EyeWorld Asia-Pacific March 2018 Issue

March 2018 EWAP FEATURE 15 cut edges are again stained with trypan blue, and the peeling is completed. It is recommended to start practicing DMEK graft prepara- tion in the wet lab. Ask for practice corneas that are from donors 55 years or older with no history of diabetes. Also, feel how Descemet’s membrane behaves, and note the amount of tension it can withstand before tearing. This is what makes DMEK preparation appealing. No special instruments are required other than a few trephine punches and the microfinger instrument. With our technique, we are able to prepare DMEK tissue safely and successfully most of the time. Mohit Parekh, PhD, research scientist, Veneto Eye Bank Foundation, Venice, Italy, and Massimo Busin, MD, Department of Ophthalmology, Villa Igea Hospital, Forli, Italy 1. The endothelial cell density (ECD) and mortality is checked before issuing the human donor cornea for transplantation. An ECD of >2,200 cells/mm 2 with <2% mortality is considered suit able in our eye bank for DMEK. 2. We use a SCUBA technique with minor modifications as described below. 3. The tissue is fixed on a suction block by creating vacuum with endothelial side facing upward. 4. A donor trephine (9.5 mm) is gently tapped on the endothelial surface to obtain a superficial cut. 5. The cut margins are made visible after staining it with trypan blue (0.25%). The stain is washed off with phosphate buffered saline (PBS). 6. The peripheral endothelium is removed, and the tissue is restained to differentiate between the remaining central endothelium and the bare stroma left after the excision of the peripheral endothelium. 7. A small drop of tissue culture medium is added topically on the endothelium to keep the cells moist while stripping. 8. A cleavage hook is used to iden- tify the plane of cleavage (moved radially along 360-degree cir- cumference), slightly detaching the DMEK graft at the periphery. 9. An anatomic forceps with 1.2- mm pointed tips is used to peel the tissue from the superior side toward the inferior. This step can be performed as a single peel method or a quadrant method depending on the attachment of the Descemet’s membrane to stroma. If the tissue is tightly attached, it can be peeled using a quadrant method or oscillating fashion (gently moving from right to left detaching the graft, followed by peeling). 10. The DMEK tissue is peeled 80% to 90%, leaving a small hinge. It is not repositioned back on the cornea. 11. A small (2.0 mm) skin biopsy punch is used to trephine the stroma. The peeled DMEK tissue is then repositioned back on the cornea by sterile sponges to reverse the flow of liquid and open the DMEK tissue on the cornea. 12. Vacuum is released, and the entire corneal tissue is inverted with the epithelial side facing upward. 13. The punched stromal part is removed, exposing the bare DM resting on the stroma. 14. The cleavage hook tip is colored with a skin marker, and a letter “F” is marked on the DM. 15. The punched stromal part is placed back on the cornea. 16. Trypan blue stain is applied on the top of the endothelial cells for 20 seconds and washed briefly with PBS. 17. The corneal tissue is placed in sucrose (hypotonic solution, 1.8%) for evaluation and meas- urement of ECD, morphology, and trypan blue positive cells. 18. The tissue is fixed using a cor- neal claw and stored in the transport medium for shipment. At the Veneto Eye Bank Foun- dation, we have pre-stripped 527 DMEK tissues since May 2014. Fewer than 1% of trypan blue positive cells have been observed; there has been a tissue wastage of less than 6%, including central or peripheral tears, total Descemet’s membrane detachment, and strong attachment. The low wastage rate and good quality of the grafts have prompted us to use this technique. Complicated tissues like donors with history of severe diabetes, horseshoe shaped tears, and previ- ous cataract interventions can be managed with this technique. 1 Mauricio Perez, MD, Santiago, Chile I was introduced to DMEK tissue preparation by my former preceptor, Clinical image of DMEK surgery with 20/20 vision 6 days after the surgery with residual gas bubble still seen Source: Mark A. Terry, MD continued on page 16