The cornea is the transparent, dome-shaped front surface of the eye, protecting inner structures and acting as the eye’s primary focusing lens. This clear tissue is composed of five distinct layers. Corneal dystrophy is a collective term for over 20 different inherited, progressive disorders. These conditions are characterized by the abnormal accumulation of material, such as protein or cholesterol, in one or more corneal layers. This buildup causes the cornea to lose transparency, leading to blurred vision and visual impairments.
What Patients Experience
The symptoms depend on which corneal layer is affected by the abnormal deposits. A common presentation is a gradual loss of visual clarity, often described as blurred or cloudy vision, as the cornea becomes opaque. The abnormal tissue formations also make it difficult for light to pass through, frequently causing light sensitivity (photophobia) and glare.
Patients with dystrophies affecting the outermost layer, the epithelium, often experience a painful “foreign body” sensation. This discomfort arises from recurrent corneal erosions, where the sensitive epithelial layer loosens or detaches from the underlying tissue. These erosions expose nerve endings, causing sudden, sharp pain that is often worse upon waking.
How Corneal Dystrophies Are Classified
Corneal dystrophies are classified based on the anatomical location of the abnormal material accumulation within the corneal layers. This system divides the conditions into three main groups: epithelial, stromal, and endothelial dystrophies. The location of the deposits directly impacts the symptoms and the required treatment.
Epithelial dystrophies affect the outermost protective layer, sometimes extending into the layer beneath it. Epithelial Basement Membrane Dystrophy (EBMD) is a well-known example, causing irregularities in the epithelium’s anchoring layer and often leading to recurrent corneal erosions. These superficial dystrophies primarily cause pain and foreign body sensation, though they can also cause blurriness.
Stromal dystrophies involve the stroma, the thickest, middle layer of the cornea, which is responsible for structural strength and clarity. Lattice corneal dystrophy (LCD) is characterized by fine, branching opacities that appear in a lattice pattern. Macular corneal dystrophy is distinguished by dense, grayish-white deposits that progressively cloud the entire stroma, often leading to severe sight loss by early adulthood.
Endothelial dystrophies affect the innermost layer, the endothelium, and its underlying Descemet’s membrane. The endothelium pumps excess fluid out of the stroma to maintain corneal transparency. Fuchs’ endothelial corneal dystrophy (FECD) is the most common posterior dystrophy, where endothelial cells die off and cannot be replaced. The resulting fluid buildup, known as corneal edema, causes the cornea to swell and thicken, leading to blurry vision that is worse in the morning.
Genetic Basis and Development
Corneal dystrophies are primarily genetic disorders inherited through a person’s family. Most forms are passed down through an autosomal dominant inheritance pattern. This means a child only needs to inherit one copy of the mutated gene from a single parent to develop the disorder.
The conditions often affect both eyes (bilateral) and are progressive, gradually worsening over years or decades. Specific genes have been identified, such as the TGFBI gene. Mutations in TGFBI are linked to several types of stromal and epithelial-stromal dystrophies, including Lattice and Granular corneal dystrophies.
The COL8A2 gene has been associated with early-onset Fuchs’ endothelial corneal dystrophy. The genetic mutation causes the body to produce abnormal proteins or prevents the normal maintenance of corneal tissue, leading to the characteristic buildup of insoluble material. The underlying cause is a cellular dysfunction due to a genetic abnormality.
Current Management and Treatment Options
Management begins with non-surgical methods focused on alleviating symptoms and preserving vision. For recurrent corneal erosions, conservative treatments include lubricating eye drops and ointments to keep the corneal surface smooth. Hypertonic saline solutions may be prescribed to draw excess fluid out of the cornea, especially in early endothelial dystrophies like Fuchs’.
A bandage contact lens can be worn as a protective layer over the epithelial surface, promoting healing and reducing pain from erosions. When deposits are superficial, phototherapeutic keratectomy (PTK) may be used. PTK uses an excimer laser to precisely remove thin layers of abnormal corneal tissue, which can improve visual acuity and reduce the frequency of erosions for some anterior dystrophies.
When the disease significantly impairs vision and non-surgical methods fail, corneal transplantation becomes necessary. Historically, penetrating keratoplasty (PKP) was the primary surgical option. This is a full-thickness transplant where the entire central cornea is removed and replaced with a donor cornea. PKP is now reserved for cases where damage affects all corneal layers.
Modern surgical techniques favor partial-thickness or lamellar keratoplasty, which replace only the diseased layer, preserving more of the eye’s natural structure. For Fuchs’ dystrophy and other endothelial failures, the procedures of choice are Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK) and Descemet’s Membrane Endothelial Keratoplasty (DMEK). These techniques involve removing only the diseased inner layer and transplanting a thin layer of healthy donor endothelium.
DMEK is considered the most advanced technique for endothelial dystrophies, offering the fastest visual recovery and the lowest risk of graft rejection. For stromal dystrophies that have not penetrated the deepest layer, Deep Anterior Lamellar Keratoplasty (DALK) can be performed. DALK replaces the diseased stroma while retaining the patient’s own healthy endothelium. These layer-specific transplants have improved outcomes, leading to less invasive surgery and a quicker return to clear vision.