Corneal dystrophies

Corneal dystrophy is a hereditary genetic disease that affects the cornea, the circular transparent wall in the anterior part of the eye. It usually affects the central part of the cornea of both eyes without causing eye inflammation in patients between the age of 10 and 40 and progresses slowly.  

A mutation of chromosones is the cause of this disease, which is why, the presence of this disease in a family, in particular in a patient's close family, is a risk factor. This mutation leads to an accumulation of materials or substances that should not be found in the cornea. This disease has not been associated with environmental factors or other systemic diseases. 

The types of corneal dystrophy are classified according to the layer of the cornea that is affected: 

• Meesmann epithelial corneal dystrophy and Cogan fingerprint lines, geographic map-like lines and dots are dystrophies that affect the epithelial layer, the most superficial layer of the cornea. Reis-Bücklers corneal dystrophy and Thiel-Behnke corneal dystrophy affect the the Bowman's membrane, between the epithelium and the most profound layers.   
• Stromal dystrophies affect the stroma of the cornea, the thickest layer. The most common are Groenouw type I corneal dystrophy, Groenouw type II macular dystrophy and reticular distrophy, etc.
• The endothelial distrophies and Descemet's membrane are changes to the most profound layers. Fuchs endothelial corneal dystrophy is one of the most common. 

The symptoms of patients with corneal dystrophy are very varied. Many do not have any symptoms, especially at the start of the disease. Patients whose most superficial layers are affected usually develop epithelial recurrent erosion leading to irritation and eye pain in the morning which comes and goes. 

However, patients with stromal dystrophy usually have reduced visual acuity because of anomalous substance deposits in the central area of the cornea. A loss of vision is also the main symptom in patients with endothelial dystrophies. 

However, in this group of patients, reduced vision is due to the poor functioning of the endothelial cells whose role is to prevent excess liquid in the cornea and thus maintain its transparency. As a result of the cellular change in this layer, the excess liquid penetrates the cornea causing a corneal oedema (swollen cornea due to liquid retention) leading to its loss of transparency and a reduction of visual acuity. 

At present, there is no effective means of preventing this disease. In the future, genetic engineering may be a useful tool for changing and standardising the mutated chromosones that cause this disease.

Treatment for corneal dystrophy depends on its type, the symptoms of the patient and its severity. 

Patients who are symptomless do not require treatment. 

Patients with recuring erosions are treated with lubricating eyedrops and ointments, therapeutic contact lenses or a PTK excimer laser depending on the severity of the eroision and the response to each treatment. 

Patients with a significant loss of vision due to materials or anomalous substances deposits in the stroma require a cornea transplant, either a full cornea transplant (penetrating keratoplasty) or just the most anterior layers (deep lamellar keratoplasty).

In patients with an accumulation of liquid in the cornea due to poorly functioning endothelial cells, the treatment involves hypersmolar eyedrops and ointments at the early stages of the disease. If the reduction in visual acuity continues and restricts the patient's daily activities, one option would be a cornea transplant, be it a full-thickness transplant or just the endothelial cells (posterior keratoplasty).