Corneal Dystrophies

There are over 20 corneal dystrophies that affect all parts of the cornea. Some of the most common are:

Keratoconus

The disorder arises when the middle of the cornea thins and gradually bulges outward, forming a rounded cone shape. This abnormal curvature changes the cornea's refractive power, producing moderate to severe distortion (astigmatism) and blurriness (near- and farsightedness) of vision. These changes may also disrupt the normal, light-conducting arrangement of corneal protein, causing swelling and a sight-impairing scarring of the tissue.

Studies indicate that keratoconus stems from one of several causes: (1) an inherited corneal abnormality. About 7 percent of those with the condition have a family history of keratoconus; (2) an eye injury, i.e., excessive eye rubbing or wearing hard contact lenses for many years; (3) certain eye diseases, such as retinitis pigmentosa, retinopathy of prematurity, vernal keratoconjunctivitis; or (4) systemic diseases, such as Leber's congenital amaurosis, Ehlers-Danlos Syndrome, Down's syndrome, osteogenesis imperfecta, and Addison's disease.

Keratoconus usually occurs during puberty, or shortly thereafter. At first, people can correct their vision with eyeglasses. But as the astigmatism worsens, they must rely on specially fitted contact lenses to reduce the distortion and provide better vision. Finding a comfortable contact lens can be an extremely frustrating and difficult process. However, it is crucial because a poorly fitting lens could further damage the cornea and make wearing a contact lens intolerable.

In most cases, the cornea will stabilize after a few years without ever causing severe vision problems. But in about 10 to 20 percent of people with keratoconus, the cornea will eventually become too scarred or will not tolerate a contact lens. If either of these problems occur, a person will probably need to replace the diseased tissue with a donor cornea, called a corneal transplant.

This operation is successful in about 9 out of 10 people with advanced keratoconus. Several studies have also reported that about 80 percent of these patients have 20/40 vision or better with contact lenses after the operation. In fact, about 60 percent of transplant recipients will need to wear contact lenses after the surgery to correct astigmatism and nearsightedness.

For those with no scarring near the center of the cornea and 20/40 vision or better with contact lenses, another option is surgically grafting a layer of epithelial cells to flatten the cone-shaped cornea. This process is called epikeratophakia. It has comparable results to corneal transplantation and, if unsuccessful, it can be followed with corneal transplantation.

Map-Dot-Fingerprint Dystrophy

The epithelium is separated from the stroma, in part, by a membrane. It serves as the foundation on which the epithelial cells anchor and organize themselves. In map-dot-fingerprint dystrophy, the membrane develops abnormally. Like building a house on a damaged foundation, the epithelial cells anchor to an irregular membrane that, in turn, may make the epithelium slightly irregular.

The condition, which tends to occur in both eyes, usually affects adults between the ages of 40 and 70. It is also occasionally inherited--in which case it arises at about age 6.

Map-dot-fingerprint dystrophy gets its name from the unusual appearance of the cornea during an eye examination. Most often, the epithelium will have a map-like appearance, i.e., large, slightly cloudy bodies that look like a continent on a map. This configuration is actually the irregular pattern of the membrane extending into the epithelium. There may also be a sequence of opaque dots--formed from cellular debris--underneath or close to the map-like patches. Less frequently, the irregular membrane will form concentric lines in the central cornea that resemble small fingerprints.

Most people will never know that they have this corneal dystrophy, since they will never have any pain and vision loss.

But for others, the disease will cause recurrent epithelial erosions--possibly from poor epithelial adhesion to the membrane.

These erosions can be a chronic problem. They alter the cornea's normal curvature, causing periodic blurred vision. They may also expose the nerve endings that line the tissue, causing moderate to severe pain for several days. Generally, the pain will be worse in the morning. Other symptoms include: sensitivity to light, excessive tearing, and foreign body sensation in the eye.

Typically, the problem will flair up occasionally for a few years in adults and then go away on its own, with no lasting loss of vision.

However, if treatment is needed, the doctor will try to control the pain associated with the corneal erosion. He or she may do this by patching the eye to immobilize it or by prescribing lubricating eye drops and ointments. With effective care, the pain will subside in about 10 days, although periodic flashes of pain may occur for several weeks thereafter.

Fuch's Dystrophy

Fuch's dystrophy is a slowly progressing disease that usually affects both eyes and is slightly more common in women than in men. Although doctors can often see early signs of Fuch's dystrophy in people in their 30s and 40s, the disease rarely affects vision until a person reaches their 50s and 60s.

Fuch's dystrophy occurs when endothelial cells gradually deteriorate without any apparent reason, such as trauma or inflammation. As more endothelial cells are lost over the years, the cornea becomes less efficient at pumping water out of the stroma. This causes the cornea to swell and to distort vision. Eventually, the epithelium also takes on water, resulting in great pain and severe visual impairment.

Epithelial swelling damages vision in two ways: (1) changing the cornea's normal curvature, and (2) causing a sight-impairing haze to appear in the tissue. Epithelial swelling will also produce tiny blisters on the corneal surface. When the blisters burst, they are extremely painful.

At first, a person with Fuch's dystrophy will awaken with blurred vision that will gradually clear during the day. This occurs because the cornea is normally thicker in the morning, and it retains fluids during sleep that evaporate in the tear film while we are awake. But as the disease worsens, this swelling will remain constant and reduce vision throughout the day.

When treating the disease, doctors will try first to reduce the swelling with ointments or soft contact lenses. They may also instruct a person to use a hair dryer, held at arm's length or directed across the face, to dry out the epithelial blisters. This can be done two or three times per day.

But when the disease makes even the most simple tasks hard to complete, a person may need to consider having a corneal transplant to restore sight. The short-term success rate of corneal transplantation is quite good for people with Fuch's dystrophy. But, some studies do suggest that the long-term survival of the donor cornea can be a problem.

Lattice Dystrophy

Although lattice dystrophy can occur at any time in life, the condition usually arises in children between the ages of 2 and 7. It is characterized by an accumulation of abnormal protein fibers (amyloid) throughout the middle and anterior stroma. However, the disease is NOT related to amyloidosis, a serious systemic disease.

Lattice dystrophy gets its name from the amyloid deposits, which during an eye examination can appear as clear, comma-shaped dots and branching filaments that overlap each other in the stroma, creating a lattice effect. Over time, the lattice lines will grow opaque and involve more of the stroma. They will also gradually coalesce, giving the cornea a slight cloudiness that may also reduce vision somewhat.

In some people, abnormal protein also accumulates under the epithelium. This may result in poor adhesion between the stroma and epithelium, causing periodic epithelial erosions. The erosion will: (1) alter the cornea's normal curvature, resulting in temporary vision problems such as astigmatism and nearsightedness, and (2) expose the nerves that line the cornea, causing severe pain. In fact, even the involuntary act of blinking can be painful.

To ease this pain, a doctor may prescribe eye drops and ointments to reduce the friction on the eroded cornea. In some cases, an eye patch may be used to immobilize the eye. With effective care, the pain will subside in about 10 days, although occasional sensations of pain may occur for about the next 6 to 8 weeks.

By about age 40, some people will have scarring under the epithelium. As a result, a haze will develop on the cornea that can greatly obscure a person's vision. In this case, a corneal transplant may be needed. Patients with lattice dystrophy have an excellent chance for a successful transplant with good vision. However, in as little as three years, lattice dystrophy may also arise in the donor cornea. In one study, in fact, about half of the transplant patients with lattice dystrophy had a recurrence of the disease from 2 to 26 years after the operation. Of these, 15 percent required a second corneal transplant.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.