What Are Corneal Dystrophies?
Corneal dystrophies are a group of relatively rare genetic eye disorders in which abnormal material often accumulates in the cornea — the clear, round dome covering the eye's iris and pupil. Most corneal dystrophies affect both eyes, progress slowly and run in families.
The cornea is made up of five layers:
- Epithelium: the outermost, protective layer of the cornea;
- Bowman membrane: this second protective layer is strong;
- Stroma: the thickest layer of the cornea. It is made up of water, collagen fibers and other connective tissue to strengthen the cornea and make it flexible and clear;
- Descemet membrane: a thin, strong inner layer that is also protective;
- Endothelium: the innermost layer made up of cells that pump excess water out of the cornea.
Corneal dystrophies are characterized by the accumulation of foreign material in one or more of the five layers of the cornea. The material may cause the cornea to lose its transparency, potentially causing loss of vision or blurred vision.
There are more than 20 different types of corneal dystrophies. They are generally grouped into three categories, depending on the part of the cornea that they affect:
- Anterior or superficial corneal dystrophies affect the outermost layers of the cornea: the epithelium and the Bowman membrane.
- Stromal corneal dystrophies affect the stroma, the middle and thickest layer of the cornea.
- Posterior corneal dystrophies affect the innermost parts of the cornea: the endothelium and the Descemet membrane. The most common posterior corneal dystrophy is Fuchs’ dystrophy, which is pictured above.