Descemet Stripping Endothelial Keratoplasty
Descemet’s Stripping Endothelial Keratoplasty (DSEK)
Corneal transplantation is a widely practiced surgical procedure. Over the past decade, lamellar techniques have been developed to replace penetrating keratoplasty (PK)  . Endothelial Keratoplasty (EK) has been adapted as an alternative in the treatment of corneal endothelial disorders.  In the various forms of endokeratoplasty, Descemet’s membrane and the endothelium are replaced, with or without a varying amount of corneal stroma. 
In Descemet’s stripping endothelial keratoplasty (DSEK), the patient’s Descemet membrane is peeled off, using specially designed strippers  and replaced with a partial thickness graft: a transplanted disc of Posterior Stroma, Descemet and Endothelium (10-30 % of the inner donor cornea). Both donor and host cornea are manually dissected. Differently, in Descemet’s stripping automated endothelial keratoplasty (DSAEK) the donor dissection is carried out using a mechanical microkeratome. DSAEK is described as the procedure of choice for corneal endothelial failure in many centers. 
DSEK is intended to transplant a healthy endothelial cell layer that will pump the fluid out of the cornea. It’s expected to restore corneal clarity and improve vision.  This procedure corrects corneal endothelium failure, but is not able to correct corneal scarring, thinning or surface irregularity.
Not all patients with corneal pathology are candidates for DSEK. The indication depends on decreased vision related to corneal swelling from poorly functioning endothelium. The main indications are:
- Acquired Pseudophakic or Aphakic bullous keratopathy, Failed previous graft.
- Inherited Fuchs' Endothelial Dystrophy
The ideal time to perform DSEK to prevent permanent change is unclear. However, accordingly to a recent study  early DSEK influences visual outcomes in Pseudophakic Corneal Edema. There is a significant relationship between Cataract Extraction to DSEK time and Best Spectacle Corrected Visual Acuity. Performing earlier (<6 M) DSEK for pseudophakic corneal edema appears to be associated with improved visual outcomes. 
This procedure, which takes approximately 45 min, is done under local or general anesthesia. First the endothelium and Descemet’s membrane of the cornea is stripped away through a corneal incision. Then a circular disc is removed from the inner lining of a donor cornea. This thin layer is then transplanted into the recipient eye and attached to the posterior cornea of the recipient. 
Donor tissue preparation: Corneoscleral buttons are excised from donor globes and stored by organ culture. Each globe is mounted on a purpose-designed holder and the anterior chamber is filled with air to create an air-endothelium interface. With dissection spatulas, a manual stromal dissection is made at approximately 95% stromal depth using air-to-endothelium reflex to monitor dissection depth. Stromal dissection is extended up to limbus over 360 degrees. After dissection is completed, a 16.0 mm corneoscleral rim is excised from each globe and the endothelium is evaluated with an inverted light microscope and stored in organ culture until time of transplantation.  Various donor graft thicknesses are available and fall into the four general categories: nanothin Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) (15–49 µm), ultrathin DSAEK (50–99 µm), thin DSAEK (100–149 µm) and conventional DSAEK (150–250 µm).
Surgical technique: With a reverse Sinskey hook, a circular portion of Descemet membrane is scored and stripped from the posterior stroma so a descemetorhexis is created and the central portion of Descemet membrane is removed from the eye. A temporal self-sealing 5.0 mm sclerocorneal incision is created with a crescent knife. After trephinating an 7.5 to 9.0 mm diameter DSEK-graft from the predissected corneoscleral rim, the tissue is often stained with Trypan Blue. The graft can be inserted with a wide variety of techniques. Irrigating inserters, push-through and pull through techniques exist. Irrigating inserters rely on the adhesion between the insertion platform and the posterior stromal surface as the insertion platform gently springs open in the anterior chamber. Push-through techniques rely on forceps, hooks bent-needles and glides to slide a graft into the anterior chamber, usually on a film of viscoelastic. Pull-through techniques is a two-handed maneuver employing specialized forceps or suture position on the opposite side of the main wound to draw the donor disc into the anterior chamber, with or without a glide. Finally, a manual folding forceps insertion technique requires the surgeon to fold the graft in a 60%/40% ratio, like a taco, and carefully insert and rotate the graft to the appropriate position.  . If a glide is used for insertion, it is removed from the main wound, and the DSEK graft is unfolded in the recipient anterior chamber, taking care to avoid excessive touch between the donor endothelium and the underlying iris and lens. Balanced salt solution, an air bubble, or instrument manipulation may be used to assist in the unfolding of the graft. After unfolding, the graft is positioned against the posterior stroma of the host using a small air bubble. The DSEK graft is then carefully positioned centrally using a variety of brushing, tapping , sweeping and dragging techniques. After the DSEK graft is positioned centrally, the anterior chamber is completely filled with air. . Dilating drops may be used to prevent any pupillary block from air bubble. Peripheral iridotomies can also be performed to reduce the chance of pupillary block. Once the donor disc is in tight apposition with no or minimal interface fluid between the donor and the recipient stroma, the surgeon partially removes the air in the anterior chamber and replaces it with BSS. An air bubble of approximately 8 to 9 mm is usually left in place to help further stabilize the donor disc position over the first 24 hours postoperatively.  The air bubble pushes the graft in place until it heals in an appropriate position, giving time for the pumping action of endothelium to help the donor tissue bind to its new host . The structure of the cornea remains intact.
