Corneal Transplants
What is the Cornea?

The cornea is the clear front part of the eye that allows light to pass into the eye.   It is the part of the eye where a contact lens is placed.  Externally, the cornea is a circular transparent tissue that has a diameter of about 12mm.  The thickness of the cornea is about 0.5mm.  When looking at the cornea from the side, it has a curvature that bends forward.    Its primary function is to provide a clear and focused image by acting as a lens in the optical system of our eye.  The cornea also helps protect against infection.

For practical purposes, the cornea consists of three main layers:  epithelium, stroma, and endothelium.  The epithelium is the surface of the cornea that is exposed to the air and tears.  It has a thickness of only 7 cells, which is about 50 microns.  The epithelium continually regenerates throughout our life just like the surface of our skin.  A healthy epithelium provides a strong barrier against infection by preventing unwanted organisms from entering into the deeper layers of the cornea.  The epithelium requires constant lubrication with tears, and must have functioning stem cells to generate new epithelial cells throughout our lives.  A problem in the corneal epithelium can cause poor vision, discomfort, and infection.

The middle and thickest layer of the cornea is called the stroma.  It is made up of cells and protein fibers that are neatly arranged to provide corneal clarity, just like a window pane.  If the stroma gets infected or injured, a relatively opaque scar will be left in that area.  This loss of clarity may affect vision if it lies in front of the pupil near the visual axis.

The innermost layer of the cornea is called the endothelium.  It is one cell layer thick.  These cells continually pump water out of the cornea to keep it thin and clear.  If these cells are damaged or if they become dysfunctional, then the cornea will soak up water and become thick and hazy.  This swollen, edematous cornea ultimately degrades the vision and may cause discomfort.  Unfortunately, the endothelial cells cannot self-regenerate to restore corneal clarity.

Injuries to the cornea

A common acute eye problem is an abrasion or scratch to the cornea.  Often a fingernail, paper cut, tree branch, or a foreign body can cause a corneal abrasion.  Symptoms of an abrasion include moderate to severe eye pain, foreign body sensation, tearing, light sensitivity and redness.  Sometimes the foreign body is still present after the injury and must be removed.  The cornea also can become infected after an abrasion.  Therefore, it is recommended to visit an eye care professional for proper diagnosis, monitoring, and treatment.

Infections to the cornea

Fortunately, infections of the cornea are not common, but they can be very serious causing permanent vision loss.  An infection in the cornea can be caused by a bacteria, virus, fungus, or protozoan.  Those primarily at risk are contact lens wearers, especially if the lenses are not properly worn or cared for.  Other risks for cornea infection include recent eye trauma, eye surgery, and pre-existing eye diseases.  Cornea infections cause moderate to severe eye pain, redness, light sensitivity, and decreased vision.  Prompt medical care should be sought if any of these symptoms develop.  Treatment includes frequent instillation of antibiotic eye drops, sometimes requiring hospital admission.  Cornea transplantation may be required.

Cornea Transplantation

Transplantation of the cornea is a surgical procedure that involves removing part or all of the diseased cornea, and replacing it with part or all of a healthy donor cornea.  The surgery is performed to improve vision, reduce pain, or maintain the integrity of the eye.  Donor cornea tissue is harvested from the eyes of organ donor individuals who have died.  The tissue is then brought to a local eye bank where it is examined to make sure it is suitable for transplantation and to screen for infectious diseases.  Donor corneas can then be stored in preservative solution for days until ready for surgery.  Unlike other organ transplantation, corneas do not need to be genetically matched.  This is because the cornea has no blood vessels to allow immune system cells to recognize the tissue as foreign.  These facts offer convenience to the patient and surgeon for scheduling surgery.

Penetrating keratoplasty is a type of cornea transplantation in which the entire central cornea is excised and replaced with a full thickness healthy donor cornea cut to fit the area.  Several small non-absorbable stitches are placed to hold the new cornea into place.  The stitches are removed in the office, but most of them stay in for at least one year.  Penetrating keratoplasty may be performed electively on patients with scars, keratoconus, Fuchs’ dystrophy, bullous keratopathy (cornea swelling) and other inherited cornea problems.  Rarely, this surgery is done emergently for trauma or severe cornea infections.

Lamellar keratoplasty is another type of cornea transplantation that involves removing only the diseased layer of the cornea.  The diseased area is replaced with the same layer of healthy donor tissue.  Anterior lamellar keratoplasty is a technically challenging surgery in which the top layers are removed leaving the patient’s cornea endothelium intact.  This procedure can be done for cornea scars or keratoconus.  Posterior lamellar keratoplasty is done for Fuchs’ dystrophy and bullous keratopathy.  It involves removing the dysfunctional endothelial layer and transplanting a new layer of endothelium.  Today it is known as Descemet’s stripping automated endothelial keratoplasty (DSAEK).

Refractive surgery

The majority of refractive surgery involves changing the shape of the cornea.  Laser in situ keratomileusis (LASIK) and photorefractive keratometry (PRK) are the two most common laser refractive procedures to correct nearsightedness (myopia), farsightedness (hyperopia), and astigmatism.  An excimer laser is used in LASIK and PRK to modify the shape of the cornea to correct these refractive errors.  An older form of refractive surgery, called radial keratotomy (RK), involved making small precise incisions in the cornea with a diamond blade to alter the corneal shape.

Where Can I Get More Information?

Your eye doctor is the best source of information on cornea eye diseases.

To schedule an appointment call 414-271-2020