Corneal dystrophy is a group of rare, inherited eye disorders that affect the cornea, the clear, dome-shaped outer layer. This condition is progressive, and typically affects both eyes symmetrically. It is characterized by the accumulation of abnormal materials within one or more of the cornea’s layers, causing a loss of transparency and affecting vision. Unlike infections or injuries, corneal dystrophy is non-inflammatory and is primarily driven by genetic mutations.
How the Cornea is Affected
The cornea acts as the eye’s primary lens and protective barrier, performing most of the focusing work to create a clear image on the retina. To maintain its transparency and focusing power, the cornea is structured into five main layers, each with a specialized function. The outermost layer, the epithelium, provides a smooth surface and protection, while the layer beneath it, Bowman’s layer, is a tough collagen sheet.
The thickest part is the stroma, which makes up nearly 90% of the cornea and consists of highly organized collagen fibers that ensure clarity and structural strength. Deeper still is Descemet’s membrane, which acts as a protective shield. The innermost layer is the endothelium, a single layer of specialized cells that functions like a pump, constantly removing excess fluid from the stroma to prevent swelling and maintain transparency.
Corneal dystrophies arise when a genetic mutation causes cells in one of these layers to produce or accumulate foreign, abnormal material. This buildup of debris—such as protein or cholesterol—disrupts the precise structure of the cornea. When the cornea loses its clarity, light is scattered instead of being sharply focused, leading to impaired vision.
Categorizing Corneal Dystrophies
Corneal dystrophies are categorized based on which of the five layers of the cornea is primarily affected by the abnormal deposits. The three main groups are epithelial and subepithelial, stromal, and endothelial dystrophies.
Epithelial and subepithelial dystrophies affect the outermost layers, the epithelium and Bowman’s layer. An example is Epithelial Basement Membrane Dystrophy, sometimes called Map-Dot-Fingerprint Dystrophy, which involves the formation of tiny dots, map-like patterns, and fingerprint-like lines on the corneal surface. These superficial changes can disrupt the smoothness of the cornea.
Stromal dystrophies involve the thick middle layer of the cornea, the stroma, where the deposits cause significant clouding and vision loss. Macular Dystrophy, a type of stromal dystrophy, is caused by the accumulation of abnormal glycosaminoglycans throughout the stroma. Another common type is Lattice Dystrophy, where amyloid protein deposits form fine, lattice-like lines in the stroma.
Endothelial dystrophies affect the innermost layer, the endothelium and Descemet’s membrane, impairing the fluid-pumping action of the endothelial cells. Fuchs’ Endothelial Dystrophy is the most common example in this category, leading to fluid buildup and swelling (edema) of the cornea. When the endothelium fails to pump water out, the stroma swells and becomes hazy.
Identifying Symptoms
The symptoms experienced by a patient depend heavily on which corneal layer is involved and the extent of the clouding. In the early stages, many corneal dystrophies may be asymptomatic, only being detected during a routine eye examination. As the condition progresses, the accumulation of material and loss of transparency begins to cause noticeable visual changes.
A common experience across many types of dystrophy is progressive blurring of vision. This is a direct result of the cloudy cornea scattering light and failing to focus images sharply. People with endothelial dystrophies, such as Fuchs’, often notice vision that is worse in the morning but improves slightly during the day as evaporation helps reduce corneal swelling.
Dystrophies that affect the surface layers, like epithelial types, frequently lead to painful recurrent corneal erosions. This occurs when the outermost epithelial layer fails to adhere properly to the underlying tissue and sloughs off, exposing sensitive nerve endings. These erosions can cause sharp pain, a feeling like grit or a foreign body is in the eye, and significant light sensitivity, known as photophobia.
Managing the Condition
Treatment is tailored to the severity of the symptoms. For mild or asymptomatic cases, doctors typically monitor the condition closely for signs of progression. When symptoms become bothersome, treatment starts with non-surgical options focused on symptom relief and maintaining corneal health.
Non-surgical approaches include lubricating eye drops and ointments to combat surface dryness and irritation. For patients with corneal swelling, particularly from endothelial issues, hypertonic saline drops or ointments containing a high salt concentration are used to draw excess fluid out of the cornea. When recurrent corneal erosions are present, a soft bandage contact lens may be applied to protect the exposed tissue and promote healing.
When vision loss becomes significant and cannot be corrected with drops or glasses, surgical intervention is considered. For full-thickness clouding, a Penetrating Keratoplasty (PK) removes the entire central portion of the diseased cornea and replaces it with clear donor tissue. Newer, selective transplant techniques are often preferred to replace only the damaged layers.
For endothelial dystrophies like Fuchs’, a partial transplant such as Descemet’s Stripping Endothelial Keratoplasty (DSEK) or Descemet’s Membrane Endothelial Keratoplasty (DMEK) is performed. These procedures replace only the diseased innermost layer, offering faster visual recovery and a lower risk of rejection compared to a full transplant. Deep Anterior Lamellar Keratoplasty (DALK) is a similar technique used for deep stromal dystrophies, replacing the cloudy stroma while preserving the patient’s own healthy endothelium.