A corneal dystrophy is a rare genetic eye condition in which one or more parts of the clear outer layer of the eye (the cornea) lose their normal clarity as a result of a buildup of cloudy material. The general term corneal dystrophy refers to a group of corneal diseases.
There are many types of corneal dystrophies, and they are distinguished by the specific part or parts of the cornea affected.
The cornea comprises five layers: an outer layer (the epithelium), four middle layers (Dua’s layer, Bowman’s layer, the stroma, and Descemet’s membrane), and an inner layer (the endothelium).
These layers protect the eye from infectious or irritating material, and they serve as a refractive medium that bends incoming light toward the inner lens, where the light is directed to the retina, which converts it into images to be sent to the brain.
A cloudy cornea can interfere with the eye’s ability to focus incoming light, and thus may impair vision.
Some persons with corneal dystrophies may have no symptoms, whereas others may have significantly impaired vision. The specific symptoms can vary, depending on the type and the age at which the condition develops. However, there are several traits that all corneal dystrophies share:
- They are usually inherited
- They are bilateral (they affect the right and left eyes equally)
- They are not caused by outside factors, such as injury or diet
- Most progress gradually
- Most do not affect other areas of the body
- Most can occur in otherwise healthy people, male or female (except for Fuchs corneal dystrophy, which affects women about three times as often as men)
Common Symptoms of Corneal Dystrophy
Although a corneal dystrophy may not cause symptoms initially, there is always the possibility that it could in the future. The accumulation of scar tissue or foreign material in one or more of the layers of the cornea, which occurs with all dystrophies of the cornea, may cause it to lose its transparency, potentially causing loss of vision or blurred vision.
Most people with corneal dystrophies have variably-shaped corneal opacities in their corneas (an opacity is an area that is opaque—i.e., it cannot be seen through). These may be visible to the naked eye, but are more often detectable only by a doctor in the course of an eye examination.
Many forms of corneal dystrophy are characterized by recurrent corneal erosion. In this condition, the epithelium, the outermost layer of the cornea, continually fails to adhere to the eye properly.
People with recurrent corneal erosions may have discomfort or severe pain, an abnormal sensitivity to light (photophobia), the sensation of a foreign body (such as dirt or an eyelash) in the eye, or blurred vision.
Causes and Types of Corneal Dystrophy
Corneal dystrophy is an inherited genetic disease. Classification of corneal dystrophies is based on genetic, clinical, and pathologic information. Clinically, the corneal dystrophies can be divided into three groups, based on the anatomical location of the abnormalities. These three groups are:
Superficial Corneal Dystrophies:
- Meesmann dystrophy
- Reis-Bücklers corneal dystrophy
- Thiel-Behnke dystrophy
- Gelatinous drop-like corneal dystrophy
- Lisch epithelial corneal dystrophy
- Epithelial recurrent erosion dystrophy
- Subepithelial mucinous corneal dystrophy
Corneal Stromal Dystrophies:
- Macular corneal dystrophy
- Granular corneal dystrophy, type I
- The lattice corneal dystrophies
- Schnyder corneal dystrophy
- Fleck corneal dystrophy
- Congenital stromal corneal dystrophy
- Posterior amorphous corneal dystrophy
Posterior Corneal Dystrophies:
- Fuchs corneal dystrophy
- Posterior polymorphous corneal dystrophy
- Congenital hereditary endothelial corneal dystrophy
- X-linked endothelial corneal dystrophy
Diagnosis of Corneal Dystrophy — What to Expect During Your Trip to the Eye Doctor
Your doctor may find a corneal dystrophy incidentally during a routine eye examination. Your diagnosis will depend in part on the age at which your symptoms developed and the clinical appearance of your cornea when examined under a slit-lamp, a special microscope used to view the eye.
To confirm the diagnosis, your doctor will perform a clinical evaluation during which you will be asked to provide a detailed medical history — including your family medical history — and undergo a variety of tests. One test may involve removal of a piece of corneal tissue so that it can be examined.
Certain corneal dystrophies can be diagnosed with molecular genetic tests even before symptoms develop. Genetic counseling can usually be provided with detailed information about your particular corneal dystrophy.
Treating Corneal Dystrophy
How you are treated will depend on what type of corneal dystrophy you have, how severe your symptoms are, how far your disease has progressed, and your overall health and quality of life.
If you have no symptoms or only mild symptoms, your doctor may decide to postpone treatment and follow up with you regularly to watch the progression of the disease.
Conservative treatments for this condition may include eye drops and ointments. Recurrent corneal erosions may be treated with lubricating eye drops, hypertonic salt drops, ointments, antibiotics, or bandage contact lenses.
For recurrent corneal erosions that persist despite conservative treatment, your doctor may recommend corneal scraping or the use of excimer laser therapy, which can remove abnormalities from the surface of the cornea. This procedure is called phototherapeutic keratectomy.
If your symptoms are severe or advanced, a corneal transplant, also known as a keratoplasty, may be necessary. Although corneal transplants are effective for treating symptoms of corneal dystrophies, there is a risk that the donated (graft) cornea may eventually be affected by the disease.