Introduction:
In the recent times with advanced surgical techniques and instruments, it is possible to selectively replace only the dysfunctional layer/s of the cornea. Dr Charuta Puranik is highly skilled in all such lamellar surgical procedures with all the advantages of a corneal transplant but greatly reducing its side effects and long-term complications
DMEK is a partial-thickness cornea transplant procedure that involves selective removal of the patient’s Descemet membrane and endothelium, followed by transplantation of donor corneal endothelium and Descemet membrane without additional stromal tissue from the donor. The graft tissue is merely 10-15 microns thick. Similar to DSAEK, direct contact with the DMEK graft tissue is categorically avoided to prevent endothelial cell damage and graft failure.
Dr Charuta uses extremely thin donor tissue (just 5% of corneal thickness) and provides more patients with 20/20 or 20/25 than DSEK. In fact, DMEK provides 20/25 or better vision for about 3 out of 4 patients. Additionally, the risk of rejection is reduced with DMEK to less than 1 percent.
Descemet’s Membrane Endothelial Keratoplasty (DMEK) is long sought innovation in corneal transplantation that is in use only since recent times. With all of the advantages of its predecessor DSEK, DMEK can be done through even smaller incisions and visual recovery time is even faster. DMEK has even lower rates of transplant rejection (~2%). It is minimum access cornea surgery in the highest sense.
How is it done:
A clear corneal incision is created, the recipient endothelium and Descemet membrane are removed, and the graft is loaded into an inserter. After injecting the tissue into the anterior chamber, the surgeon orients and unscrolls the graft, and a bubble air is placed in the anterior chamber to support graft adherence.
Basic procedure steps:
Create two to four paracentesis sites.
Fill the anterior chamber with Healon.
Create an inferior peripheral iridotomy using a bent 30-gauge needle and Sinskey hook to prevent post-operative pupillary block.
Mark the recipient’s corneal epithelium with a circular ring slightly larger than the planned graft diameter to create a template for resection of the host tissue.
Score Descemet membrane peripherally using a reverse Terry-Sinskey hook, then peel Descemet membrane from the overlying stroma.
Create an incision temporally using a keratome, then remove the free Descemet membrane using forceps.
Remove the Healon using the irrigation/aspiration handpiece.
Inject Miochol to constrict the pupil and BSS to normalize the pressure.
Carefully lift the donor tissue by grasping the outermost edge with tying forceps and submerge it in trypan blue solution for 60 seconds to stain the tissue and make it more visible.
Place the tissue in a BSS-filled petri dish and it will scroll spontaneously. Aspirate it into a modified glass Jones tube.
Insert the tip of the glass tube into the clear corneal incision and inject the donor tissue into the anterior chamber.
Release fluid from a paracentesis to flatten the anterior chamber.
Gently tap and swipe on the anterior corneal surface until the graft is appropriately positioned and unscrolled.
Inject 20% SF6 into the anterior chamber to secure the graft and wait 10-15 minutes for adhesion.
Close the main incision with a 10-0 nylon suture.
Perform an air-fluid exchange to ensure there is no gas trapped behind the iris and assess for graft adhesion.
Injection another bubble of 20% SF6 to cover the graft, about 80-90% of the anterior chamber.
During DMEK, the patient’s existing poorly functional endothelium is removed and replaced with this specially prepared donor tissue. After the patient is prepped for the procedure and their diseased tissue is removed, the surgeon places the prepared donor tissue in a solution which changes it to a tinted blue colour temporarily so the surgeon can better see it. The tissue is then placed into an insertion device that is similar to a syringe. The syringe is inserted through the same small incision in the eye of the patient that was used for the removal of the diseased tissue and the new tissue is placed in the eye.
Once a DMEK graft is placed into the patient’s eye, it usually curls up into a scroll. The scroll has to be unrolled and the surgeon has to determine which side should face the recipient cornea and which side should face the inside of the eye. We have developed some techniques to help with this and the surgeon performs a test on the wake patient and asked if they can see a light before they continue to ensure the placement is correct. To unroll the scroll, the surgeon uses small puffs of air and a few surgical tools to ensure the tissue is correctly placed.
Finally, the surgeon ensures the amount of air is correct. This is an important step because the air is used to hold the tissue in the correct place. Too much air or not enough air can be problematic so it’s important to have the right amount. Lastly, the surgeon sutures the small opening that was made in the patient’s eye.
Why is it done:
The indications for DMEK are similar to those for DSAEK, including endothelial dystrophies (such as Fuchs corneal dystrophy and posterior polymorphous corneal dystrophy), pseudophakic bullous keratopathy, ICE syndrome, and other causes of corneal endothelial dysfunction. Most commonly in India Dr Charuta treats dysfunctional endothelium due to Cataract surgery.
Post Op care & instructions:
DMEK offers the most rapid visual rehabilitation of any keratoplasty technique to date. Final visual acuity can be outstanding due to minimal optical interface effects. Discontinuation of topical steroids can be considered at or before 1 year after the procedure, especially for patients with elevated intraocular pressure.
Typically, the patient is monitored for around two hours after surgery and this is permitted to go home or to the hotel to rest and will return the next day (post-op day 1) and the following (post-op day 2) for exams and finally on a 5th day after surgery which is when they are typically released to go home.
Risks & Complication:
Because less tissue is transplanted, there is a lower risk of allograft rejection and less long-term reliance on topical steroids compared with other types of keratoplasty.
Because of thinness, fragility, and its characteristic scrolling properties (with the endothelium facing outward), the donor tissue can be difficult to handle and contribute to technical difficulties with the procedure. There is a higher risk of graft edge lifts compared with DSAEK, sometimes requiring a re-bubble procedure.
The biggest challenge with DMEK is the preparation of the donor tissue. Basically, the endothelium and attached Descemet’s membrane has to be peeled off the back of the donor cornea. The ultra-thin DMEK grafts are so fragile that sometimes the precious donor tissue tears while separating the layers and it cannot be salvaged. Descemet’s membrane is only about 15 microns thick! So the preparation has to be done very carefully-this is the highest level of skill and we offer the same. Now a days ready made scrolls are also supplied by eye banks -however we don’t use them.