What is the Cornea?

The cornea is the clear tissue that covers the surface of the eye.  It is the window of the eye, focusing light as it passes and allowing for crystal clear vision.  When light enters the eye, it passes through while being slightly focused by the cornea.  It then goes through the pupil (the dark spot in the middle of the iris). Behind the pupil is the natural lens of the eye, which further focuses the light onto the retina (the light sensitive film) at the back of the eye. The retina sends this signal from the eye to the brain.  The eye functions can be compared to a camera, with a system of lenses (cornea and lens), aperture (pupil) and film (retina).

The cornea must remain clear to have perfect vision. A number of problems may damage the cornea, causing light to be defocused and reducing the vision. Corneal scarring from trauma or infection, keratoconus, or other inherited corneal conditions can cause these problems.  If the cornea is the cause of reduced vision, spectacles or contact lenses may not be able to improve the vision.  A cornea transplant may be necessary to replace the cloudy cornea to improve the vision.

Types of Cornea Transplants

The cornea consists of five layers, each with its own types of cells that carry out its distinct functions.   As seen in the image below, the layer include the epithelium, Bowman’s membrane, stroma, Descemet’s membrane, and endothelium.  Cornea transplants can be used to replace all or some of these layers.

Types of cornea transplants include:

Penetrating (full thickness) cornea transplant. This involves transplanting all the layers of the cornea from the donor.  Click here for more information on full thickness cornea transplants.

Lamellar (partial thickness) cornea transplant. During this procedure, only some of the layers of the cornea are replaced with the transplant.  Click here for more information on lamellar cornea surgery.

In a lamellar cornea transplant, selected layers are transplanted, which can include the deepest layer, called the endothelium (posterior lamellar cornea transplant). Commonly performed versions of this procedure include Descemet’s Stripping Endothelial Keratoplasty (DSEK) or Descemet’s Membrane Endothelial Keratoplasty (DMEK).  A lamellar transplant can include layers closer to the surface (anterior lamellar cornea transplant).  A commonly performed version of this procedure  is the Deep Anterior Lamellar Keratoplasty (DALK).  Lamellar transplants may be more appropriate than full thickness penetrating transplants when the disease process is limited to only a few layers of the cornea.