recipient cornea.

First series

The first series of 135 patients treated with DMEK at the Netherlands Institute for Innovative Ocular Surgery in Rotterdam was divided into three consecutive subgroups of 45 patients. The aim of the study was to compare best corrected visual acuity and endothelial density at 1, 3 and 6 months as well as intraoperative and postoperative complications and to determine the impact of the learning curve on these parameters.

A total of 110 patients were evaluated for visual acuity. Twenty-five were excluded due to lack of available data, low visual potential, or graft detachment or failure. For the same reasons, 28 patients were excluded from the evaluation of cell density.

“Clinical outcomes were similar in the three groups, with almost all patients achieving BCVA of 20/40 or better and nearly 75% achieving BCVA of 20/25 or better. Endothelial cell density (1,747 ± 527 cells/mm²) was also similar after 6 months,” Dr. Dapena said.

Further results

In some cases, superior acuity was achieved. Among them was a patient who underwent DMEK surgery in both eyes. The left eye was operated on earlier, as part of the first group of 45 patients. There were some wrinkles in the graft but they did not impair visual acuity. The patient achieved 20/16 BCVA in the left eye and 20/12 in the right eye.

Slit-lamp photographs of a cornea 6 months after initial DMEK (top), and 1 month after secondary DSEK (bottom). During DMEK surgery, complete unfolding of the Descemet’s graft proved difficult due to the presence of a shallow anterior chamber, as a result of vitreous pressure. In the upper quadrants, significant wrinkling of the graft (arrows) can be observed, limiting the BCVA to 20/40 (0.5). Because no spontaneous clearance was seen at 6 months, a secondary DSEK procedure was performed. Image: Dapena I

However, a significant difference was reported in the rate of complications, particularly graft detachment, among the three groups.

Graft detachment is the main complication in DMEK and is mainly correlated with intraoperative vitreous pressure (Figure), according to Dr. Dapena.

Complete or partial graft detachment occurred in nine cases (20%) in the first group, in six cases (13.3%) in the second group, and in two cases (4.4%) in the last group.

The need for secondary surgery also diminished over time. Re-bubbling was performed in five eyes in the first group, in two eyes in the second group and in one eye in the third group. Ten patients in the first group, five in the second and only one in the third needed secondary DSEK.

“With our standardized ‘no-touch’ technique, DMEK is becoming an easier procedure. However, a difference in learning curve-related outcomes was to be expected,” Dr. Dapena said. – by Michela Cimberle

References:

• Dapena I, Ham L, Droutsas K, van Dijk K, Moutsouris K, Melles GR. Learning curve in Descemet’s membrane endothelial keratoplasty: First series of 135 consecutive cases. Ophthalmology. 2011;118(11):2147-2154.
• Dirisamer M, Ham L, Dapena I, van Dijk K, Melles GR. Descemet membrane endothelial transfer: “Free-floating” donor Descemet implantation as a potential alternative to “keratoplasty” [published online ahead of print Dec. 2, 2011]. Cornea. doi:10.1097/ICO.0b013e31821c9afc.
• Guerra FP, Anshu A, Price MO, Price FW. Endothelial keratoplasty: fellow eyes comparison of Descemet stripping automated endothelial keratoplasty and Descemet membrane endothelial keratoplasty. Cornea. 2011;30(12):1382-1386.

• Isabel Dapena, MD, can be reached at NIIOS, H.A. Maaskantstraat 31, 3071 MJ Rotterdam, Netherlands; email: dapena@niios.com.
• Edited by Thomas John, MD, a clinical associate professor at Loyola University at Chicago and in private practice in Oak Brook, Tinley Park and Oak Lawn, IL. He can be reached at 708-429-2223; fax: 708-429-2226; e-mail: tjcornea@gmail.com.
• Disclosures: Drs. Dapena and John have no relevant financial disclosures.