Cogan's Dystrophy

Definition

Cogan's Dystrophy is a disorder of the eyes, specifically a type of corneal dystrophy. It is also called epithelial basement membrane dystrophy, Cogan's microcystic epithelial dystrophy, map-dot-fingerprint dystrophy or dystrophic recurrent erosion.

Cogan's Dystrophy affects the epithelial layer of the cornea in both eyes. The cells lose their attachments to the underlying Bowman's membrane and tend to tear away from the rest of the cornea causing pain, blurred vision and a red eye.

Description

The cornea is the transparent tissue that covers the front of the eye. Its function is two-fold: it shields the inside of the eye from dust, germs and other harmful matter and acts as the eye's outermost lens. When light strikes the cornea, it bends (refracts) the incoming light onto the crystalline lens. The lens then focuses the light onto the retina (the tissue at the back of the eye) that starts the translation of light into vision.

The tissue of the cornea is arranged in three layers: epithelium, stroma and endothelium.

The epithelium layer is the outermost region of the cornea. Its purpose is to block foreign matter from getting into the eye and provide a smooth surface that absorbs oxygen and other needed cell nutrients.

The stroma layer is behind the epithelium layer and gives the cornea its strength, elasticity, form and cells.

The endothelium layer is located between the stroma and the aqueous humor and its primary task is to pump excess water out of the stroma.

Causes and Risk Factors

There are many conditions that may affect the cornea. One such condition is corneal dystrophy. A corneal dystrophy is usually a bilateral, genetically transmitted disorder that affects the cornea. The cornea becomes opaque and often swollen due to accumulations of protein, fat, calcium and water (medically speaking - collagen, cytoplasmic debris, nuclear debris, lipids and fibrillogranular substances) that occur because of the dystrophy. Basically, the cornea loses its clarity, and the vision in the affected eye(s) is impaired.

To date there are 20 different types of corneal dystrophies, including Cogan's dystrophy.

Symptoms

The initial symptoms may include severe eye pain on waking in the morning, photophobia (intolerance to light), "something in my eye" sensation and slightly reduced visual perception. The reduced visual acuity is caused by opacities of the cornea resembling maps, dots and fingerprints, thus the name "map-dot-fingerprint dystrophy."

The epithelium has a map-like appearance (as if you were looking down on the earth and the opacities look like continents 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 look like small fingerprints.

Most people will never know that they have Cogan's dystrophy, since they will never have any pain and vision loss. For others, the disease will cause recurrent epithelial erosions that result in periodic blurred vision.

Diagnosis

Your physician will take a complete medical history and perform a physical examination focusing on the eye exam.

Treatment

Although Cogan's dystrophy rarely causes symptoms or reduces vision, the recurrent erosions require treatment. Depending on the severity, there are at least four treatment methods: hypertonic solution and/or patching, hypertonic solution and contact lens, corneal transplant (penetrating keratoplasty) and phototherapeutic keratectomy (PTK).

Hypertonic solution and/or patching

Eyedrops (hypertonic solution) are administered every 3 or 4 hours during the day and an ointment is used at night for mild cases. For other cases, double patching of the eye for 48 hours, followed by an ointment at bedtime for weeks to months.

In severe recurrent cases, it is usually effective to remove the redundant epithelium mechanically with a cotton tip applicator. This is done after instilling a topical anesthetic, followed by a cycloplegic (paralyzes the eye) and an antibiotic. Patch the eye for 48 hours.

Hypertonic solution and contact lens

In stubborn and recurrent cases the doctor may recommend the use of soft, loosely fitting, high-water-content contact lens in conjunction with eye drops.

Corneal transplant (penetrating keratoplasty)

A corneal transplant is done on an outpatient basis and lasts about an hour and a half. The patient is given a local anesthetic and light sedation. After the eye is numbed, an instrument similar to a cookie cutter is used to partially cut the cornea. The affected area (slightly smaller than the colored part of the eye) is removed and the new cornea is stitched on. The eye is then patched for the night. The stitches are kept in the eye for three to six months, and it takes up to a year to recover sharp vision.

Phototherapeutic keratectomy (PTK)

PTK may be an effective treatment in removing opacities from the superficial stroma, improving irregularities of the anterior surface of the cornea, and healing corneal epithelial defects.

Questions to Ask Your Doctor

Is this condition inherited? If so, should the children be tested for the condition?

Is this condition stabilizing or getting worse?

What treatment method do you recommend?

Will this condition recur after having surgery?