CORNEA
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:
Allergies
Bullous Keratopathy
Conjunctivitis ("Pink Eye")
Dry Eye
Fuchs' Dystrophy
Inherited Corneal Dystrophies (Granular, Lattice)
Glaucoma (High Eye Pressure)
Infections
Keratitis (Viral Inflammation)
Keratoconus
Ocular Herpes
Pterygium
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.
Corneal Transplants
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).
