What is the Cornea?

The cornea is the eye’s outermost layer. It is the transparent, dome-shaped surface that covers the front of the eye as depicted in the diagram. The main function of the cornea is to allow light to pass into the eye, so that it can reach the lens and the retina. A second chief function of the cornea is to help focus light, much like a camera lens.

Healthy Cornea

Corneal health depends on a number of factors, including the health of the conjunctiva and of the eyelids. The conjunctiva is the tissue which covers the front part of the eye (but not the cornea) and lines the back of the eyelids. Both the conjunctiva and the eyelid contain glands that create the tear film, which is essential to the maintenance and overall health of the cornea.

Diseased Cornea

Diseases and conditions affecting the cornea can cause distorted vision or vision loss. Keeping the cornea healthy is a vital aspect of protecting your sight and the health of your eyes. Learn more below about the expert treatment available ask the experts at St. Michael’s Eye & Laser Institute for a variety of corneal conditions and diseases.


A pterygium is a non-cancerous growth of the thin mucous membrane, or conjunctiva, which lines the ocular surface beyond the cornea. Many patients who develop this corneal condition work in outdoor environments in which they are exposed to sand, dust, wind, and sunlight. When a pterygium does not respond to eye drops, or if it causes vision problems, pterygium excision surgery can be a helpful treatment method. During this procedure, the pterygium is removed and the bare area is replaced with a skin graft taken from the ocular surface.


If corneal conditions have not responded to medication or other treatments, the next step might be a corneal transplant surgery. The expert corneal surgeons at St. Michael’s Eye & Laser Institute perform several different types of corneal transplants, which are dependent on the patient’s specific needs. Listed below are the three most common types of corneal transplants performed by the eye surgeons at St. Michael’s Eye & Laser Institute:

  • Penetrating Keratoplasty, or PKP, is a full-thickness transplant of the cornea.
  • A DALK Corneal Transplant, or deep anterior lamellar keratoplasty, is a surgical technique in which most of the cornea is replaced while preserving the thin posterior membrane of the eye.
  • A DSAEK Corneal Transplant, or Descemet’s Stripping Automated Endothelial Keratoplasty, replaces only the damaged posterior layer, while preserving the rest of the cornea.