Corneal dystrophies represent a group of inherited eye disorders characterized by the accumulation of abnormal material within the cornea. The cornea, the transparent front window of the eye, plays an important role in focusing light onto the retina, allowing for clear vision. When affected by dystrophy, this normally clear tissue gradually loses its transparency, leading to impaired sight. These conditions are progressive and affect both eyes, stemming from genetic factors.
Causes and Genetic Links
Corneal dystrophies primarily arise from gene mutations that affect corneal structure and function. Many of these conditions are inherited in an autosomal dominant pattern. This means inheriting one altered gene copy from either parent is sufficient for the disorder to develop, with a 50% chance of inheritance if one parent carries the mutation.
Several different genes have been identified in relation to various corneal dystrophies. For instance, mutations in the TGFBI gene are commonly associated with several stromal dystrophies, while changes in the SLC4A11 gene can lead to posterior polymorphous corneal dystrophy. While most cases have a clear family history, some rare instances occur spontaneously without a known genetic link.
Classification and Common Types
Corneal dystrophies are categorized based on which specific layer of the cornea is primarily affected by abnormal material accumulation. This anatomical classification helps in understanding their distinct characteristics and progression.
Anterior Dystrophies
These dystrophies affect the outermost corneal layers: the epithelium and Bowman’s layer. Epithelial Basement Membrane Dystrophy (EBMD), also known as Map-Dot-Fingerprint Dystrophy, is a common example. In EBMD, the epithelial cells do not adhere properly to the underlying basement membrane, leading to recurrent erosions and an irregular corneal surface. This can cause blurred vision or discomfort, especially upon waking.
Stromal Dystrophies
Stromal dystrophies affect the stroma, the thickest middle layer. Lattice Dystrophy involves the buildup of amyloid protein fibers, forming branching, lattice-like lines within the stroma. Granular Dystrophy, another stromal type, is characterized by the accumulation of hyaline material, appearing as distinct, breadcrumb-like deposits. Both can cause progressive vision loss from increasing corneal clouding.
Posterior Dystrophies
These conditions involve the innermost layers of the cornea: Descemet’s membrane and the endothelium. Fuchs’ Endothelial Corneal Dystrophy is a common posterior dystrophy where the endothelial cells, which pump fluid out of the cornea to maintain clarity, gradually die off. This cell loss leads to fluid accumulation, causing corneal swelling and haziness. It often manifests with early morning blurry vision that improves throughout the day as fluid evaporates.
Recognizing the Symptoms
The symptoms experienced by individuals with corneal dystrophies vary depending on the specific type and progression stage. A common early sign is gradual blurring or clouding of vision, which may initially be subtle but worsens over time. Light sensitivity (photophobia) often develops, making bright environments uncomfortable.
Patients may also experience glare, especially around lights at night, due to light scattering by abnormal corneal tissue. Eye pain or irritation can occur, especially with anterior dystrophies causing recurrent corneal erosions. Some individuals report a persistent sensation of having a foreign object in the eye. These symptoms can affect daily activities and quality of life.
Diagnostic Process
Diagnosing corneal dystrophies begins with a comprehensive eye examination and a detailed medical and family history. The ophthalmologist inquires about visual changes, pain, and family history of similar eye conditions. Visual acuity is tested to assess vision impairment.
The slit-lamp exam is a key diagnostic tool, allowing the eye doctor to view corneal layers under high magnification. This exam identifies characteristic deposits, opacities, or irregularities specific to dystrophy types. Additional tests include corneal pachymetry, which measures corneal thickness, particularly for monitoring Fuchs’ dystrophy. Corneal topography maps the corneal surface curvature. Genetic testing can confirm specific gene mutations, aiding precise diagnosis and family counseling.
Management and Treatment Approaches
Management of corneal dystrophies aims to alleviate symptoms, prevent complications, and restore vision. Non-surgical approaches are often the first treatment for milder symptoms. Lubricating eye drops and ointments manage dryness and irritation. Hypertonic saline drops or ointments can draw excess fluid from the cornea in conditions like Fuchs’ dystrophy, reducing swelling. Bandage contact lenses may be prescribed to protect the corneal surface and relieve pain from recurrent erosions in anterior dystrophies.
When vision becomes significantly impaired and conservative measures are no longer sufficient, surgical interventions are considered. Phototherapeutic Keratectomy (PTK) is a laser procedure used primarily for anterior dystrophies, smoothing the corneal surface and removing superficial abnormal tissue. For advanced cases affecting deeper layers, corneal transplant (keratoplasty) becomes necessary, replacing diseased tissue with healthy donor tissue. Full-thickness transplants (Penetrating Keratoplasty or PK) replace all corneal layers. More targeted partial-thickness transplants, such as Descemet’s Membrane Endothelial Keratoplasty (DMEK) or Descemet’s Stripping Endothelial Keratoplasty (DSEK), replace only affected inner layers, commonly used for posterior dystrophies like Fuchs’.