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Stepwise approach ideal for pre-Descemet’s endothelial keratoplasty
Donor graft preparation is the most important stage of the PDEK process.
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Endothelial keratoplasty has revolutionized the surgical approach for corneal endothelial disorders that are normally not well managed with a medical line of treatment and often necessitate a surgical approach.
Pre-Descemet’s endothelial keratoplasty (PDEK) is a newer option among the variants of endothelial keratoplasty; it essentially requires the transplantation of the pre-Descemet’s layer in association with the Descemet’s membrane-endothelium complex. OCT studies have demonstrated the thickness of the PDEK donor graft to be approximately 30 µm to 35 µm with both adult and infant donor tissue. The addition of the pre-Descemet’s layer to the Descemet’s membrane-endothelium complex acts as a splint that provides better support and tissue unrolling of the donor graft in the recipient’s eye.
Donor graft preparation
Donor graft preparation is the most important part of the PDEK procedure. Formation of a type 1 bubble is essential and involves the separation of the pre-Descemet’s layer with the Descemet’s membrane-endothelium complex from the residual stroma. This is unlike a Descemet’s membrane endothelial keratoplasty procedure, which involves the formation of a type 2 bubble with the passage of air in between the pre-Descemet’s layer and the Descemet’s membrane-endothelial complex and leads to the harvesting of only the Descemet’s membrane-endothelial layer, leaving the pre-Descemet’s layer attached behind in the donor graft.
A mixed type 1 and type 2 bubble is often created during the procedure of air dissection. At this stage, the surgeon needs to be careful so as to avoid any rupture of the bubble, along with dissection of the bubble along the correct plane because harvesting a type 2 graft would lead to abandonment of PDEK; the surgeon would then need to perform a DMEK procedure.
A donor graft with a corneoscleral rim is held with the endothelial side up. A 30-gauge needle attached to an air-filled 5-mL syringe is introduced from the periphery of the graft up to the center, and air is injected. A type 1 bubble, around 8 mm in diameter, is formed and characteristically spreads from the center to the periphery. The edge of the bubble is entered with a side-port blade, and trypan blue is injected inside to stain the graft. The graft is cut with corneoscleral scissors all around the periphery of the bubble, and it is placed in storage media (Figures 1a to 1f).
Images: Agarwal A, Narang P
Figure 2. T-ACM is introduced into the eye.
Figure 3. T-ACM is connected to the air pump.
Figure 4. Side-port incision is framed.
Figure 5. Descemetorhexis is performed with a reverse Sinskey hook.
Figure 6. Clear corneal incision is framed.
Figure 7. Iridectomy is performed with a vitrectomy probe.
Figure 8. PDEK graft is loaded into the cartridge of the foldable IOL.
Figure 9. The air pump is switched off.
Figure 10. PDEK graft is injected into the anterior chamber.
Figure 11. Corneal incision is sutured to seal the anterior chamber.
Figure 12. Correct orientation of the graft is checked with an endoilluminator.
Figure 13. The graft is unrolled, and air is injected beneath the graft.
Figure 14. Air pump is switched on, and the anterior chamber is filled with air to facilitate further adhesion of the graft to the endothelial surface.
Figure 15. The graft is centered.
15-step process
This procedure can be summarized in 15 steps that need to be followed sequentially.
Step 1: Fix the trocar anterior chamber maintainer (T-ACM; Figure 2), or a routine anterior chamber maintainer can also be fixed if the surgeon is not well versed with the use of a T-ACM. Fixing up an infusion set-up allows the surgeon to easily switch over between an air-fluid infusion when required during the surgical procedure.
Step 2: Connect the T-ACM to an air pump (Figure 3). This facilitates continuous air infusion into the eye and helps to perform the procedure with an anterior chamber that is always well formed.
Step 3: Two side-port incisions are made at the superotemporal and superonasal position (Figure 4). This is done so as to allow these sites to be utilized in the future for further intraocular manipulation.
Step 4: Descemetorhexis is performed with a reverse Sinskey hook (Figure 5). This step is essentially the same as in a DMEK procedure.
Step 5: A 2.8-mm clear corneal incision is made, and the scored Descemet’s membrane-endothelium complex is removed (Figure 6). This site further allows the introduction of the graft into the eye.
Step 6: Inferior iridectomy is performed with a vitrector (Figure 7). This helps to prevent any incidence of pupillary blockage.
Step 7: Load the PDEK graft in the cartridge of the foldable IOL (Figure 8, which was originally described by Francis Price).
Step 8: Switch off the air pump (Figure 9). This step is performed before the graft is injected so that the force of the air does not displace the graft, and it also ensures that there is enough room for the graft to enter and be properly placed into the anterior chamber.
Step 9: Inject the PDEK graft in the anterior chamber (Figure 10). If the anterior chamber is shallow, then the assistant can inject a bit of fluid into the chamber from the side-port incision.
Step 10: Suture the clear corneal incision (Figure 11). This ensures that there is no wound leakage and that the graft is placed in a well-formed anterior chamber.
Step 11: The correct orientation of the graft is checked (Figure 12). An endoilluminator can be used to facilitate this.
Step 12: Unroll the graft and inject a bit of air beneath it (Figure 13).
Step 13: Switch on the air pump connected to the T-ACM. This pushes the graft and helps it to adhere with the corneal surface (Figure 14).
Step 14: Fully unroll the graft using a reverse Sinskey hook and center it properly (Figure 15). Corneal massage is performed to adjust the center position of the donor graft and to eliminate residual fluid at the donor graft-recipient interface. Residual interface fluid can also be drained through corneal venting incisions.
Step 15: Suture the wounds and remove the T-ACM.
After the surgical procedure is completed, the patient is made to lie in the supine position for 2 hours or so and is allowed minimal movements for the next 24 hours. The postoperative regimen comprises antibiotics and steroid drops that are slowly tapered over a period of 3 months. Figure 16 demonstrates the preoperative and postoperative images of the patient and showcases complete clearance of the corneal haze.
The advantage of a PDEK procedure is that it increases the pool of donor grafts for endothelial keratoplasty because it allows the use of infant donor tissue, unlike a DMEK procedure in which only donors older than 40 years of age are advocated. Another advantage is that PDEK allows endothelial keratoplasty to be done with a minimal amount of pre-Descemet’s layer attached to the donor tissue as compared with ultrathin Descemet’s stripping endothelial keratoplasty or Descemet’s stripping automated endothelial keratoplasty, which requires the use of expensive instruments such as a microkeratome to harvest the donor tissue.
- 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; email: dragarwal@vsnl.com; website: www.dragarwal.com.
- Priya Narang, MS, is the director of Narang Eye Care & Laser Centre, Ahmedabad, India. She can be reached at email: narangpriya19@gmail.com.
Disclosures: Agarwal and Narang report no relevant financial disclosures.