Descemet’s membrane endothelial keratoplasty (DMEK) is a partial thickness procedure where the surgeon replaces the host Descemet’s membrane (DM) and endothelium with donor DM and endothelium. DMEK differs from Descemet’s stripping endothelial keratoplasty (DSEK) which involves the replacement of the posterior stroma alongside the DM and endothelium. DMEK belongs to the category of endothelial keratoplasty (EK).
DMEK is not suitable for patients with stromal scarring and healthy endothelium like in keratoconus. Such patients require penetrating keratoplasty (PK). It is also not suitable for the following conditions:
- Previous glaucoma surgery
- Aniridia or large iris defects
- Anterior chamber intraocular lens
Candidates suitable for DMEK include:
- Bullous keratopathy
- Fuchs corneal dystrophy
- Iridocorneal endothelial (ICE) syndrome
- Posterior polymorphous corneal dystrophy
- Congenital hereditary endothelial dystrophy
- Other causes of corneal endothelial dysfunction
Before the Procedure
Before the procedure, the tissue is prepared following the laid down regulations. The donor should be aged two to 75 years with donor tissue preserved for a maximum of seven days. The surgeon may prepare the tissue just before the procedure or have an eye bank prepare it.
The patient will have their medical history taken and eye tests conducted. In the eye tests, the doctor takes measurements, including corneal thickness, pupil dilation, and refractive error. A significant test that will be done is the optical coherence tomography (OCT). Patient education and counselling are equally important because the patient needs to understand the risks and benefits and have realistic expectations.
The patient will be put under local or general anesthesia. In the procedure, the surgeon:
- Creates paracentesis sites (2-4) and uses Healon to fill the anterior chamber
- Using a Sinskey hook and needle, creates an inferior peripheral iridotomy. This action prevents pupillary block postoperatively
- Uses a circular ring to mark the recipient's corneal epithelium to create a host tissue resection template
- Peels off the DM from the overlying stroma
- Using a keratome, temporarily creates an incision and uses forceps to remove the now free DM
- Removes the Healon and normalizes pressure by constricting the pupil with an injection
- Carefully submerges the donor tissue in trypan blue solution for one minute. This action stains the tissue for visibility purposes
- Places the tissue in a balanced salt solution and aspirates it into a modified glass Jones tube. The glass tube’s tip is inserted into the incision, and donor tissue injected into the anterior chamber
- Flattens the anterior chamber
- Taps and swipes on the anterior corneal surface to unscroll the graft. S/he secures the graft through an injection into the anterior chamber and waits about 15 minutes for adhesion
- Uses a nylon suture to close the main incision
- Assesses graft adhesion and checks for any gas trapped behind the iris by performing an air-fluid exchange.
- Uses another injection to cover the graft
Risks & Complications
The risks and complications may include:
- Pupillary block
- Subepithelial haze
- Anterior synechiae
- Upside down grafts
- Descemet graft folds
- Cystoid macular edema
- Epithelial defect/erosion
- Interface pigment deposits
- Iatrogenic primary graft failure
- Tissue damage in the preparatory stages
- Elevated intraocular pressure or glaucoma
- Graft detachment depending on surgeon experience
Aftercare & Recovery
After surgery, the patient lies on their back (supine) as much as possible for the first two days or longer. The surgeon will prescribe topical antibiotics for one week. The patient will use prednisolone acetate 1% every two hours while awake. Prednisolone acetate is used for the first week, four times a day for three months. It is then slowly tapered and stopped after one year. This medication helps to prevent graft rejection and prevent the increase in IOP.
Patients will be seen the following day, and later followed up at one week. The next visit occurs in the second week, then in the first month, third month, sixth month, and one year. The patient may undergo an OCT before the procedure followed by the first day after surgery, then after a week, and after one month to assess the stroma and the graft’s edge position. If the stroma is significantly edematous, it may be an indication that the graft is either upside down or is not functioning well.
Research indicates that DMEK is the technique that offers the most rapid visual rehabilitation of all keratopathy techniques. DMEK presents with minimal optical interface effects; therefore, registers outstanding final visual acuity. The procedure also has a lower allograft rejection risk due to the transplantation of less tissue. Compared to other keratoplasty procedures, DMEK has less long-term reliance on topical steroids. These steroids can be discontinued before one year is over, especially in patients with glaucoma.
Studies have reported that patients can have visual acuity of 20/20. Refraction after surgery can be stable at three months without significant spherical equivalent change between three and six months after surgery.