After the surgery, the patient lies in a supine position, flat, facing the ceiling, for the first hour after surgery and then as much as possible to allow the retained air bubble to further stabilize the graft position, but this is not critical. The patient is discharged following this outpatient procedure when fully recovered from the anesthesia. 
Postoperative care should include broad-spectrum antibiotics to prevent infection and steroids (initially dexamethasone, then fluorometholone) to prevent rejection.  Patient should lie in the supine position for one more day after DSEK (to utilize the residual air bubble in the anterior chamber) and to not rub their eye for 2 weeks after DSEK surgery. 
Advantages and Challenges
DSEK Procedure Advantages
- Less Invasive, smaller surgical incisions
- No corneal-graft sutures
- Faster visual recovery
- Less risk of sight threating complications and less induced astigmatism
- Post-surgery stronger eye (less prone to injury)
- Less risk of immune rejection of the transplanted corneal tissue
- Shorter post-operative care
- Increase overall donor tissue availability , using the posterior layer of the donor cornea in one patient and the anterior lamellar graft in another patient.
- Faster to learn. DMEK Surgical technique may require more training, technically more challenging. 
DSEK Procedure Challenges
Compared with DMEK:
- Final Best Corrected Visual Acuity (BCVA) may be suboptimal .  Optical irregularities due to stromal layers being transplanted in DSEK. For nano-thin DSEK, final BCVA was comparable to DMEK, demonstrating the significance of thinner donor graft preparation. 
- Slower visual rehabilitation compared to DMEK.  However, visual recovery is expedited with use of thinner corneal grafts. 
- Interface problems, folds in the donor disk from maladaptation to the recipient stroma, hyperopic shift, decentration of the donor disk, and excess donor corneal thickness. 
- DSEK grafts are less likely to require rebubbling procedures. 
- Limited accessibility (investments in equipment)
- Drop in Donor endothelial cell density in the early post-operative phase. 
- Graft Dislocation: graft moves from its intended position. Dislocation rate is significantly higher in DSAEK groups than DSEK.  Donor tissue reposition is easily treated by taking the patient back to surgery, and usually under topical anesthesia, with a 15 minute operation, another air bubble is placed in the anterior chamber and the disc is repositioned. 
- Primary graft failure: Some studies suggest a primary graft failure rate of 5.7% . Endothelial pump function has an important role in graft adhesion. In many cases, graft fails to adhere because the surgeon was too aggressive in handling it, and damaged endothelial cells.  DSAEK showed significantly poorer graft survival than DSEK (P = 0.013), apparent only 18 months after graft. 
- Graft Rejection: Rejection can develop months or years after the transplant. Against PK, initial rejection symptoms after DSEK procedure are usually subtle. Patients can be asymptomatic. When patients show redness, blurry vision and light sensitivity the rejection is severe. To prevent rejection patients should be under a closed follow-up care and kept on a prophylactic tapering down eye drop steroids regimen.
- Cell loss: Assessing endothelial cell density (ECD) after DSEK, it is expected a median cell loss of 32% in the perioperative period. After that the ECD declines at a linear rate of approximately 110 cells/mm2 per year between 6 months and 10 years after DSEK . Gradual reduction in endothelial cell density over time can lead to loss of clarity and require repeating the procedure.
Follow up care
- Slit lamp biomicroscopy: to ensure that the graft is fully attached and to look for signs of rejection (scattered keratic precipitates, edema or conjunctival hyperemia). Fig. 1.
- Check IOP: monitor for steroid-induced pressure spikes.
- Check refraction after first month.
- Check central corneal thickness: a graft that is getting thicker over time may be failing and a graft that gets thicker suddenly signals rejection.
- Graft detachment: Anterior segment OCT can assess for graft detachments. Fig. 2. If the graft is detached, it will need to be reattached by rebubbling the anterior chamber. Since the graft has been in aqueous fluid, it often works well after reattachment. 
Even though DSEK/DSAEK may be the current standard, the newer partial thickness Descemet’s Membrane Endothelial Keratoplasty may have better clinical outcomes and may also require less investment in preparation of isolated Descemet grafts. A study  compared outcomes after DMEK and DSEK during the surgeon’s DMEK learning curve and there was some evidence of improved visual acuity outcomes in DMEK. They observed worse 6-month endothelial cell loss among DMEK patients.  A Cochrane Review found that it was difficult to draw any conclusion regarding endothelial cell loss as two trials demonstrated no difference and two studies reported that DMEK had higher cell counts at one year. 
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