The cornea is a thin, clear, spherical layer of tissue on the surface of the eye that provides a window for light to pass through. In a healthy eye, the cornea bends or refracts light rays so they focus precisely on the retina in the back of the eye.
There are many diseases that can affect the cornea, causing pain or loss of vision. Disease, infection or injury can cause the cornea to swell (called "edema") or degrade (become cloudy and reduce vision). Common diseases and disorders that affect the cornea include:
- Bullous Keratopathy
- Conjunctivitis ("Pink Eye")
- Dry Eye
- Fuchs' Dystrophy
- Inherited Corneal Dystrophies (Granular, Lattice)
- Glaucoma (High Eye Pressure)
- Keratitis (Viral Inflammation)
- Ocular Herpes
- Shingles (Herpes Zoster)
- Stevens-Johnson Syndrome
Treatment for corneal disease can take many forms, depending on the underlying problem, as well as the patient's preferences. Some conditions resolve on their own and many can be treated with medication. If the cornea is severely damaged or if there is a risk of blindness, a corneal transplant may be recommended to preserve vision.
The cornea is the clear covering of the front of the eye which bends, or refracts, light rays as they enter the eye. For clear vision to occur, the cornea must have the correct shape and clarity to focus incoming light rays precisely on the retina at the back of the eye. When the cornea becomes cloudy or misshapen from injury, infection or disease, transplantation may be recommended to replace it.
Penetrating Keratoplasty- PKP; Deep Anterior Lamellar Keratoplasty - DALK
There are several different corneal transplant procedures available to help restore vision in patients with corneal problems.
If your eye disease process involves all layers of the cornea, you may need a penetrating keratoplasty (PKP), or full thickness cornea transplant. PKP surgery consists of removing the entire cloudy cornea and replacing it with a full thickness human donor cornea from an eye bank, thereby replacing all layers of the cornea. The eye surgeon removes the damaged cornea by making a circular cut or incision and replaces the damaged cornea with the donor cornea, which is kept in place with stitches (sutures). These sutures are thinner than human hair. This type of surgery can be combined, if needed, with other eye surgeries, such as cataract removal surgery. The operation typically takes 45 to 60 minutes.
The advantage of the traditional corneal transplant operation is its long and successful history of treating corneal blindness. The visual recovery after a PKP may take up to 6 to 12 months. Often, new contact lenses and/ or glasses are needed in order for the eye to reach its full visual potential.
If your corneal problem is primarily located in the outer layers of the cornea, your surgeon may offer you a deep anterior lamellar keratoplasty (DALK), a partial corneal transplant, which will leave behind your innermost corneal layers (Descemet's membrane and endothelium) while replacing all of the outer layers of the cornea (stroma and epithelium). The advantage of a DALK (if your eye is eligible and if the structures of your cornea withstand the stress of the procedure) is that you will be able to keep your own healthy endothelium (innermost layer of the cornea), thus eliminating endothelial corneal tissue rejection (one type of corneal rejection that may occur after a PKP, which is the full-thickness corneal transplant). If your surgeon is offering you a DALK corneal transplant, that surgery involves more steps and therefore usually takes at least 1-2 hours to accomplish.
Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) and Descemet Membrane Endothelial Keratoplsaty (DMEK)
In some corneal conditions, only the innermost layer of the cornea is damaged, while the other layers remain healthy. Technological and surgical advances have allowed for the development of specialized procedures that replace only the diseased part of the cornea, while leaving the healthy parts intact.
Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK) are both techniques used to replace only the damaged innermost layer of corneal cells, known as the endothelium, with healthy human donor corneal cells. The DSAEK graft consists of donor corneal endothelium along with a minimal amount of posterior stroma (additional donor corneal tissue), where as the DMEK graft is even thinner and consists of only a single cell layer of donor corneal endothelial cells. DMEK is a highly advanced, newer surgical approach which leads to the exact anatomic restoration of a patient's cornea after a partial transplant surgery.
Both procedures are performed through a much smaller incision with much shorter recovery times and fewer risks than a traditional corneal transplant (PKP).
DSAEK and DMEK surgeries are most commonly performed on patients with Fuchs' dystrophy and pseudophakic bullous keratopathy. Both diseases cause the cells of the corneal endothelium to deteriorate, resulting in corneal swelling and distorted or hazy vision. As these conditions progress, vision continues to worsen as damaged cells cannot regenerate or grow back.
DSAEK and DMEK Procedure
During the DSAEK or DMEK procedure, your surgeon will make a small incision in the cornea, the front clear part of the eye. This incision allows the surgeon to access the cornea and remove the damaged endothelial cells using special surgical instruments. The donor tissue is then inserted into the eye and the incision is closed with one or more sutures.
After the donor tissue has been inserted and positioned in the eye, an air bubble (DSAEK procedure) or gas bubble (DMEK procedure) is injected into the eye in order to properly support the donor corneal graft and lead to graft adherence. These procedures are performed with both a topical anesthetic and/ or an injectable anesthetic to minimize any potential discomfort. The procedures only takes about 40 to 60 minutes to perform, although patients should plan on being at the surgical facility for about two hours.
Recovery from DSAEK and DMEK
After the DSAEK and DMEK procedures, patients will be moved to a recovery room, where they will be monitored for about 30-60 minutes before being able to go home. Your surgeon will prescribe antibiotic and steroid eye drops to be used as the eye heals. You will need to return to your doctor the next day for a follow-up appointment. After the DSAEK surgery, you must remain lying on your back (face up towards the ceiling) at home for one day (usually the same afternoon as the day your surgery took place). After the DMEK surgery, this positioning must be maintained for a few additional days in order to ensure proper graft attachment of the very thin and fine corneal tissue.
After DSAEK surgery, most patients notice improvements to their vision within the first two weeks after surgery, with results continuing to develop over the next six to eight weeks. The visual recovery takes only about 1 week to 1 month following the DMEK surgery.
There are several significant advantages to the DMEK operation compared to the DSAEK procedure. The DMEK operation replaces just the inner single cell layer of the cornea, as compared to this single cell layer along with multiple layers of additional corneal tissue in a DSAEK. With a DMEK, over 97% of the patient’s own cornea remains intact and contributes to the structural integrity of the eye. The final best corrected vision after DMEK (with newest glasses and/ or contact lenses) has been shown to be superior (in multiple studies) as compared to DSAEK, there is also faster visual recovery and a lower rate of graft rejection following DMEK. The superiority of the DMEK procedure is thought to be related to the thinner graft size used in a DMEK as compared to a DSAEK.
Not all patients are candidates for a DMEK, and therefore the better and safer surgical option remains a DSAEK. Your ophthalmologist will be able to assess which surgery is most appropriate for your eye condition.
Risks of DSAEK and DMEK
While the DSAEK and DMEK procedures are considered safe for most patients with cornea damage, there are certain risks involved with any type of surgical procedure, including infection, bleeding and more. Although rare, there is a risk of transplant rejection, which may result in redness, sensitivity to light and blurred vision. On occasion, the transplant may fail to function and a repeat surgery may be needed to replace the corneal graft with a new corneal donor tissue.
To learn more about the DSAEK and DMEK corneal transplant procedures, and to find out whether or not this procedure is right for you, please call us today to schedule a consultation with Dr. Lauren Schneider MD, our experienced cornea transplant specialist.