The Cornea

The cornea is the clear "window" covering the front of the eye which allows the light to pass through to the retina which enables us to see. It is the main focusing element of the eye.To stay clear the cornea must be healthy. If the cornea is damaged it may become swollen or scarred. This may be due to injury, disease, infection or hereditary corneal failure. In these cases either the cornea's smoothness or clarity may be lost. The scars, swelling or irregular shape cause the cornea to scatter or distort light resulting in loss of vision. The first corneal transplant was performed in 1905.

The need for corneas

The first corneal transplant in Victoria was done in the 1940's. Except for blood transfusion it is the oldest and most frequently performed transplant procedure. In Australia, approximately 1300 corneal transplants are required each year.

Why are corneas transplanted?

The two most common reasons for requiring a transplant are a clouding over and loss of transparency in the cornea in later life, as is the case with Bullous Keratopathy, or to the loss of the smooth rounded shape of the cornea meaning that light can not be regularly focussed into the eye, as occurs in Keratoconus. Other problems which may require a transplant include herpes virus infection of the eye, accidental injury to the eye, corneal scarring due to other trauma, hereditary or congenital corneal clouding, or severe bacterial infection.

Keratoconus

This condition involves the central cornea thinning and bulging forward, and may also be associated with central corneal scarring. It is usually bilateral though frequently one eye is more affected than the other. Its onset is usually at puberty, and is estimated to develop in 1 person per 20,000 people. While contact lenses can be used to maintain the regular shape of the cornea, in 5 to 10 percent of patients with keratoconus this will not give satisfactory results, and a corneal transplant is required. In Australia, it is the most common condition requiring a transplant, accounting for 31% of all transplants performed. It also has the highest success rate following transplantation, with 98.1% of transplanted corneas surviving the first year successfully, and 97.5% of grafts surviving past four years. Most recipients are between 20 - 45 years of age.

Bullous Keratopathy

Bullous keratopathy is a generic term for corneal oedema with the epithelium raised in blisters. It involves a loss of clarity and clouding over of the cornea, due to the gradual impairment of the endothelial cells responsible for keeping the cornea clear and healthy. It can occur for many reasons including hereditary susceptibility, previous eye surgery, or just simply advancing years. In Australia, it is the second most common condition requiring a transplant, accounting for 25% of all transplants performed. The success rate of a transplant for this condition, as measured by transplanted corneas surviving one year post-operatively, is 90.6%.

Success rates

Data from the Australian Corneal Graft Registry (one of the largest of its kind in the world) indicate that the Australian one year graft survival for all conditions is 91.2% decreasing to 80% at four years. Some conditions such as keratoconus have even higher success rates (98.1%).