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Pre-Descemet’s endothelial keratoplasty combines advantages of DSAEK, DMEK
The PDEK graft allows easy intraoperative handling because it is not as flimsy as Descemet’s membrane alone, and PDEK can use donor eyes of any age.
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Corneal transplantation for endothelial decompensation is shifting predominantly to endothelial keratoplasty. Descemet’s stripping automated endothelial keratoplasty has become popular, mainly because of the ability to procure prepared tissue from eye banks. Descemet’s membrane endothelial keratoplasty has specific advantages but is not yet widely practiced. Disadvantages of DSAEK include interface haze, hyperopization and difficult graft preparation, and disadvantages of DMEK include difficult graft preparation, challenging nature of surgery and inability to harvest grafts from young donor corneas.
We describe a new technique called pre-Descemet’s endothelial keratoplasty (PDEK), which combines many of the advantages of DSAEK and DMEK while avoiding their many individual disadvantages (Figures 1 to 3). This work was done in collaboration with Harminder Dua, MD, PhD, FRCS, FRCOphth, from the United Kingdom.
Figure 1. Preparation of PDEK graft. A: A 30-gauge needle connected to a syringe with air enters the cornea from the edge of the sclera. The donor cornea is kept endothelial side up. B: The needle is gradually passed to the center of the cornea, taking care not to perforate the endothelial side. Once it reaches the center of the cornea, air is injected into the corneal layers. C: A type 1 big bubble is formed. The air is now between the pre-Descemet’s layer and stroma. Note the big bubble does not reach the periphery of the cornea because there are firm adhesions between the pre-Descemet’s and stroma in the periphery. If a bubble is created to the edge of the cornea, it is a type 2 big bubble. This means the air has formed between the Descemet’s membrane and the pre-Descemet’s layer. If a type 2 big bubble forms, one cannot do PDEK and will have to do DMEK. D: Trypan blue is injected into the type 1 big bubble as the bubble has been perforated. This helps to stain the tissue and also helps the surgeon get a clear view of the lenticule. E: A trephine is taken, matching the size of the type 1 big bubble and trephination done. F: Any area that has not been clearly cut is cut with Vannas scissor, and the entire lenticule is lifted. This graft now contains endothelium, Descemet’s membrane and pre-Descemet’s layer.
Images: Agarwal A, Jacob S
Figure 2. Steps for PDEK. A: Preop photo of pseudophakic bulbous keratopathy. B: After marking the cornea with a trephine, Descemet’s membrane is scored and stripped. C: Pupilloplasty is done. D: Pupilloplasty is completed. Pupil is now round. E: The PDEK graft is injected into the anterior chamber with the help of the injector. F: The graft is unrolled once correct orientation is checked. Air is injected under the graft to fix it to the cornea. PDEK graft is attached. Air is filling the anterior chamber.
Figure 3. Postop photo of a case of Fuchs’ dystrophy. PDEK cataract IOL was done. One month postop, vision was 20/20.
Technique
Air separation of a DMEK graft was reported earlier by Busin et al, and Jafarinasab et al reported additional tissue as “residual stroma” attached to Descemet’s membrane when separation is caused with an injection of air in deep anterior lamellar keratoplasty. A distinct pre-Descemet’s layer of tissue, the Dua’s layer, was described in 2007. Unlike in DMEK, in which only the Descemet’s membrane and donor endothelium are transplanted, PDEK additionally includes the pre-Descemet’s layer in the graft.
The PDEK graft is prepared by air separation. When air is slowly injected with a 30-gauge needle attached to a 5 mL syringe inserted from the limbus into superficial mid-peripheral stroma, it can form either a type 1 or type 2 big bubble. A type 1 big bubble is a PDEK graft. It is a well-circumscribed, central dome-shaped elevation measuring 7 mm to 8.5 mm in diameter. It always starts in the center and enlarges centrifugally, retaining a circular configuration. A type 2 big bubble is a DMEK graft. It is larger, up to 10.5 mm, and extends from the periphery. The bursting pressure of the PDEK graft is higher than that of the DMEK graft. The type 2 bubble collapses on attempting to peel the Descemet’s membrane off whereas it can be peeled off a type 1 bubble without the bubble collapsing, proving the inclusion of the pre-Descemet’s layer in the PDEK graft. Sometimes, a combination of a type 1 and type 2 bubble may be obtained. The pre-Descemet’s layer provides additional splintage and makes the graft more robust and resistant to tears.
Creation of a type 1 big bubble is similar to an Anwar’s big bubble created for DALK except that air is injected from the endothelial side. Once a type 1 bubble is obtained, further expansion may be done with viscoelastic.
Harvesting the PDEK graft is easy and can be done in donor corneas of any age. After achieving a type 1 big bubble, the donor graft is trephined along the margins of the bubble. The bubble is pierced at the extreme periphery, and trypan blue injected into the bubble to stain the graft. The PDEK graft is then cut around the trephine mark with a pair of Vannas scissors and placed in the tissue culture medium. The final size of the graft after cutting may be slightly larger than the trephine. The graft is loaded into an injector when ready for insertion.
Once the donor is prepared, the rest of the surgery is similar to that of DMEK. The epithelium may be removed for better visualization. A blunt trephine is used to mark an area 0.5 mm larger than the graft size. The anterior chamber is entered, and the host Descemet’s membrane is scored, stripped and removed. The injector is then prepared by removing the spring. The PDEK graft is stained and loaded facing upward into a cartridge. The graft is then injected into the anterior chamber. The incision is sutured, and graft orientation is confirmed. It is unrolled using short bursts of fluid as well as by flicking the corneal surface. The graft is then centered and air injected under the graft to float it up against the overlying stroma.
E-PDEK
Endoilluminator-assisted DMEK (E-DMEK), which we described previously, can be translated into PDEK surgery as endoilluminator-assisted PDEK (E-PDEK). E-DMEK or E-PDEK achieves excellent visibility even through hazy corneas and allows better three-dimensional comprehension of graft morphology, orientation and dynamics as well as enhanced depth perception.
Conclusion
In our experience, the PDEK graft, with its relative rigidity and toughness, allows easy intraoperative handling and insertion of the tissue because it is not as flimsy as and does not tear as easily as Descemet’s membrane alone.
References:
Busin M, et al. Ophthalmology. 2010;doi:10.1016/j.ophtha.2009.12.040.Jafarinasab MR, et al. Cornea. 2010;doi:10.1097/ICO.0b013e3181ba7016.
For more information:
Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; fax: 91-44-28115871; email: dragarwal@vsnl.com; website: www.dragarwal.com.Disclosure: No products or companies that would require financial disclosure are mentioned in this article.