I often describe the cornea to my patients as the clear, front window of the eye that covers the colored iris. When a patient presents with an abnormality in the cornea, I explain to them that the cornea has several layers, and in the most basic sense, can be thought of as having an outer, transparent skin cell layer, a middle collagen layer, and an inner cell layer. Patients typically have one or more layers affected by a given disease/trauma/infection etc., at a single time. Sometimes, the layers are so altered, that the cornea becomes opaque, and the only way to restore vision is with a cornea transplant.
I liken the cornea to the windshield of a car, and the retina (the inner wallpaper that covers the inside, posterior chamber of the eye) to the car’s engine. I tell my patients that, as long as their engine is working properly, transmitting visual signals to the brain, I can replace their windshield a number of different ways to restore the sight.
The great thing about cornea transplant today, is that we have the ability to replace only the layer/layers that are affected by disease, leaving the patient’s healthy cornea tissue intact. This much decreases the chances of rejection or failure of the transplanted human donor cornea tissue.
A human cornea, on average, is about 540 micrometers thick. Some people have thicker, and some people are born with thinner corneas. When a cornea transplant surgeon performs what is known as a DMEK ( Descemet’s Membrane Endothelial Keratoplasty), the surgeon is exchanging only the inner 10 micrometers of the patient’s cornea with 10 micrometers of the donor’s cornea. This procedure is performed for inherited genetic abnormalities in the inner layer of the cornea, with Fuchs’ dystrophy being the most common. Damage to the inner cell layer of the cornea, by other surgery in the eye or infection for example, can lead to the need for replacement as well.
DSEK (Descemet’s Stripping Endothelial Keratoplasty) is the predecessor form of transplant to DMEK, and is performed for the same reasons DMEK is performed today. In DSEK, the surgeon replaces the innermost 10 micrometer layer of the patient’s cornea, as well as transplants about 40-70 micrometers of the middle layer of the donor tissue onto the host (patient) cornea. We knew how to perform DSEK before we knew how to effect DMEK. DMEK is a more technically challenging procedure to DSEK, as the tissue is much thinner, and there are still anatomical reasons sometimes as to why DSEK may be a preferred procedure. However, visual acuities are much better with the DMEK procedure, and many cornea surgeons have made the transition to DMEK for inner cell layer disease.
PK ( Penetrating Keratoplasty) is a replacement of the entire patient’s cornea with donor cornea. The entire cornea needs to be replaced in disease that effects all layers of the cornea. There are few reasons today to replace the entire cornea. More typically, surgeons are performing DALK (Deep Anterior Lamellar Keratoplasty). DALK is a replacement of all layers of the cornea, except for the inner cell layer. Contact lens related cornea ulcers that lead to scarring of the anterior most layers, and some inherited cornea dystrophies, lead to a need for DALK.
When a patient has failed three or more penetrating keratoplasties, or is a poor candidate for human cornea transplantation for whole-body health issues that may lead to quick failure of the transplanted tissue, the patient may be a candidate for an artificial cornea transplant. An artificial cornea transplant can give a patient very good vision, but requires a different management schedule that a human cornea transplant.
- AAO - Cornea Anatomy
- AAO - Corneal Ulcer
- AAO - Corneal Dystrophies
- AAO - Corneal Abrasion
- AAO - Corneal Erosion
- AAO - Corneal Laceration
- AAO - What Is Keratoconus?
- AAO - What Is Dry Eye?