Corneal Dystrophy · What Is It, Diagnosis, Treatment, and More

Corneal dystrophies (CD) refer to progressive conditions of the eye associated with the build-up of substances (e.g., proteins, lipids, amyloid) in one or more layers of the cornea. The cornea is the transparent front part of the eye, which consists of five distinct layers, each serving a crucial role in maintaining vision. The outermost layer of the cornea is the epithelium, acting as a protective barrier against external factors. Below the epithelium lies Bowman’s membrane, adding further resilience to the cornea. The stroma, the thickest and third layer, is primarily composed of water and collagen fibers, providing strength, refraction, and clarity while also allowing flexibility to the cornea. Descemet’s membrane, a thin but strong layer beneath the stroma, offers additional protection. Finally, the endothelium, the innermost layer, consists of cells responsible for regulating fluid balance within the cornea, ensuring optical clarity. The build-up of any substance in any of the above structures can lead to corneal dystrophy. 

Corneal dystrophies are grouped into three categories. Anterior or superficial corneal dystrophies, such as map-dot-fingerprint dystrophy, also called epithelial basement membrane dystrophy, affect the outermost layers of the cornea (i.e., the epithelium and Bowman’s membrane). Stromal corneal dystrophies, including lattice dystrophy, affect the stroma. Lastly, are posterior corneal dystrophies, which affect the innermost parts of the cornea (i.e., the endothelium and the Descemet membrane), such as Fuchs dystrophy.  

The causes of corneal dystrophies usually originate from genetic mutations affecting proteins involved in corneal structure and function. These mutations result in abnormal accumulation of lipids, proteins, or carbohydrates within the cornea, disrupting its transparency and smoothness. While the exact mechanisms underlying each type of corneal dystrophy may vary, inheritance patterns often follow autosomal dominance, meaning that only one copy of a mutated gene from either parent is sufficient to cause disease. There are autosomal recessive cases, in which two copies of a mutated gene, one from each parent, are required to cause some CDs as well. Some studies suggest that CD, particularly those with autosomal recessive inheritance patterns, can be more common in consanguineous families. 

Lisch epithelial CD and X-linked endothelial CD (XECD) are X-linked dominant diseases meaning that any mutation in just one copy of a gene on the X chromosome can cause CD. These X-linked disorders may be associated with other concomitantly inherited diseases, such as keratosis pilaris (i.e., benign condition causing dry, rough patches and tiny bumps on the skin), or congenital, inflammatory papules that result in hair loss. Environmental factors, such as UV exposure or eye trauma, may also influence disease progression in some cases. Additionally, certain corneal dystrophies, such as Fuchs dystrophy, may have multifactorial causes involving both genetic predisposition and other factors, such as aging, recurrent corneal erosion, or oxidative stress. 

Treatment for corneal dystrophy aims to alleviate symptoms, preserve vision, and address underlying causes whenever possible. Treatment plans for corneal dystrophy are individualized based on the type and severity of the condition, as well as the individual’s specific symptoms and needs. One common approach involves the use of medications, such as artificial tears and antibiotic eye drops or ointments, to manage symptoms like dryness, discomfort, or inflammation associated with the condition.  

Additionally, specialized soft contact lenses, such as rigid gas permeable or scleral lenses, may be prescribed to improve vision by masking irregularities in the corneal surface caused by dystrophy. In more advanced cases where vision loss is significant and other treatments prove ineffective, a corneal transplant (i.e., keratoplasty) may be necessary. This procedure involves replacing the damaged corneal tissue with healthy donor tissue to restore vision. 

Another treatment option is phototherapeutic keratectomy (PTK), a laser treatment that removes abnormal corneal tissue and smoothens the corneal surface. It can be beneficial for certain types of corneal dystrophies, particularly those affecting the outer layers of the cornea. Additionally, amniotic membrane transplantation may be utilized to promote corneal healing, reduce inflammation, and prevent scarring in some cases. 

Alongside medical interventions, symptomatic management through lifestyle modifications, such as wearing sunglasses to shield the eyes from UV radiation and avoiding eye rubbing, can also help alleviate symptoms and slow disease progression.

Emerging therapies are promising, with treatments such as enzyme therapy, gene therapy or RNA interference having positive results for targeting specific genetic forms of corneal dystrophy by addressing the defective enzymes or underlying genetic defects that lead to deposition of substances in the cornea.