The cornea (the clear surface covering the eye) and the sclera (the white of the eye) are the only parts of the eye used for surgery.
The cornea, which is the eye’s main focusing element, is the clear surface covering the front of the eye. If the cornea is scarred by injury, infection, or disease, vision will be impaired. Fortunately, vision can be fully restored by a surgical procedure called corneal transplantation. This procedure entails removing a disc-shaped segment of an impaired cornea and replacing it with a similarly shaped piece of healthy cornea.
When the entire thickness of the cornea needs to be replaced, the impaired segment of the cornea is removed and a piece of donor cornea is sutured into place. This procedure is called Penetrating Keratoplasty (PKP).
When only the outer layers of the cornea need to be replaced, only these layers are shaved off and a corresponding partial thickness of donor cornea is sutured into place. This procedure is called Lamellar Keratoplasty (LKP).
Corneal transplantation is the most frequently performed human transplant procedure in North America. More than 90 per cent of corneal transplants restore sight. Unfortunately, supply does not keep up with demand. As a result, waiting lists are long and some people lose their sight before a cornea can be supplied.
The most common corneal diseases treated with corneal transplantation are Keratoconus, Bullous Kerathopathy, and Fuch’s dystrophy.
Keratoconus , a disease that affects young people primarily, causes the cornea to curve into a rounded “cone” shape. This abnormal curvature distorts the vision, but in many cases the cornea will stabilize without causing severe vision problems. However, if the disease progresses, the cornea becomes more peaked and vision deteriorates. Eventually, the centre of the cornea breaks and scars form.
Bullous Keratopathy causes the cornea to swell and blister. In its late stages, this disease becomes extremely painful.
Fuch’s dystrophy slowly destroys corneal cells. As the cells die, the cornea swells and vision becomes blurred and clouded. People with this disease compare their vision to looking through a shower curtain or waxed paper.
Sclera, the white part of the eye, is used for scleral patch grafts. Patch grafts a re used when the sclera has thinned and is in danger of breaking. When the sclera gets too thin, the eye changes shape and vision is distorted. If the sclera breaks, vision is lost completely. The graft is like patching a tire; it restores the eye to its proper shape so that it can function normally.
Sclera is also used to make prosthesis. The tissue, which has been wrapped around coral, is placed in the eye socket and attached to the eye muscles. An oculist paints a pupil and iris on a curved piece of porcelain-like material that is then placed over the sclera. Because the prosthesis moves in unison with the good eye, and also because the painted pupil and iris exactly match the recipient’s other eye, the prosthesis looks very natural.