Descemet’s membrane endothelial keratoplasty (DMEK) is a partial thickness corneal transplant that replaces the corneal endothelium (innermost portion of the cornea) rather than the full thickness of the cornea as in standard corneal transplants.
DSAEK and DMEK are indicated when there is corneal clouding due to a dysfunction of the endothelium but where the other layers of the cornea remain healthy. With Fuchs’ endothelial dystrophy or when there is swelling of the cornea after cataract surgery, it is the endothelium which is compromised.
What is the endothelium and how does it work?
The cornea is the clear dome that makes up the front part of the eye. It is about 1/10th of a centimeter thick and is composed of three primary layers: the epithelium, the stroma, and the endothelium. The epithelium is a thin surface layer. The stroma is composed mostly of fibrous proteins and acts like a sponge, absorbing fluid from inside the eye. The endothelium is a single layer of cells coating the inside portion of the cornea. Its job is to provide nutrients to the cells in the stroma and to make sure that the stroma has just the right amount of fluids. Too much fluid in the stroma can cause swelling of the cornea and decreased vision.
What is endothelial failure?
The cells of the corneal endothelium are very fragile. Two of the most common causes of endothelial failure are Fuchs’ Dystrophy, an inherited disease and trauma following cataract or glaucoma surgery. Once an endothelial cell dies it will not grow back. If an eye loses too many endothelial cells, it is not able to maintain the proper corneal thickness and clarity.
Advantages of DMEK compared to standard corneal transplantation
- The eye surface is kept intact, thus remaining more resistant to injury and infection
- There is minimal change in refraction because only the endothelial layer (~5% of the cornea) is replaced
- Suture-related problems are significantly reduced/can be eliminated
- Visual recovery is significantly faster and better
Preparing for DMEK Surgery
Do not eat or drink anything for at least 8 hours prior to the surgery. Needed medications can be taken with a small sip of water. It is important to continue taking the medical eye drops (e.g. for glaucoma) that you would normally use on the same day as the surgery.
The procedure is done through a small incision on the side of the cornea and usually takes about 30 minutes to complete. DMEK involves peeling the diseased endothelial layer from the back of the cornea and leaving the healthy remainder intact (approximately 95%). The donor Descemet’s Membrane with healthy corneal endothelium is placed inside the eye through a small incision and positioned with an air bubble in the place of the diseased layer.
Donor Disc Dislocation
What is the cornea?
The cornea is the clear covering of the front of the eye that focuses incoming light. To maintain clear vision the cornea must have the correct shape and clarity. When the cornea becomes cloudy or misshapen, a corneal transplant may be indicated to restore vision, alleviate pain or repair eye integrity.
With corneal transplants, scarred or damaged tissue is replaced with healthy donor tissue. Corneal transplants either replace the whole cornea (standard full thickness known as Penetrating Keratoplasty) or individual layers (partial thickness known as DSAEK, DMEK and DALK). The type of transplant performed depends on the prior condition and extent of the damage.
Indications for full thickness corneal transplants
- Advanced keratoconus with severe scarring
- Severe Herpetic scarring
- Full thickness traumatic injury
Indications for DSAEK and DMEK
- Fuchs’ dystrophy
- Corneal failure after cataract, glaucoma or retinal surgery
- Endothelial failure or rejection of a full thickness transplant
Indications for DALK
- Keratoconus, corneal scarring & pellucid marginal degeneration
- Stromal Corneal Dystrophies
- A healthy endothelium (the innermost layer of the cornea)
How do I know if I would benefit from a corneal transplant?
A corneal transplant is normally indicated once your damaged cornea interferes with your ability to do activities important to you or is causing significant constant pain not treatable by other means.
The role of the Eye Bank of B.C.
Every year in B.C. over 500 people require a corneal transplant which uses tissue generously gifted by registered organ donors who have passed away. All donated corneas are verified to be healthy, clear and appropriate for you.
How is the surgery performed?
Corneal transplants are generally done under local anaesthetic. With full thickness transplants, the damaged cornea is removed through a process called trephination and replaced with a donor cornea. The transplant is then secured using tiny stitches about 1/3 the thickness of a human hair. Partial thickness transplants replace only certain layers, leave the rest intact and use fewer stitches. On treatment day, you will be instructed to arrive at the hospital about 1.5 hours in advance and the surgery will take approximately 30 minutes. No overnight hospital stay is required.
The success rate of corneal transplants has drastically improved in the last 30 years. Today, the overall success rate is above 85%. However, it can vary from 50% to 95% depending on the condition being treated. Dr. McCarthy will go over your individual case with you.
Corneal transplants remain a serious surgery with certain risks that you should be aware of. The primary risks are rejection and infection which are minimized with the use of antibiotic and steroid drops. Other less common complications include bleeding, swelling, glaucoma and retinal detachment. Fortunately, the majority of complications are treatable and have good outcomes. Dr. McCarthy will inform you if you are at an increased risk for any of the above complications.
How long is healing time?
Healing time is different for everyone. You can expect to have moderate discomfort, irritation and redness for up to 3 weeks. Best possible vision is achieved once wounds have fully healed and stitches removed. Healing of a full thickness transplant can take up to 1 year. Visual improvement with DMEK and DSAEK usually occurs in a few weeks.
What do I need to do before and after surgery?
You should ensure that you understand all instructions provided. You will start taking antibiotic drops 3 days prior to surgery and continue until the bottle is empty. You will also take steroid drops that will be gradually reduced over time to 1 drop per day, but you will likely continue permanently. It is essential to take your drops as prescribed to maintain function of the transplant. After surgery you should avoid any heavy lifting and strenuous activity for 1 month.