Corneal Disease

A Corneal Transplant or Penetrating Keratoplasty (PKP) is the procedure used to replace a scarred or damaged cornea.

What is Corneal Disease?

Corneal and external diseases involve the cornea, anterior chamber of the eye, iris, lens, conjunctiva and eyelids.
 
These diseases include:

• Cataracts
• Corneal allergies
• Infections and irregularities
• Refractive errors (nearsightedness, farsightedness and astigmatism)
• Conjunctivitis (pink eye)
• Dry eye
• Tear disorders
• Keratoconus, pterygium, endophthalmitis, Fuch’s Dystrophy and others

What is the cornea?

The cornea is the transparent, dome-shaped, outermost layer that covers the iris and pupil in the front of the eye.
 
Although the cornea is clear, it contains a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor that fill the chamber behind it.
 
As one of the protective layers of the eye, the cornea serves two functions:

• First, along with the eyelid, eye socket, sclera (white part of the eye), and the tear film, the cornea shields the eye from dust, germs, and other harmful matter.

• Second, as the eye’s outermost lens, it is the entry point for light into the eye. When light strikes the cornea, it bends, or refracts, the incoming light onto the lens. The lens further refocuses the light onto the retina, a layer of light-sensing cells lining the back of the eye.

 
To see clearly, the cornea and lens must focus the light rays precisely on the retina. This refractive process is similar to the way a camera takes a picture. You could say the cornea and lens in the eye act like a camera’s lens, with the retina being the film. If the cornea is unable to focus the light properly, the retina receives a blurry image.

What injuries or conditions affect the cornea?

Projectile foreign bodies, lacerations and blunt trauma can cause scarring that clouds the cornea. Hereditary conditions including degenerations and dystrophies may also cloud the cornea.
 
The most common hereditary condition seen in young people is keratoconus, a condition in which the cornea assumes a cone shape. This is common in children with Down’s syndrome and in people with allergic conjunctivitis. These patients may be able to use contact lenses or glasses for a period of time, but may eventually develop scarring and high astigmatism that cannot be corrected without a corneal transplant.
 
Occasionally, it may become necessary to perform a corneal transplant following cataract surgery if bullous keratopathy occurs. Bullous keratopathy is a condition where the endothelial cells on the back of the cornea decrease in number after cataract surgery. However, this is less common today because of new techniques and improved lens design.

How can the cornea become damaged?

The eye surface can be severely damaged in a number of ways, including:

• Chemical and thermal injuries
• Pathological diseases such as Stevens-Johnson syndrome and pemphigoid
• Chronic infections or inflammations
• New tissue growths such as pterygium (thought to be related to sun damage) and tumours
• Neurotrophic conditions (due to damage to the eye’s sensory nerves)
• Rare hereditary conditions such as aniridia (congenital absence of the iris)

These problems can result in extensive damage on the eye surface, leading to new blood vessel formation and scarring. This is damage which can result in loss of vision.