Corneal Dystrophy

What is Corneal Dystrophy?

Corneal dystrophies are a group of rare genetic diseases that affect the eye's cornea. The cornea is at the front of the eye, covering the iris and pupil.

Corneal dystrophy involves problems with the corneal cells in one or both corneas. While it rarely results in total blindness, it can impair vision and affect visual acuity (clarity). 

Most corneal dystrophies occur in both eyes and progress slowly. The type of corneal dystrophy will vary depending on the layer of the cornea it originates in.

Layers of the Cornea

Corneal dystrophies can involve an accumulation of foreign material in one or more layers of the cornea. This can lead to blurry vision and decreased vision. 

The cornea consists of five layers:

• Epithelium. The outermost layer serves to protect the cornea. 
• Bowman’s membrane. A protective membrane beneath the epithelial layer. 
• Stroma. The thickest layer of the cornea. It’s composed of water, collagen fibers, and other connective tissue. It provides support and flexibility to the cornea. 
• Descemet’s membrane. A thin, strong, protective layer. 
• Endothelium. The innermost layer comprises cells that move excess water out of the cornea.

Types of Corneal Dystrophy

While corneal dystrophy can be classified into more than 20 subtypes, there are three primary types of eye disease. 

Anterior

If you have anterior corneal dystrophy, the outermost layers of the cornea are affected. These layers include the epithelium and Bowman’s membrane.

Examples of this type of corneal disease include:

• Epithelial basement membrane dystrophy (EBMD), also called anterior basement membrane dystrophy (ABMD) or map-dot-fingerprint dystrophy
• Meesmann dystrophy
• Reis-Bucklers dystrophy
• Thiel-Behnke dystrophy 

Stromal

Stromal corneal dystrophies primarily impact the stroma. However, the condition can expand to anterior corneal layers and involve Descemet’s membrane and the endothelium.

According to the International Committee for Classification of Corneal Dystrophies (IC3D), there are many different subsets of stromal corneal dystrophies, including:

• Lattice corneal dystrophy type 1 
• Lattice corneal dystrophy type 2
• Granular corneal dystrophy type 1  
• Granular corneal dystrophy type 2 (Avellino corneal dystrophy)
• Macular corneal dystrophy 
• Schnyder corneal dystrophy 
• Congenital stromal corneal dystrophy
• Fleck corneal dystrophy 

Posterior

Posterior corneal dystrophy involves abnormalities in the corneal endothelium and Descemet membrane. When a person has this corneal dystrophy, excess fluid (edema) occurs, and visual acuity decreases.

Examples of posterior corneal dystrophy include:

• Posterior polymorphous corneal dystrophy (PPCD)
• Congenital hereditary endothelial corneal dystrophy (CHED) 
• X-linked endothelial corneal dystrophy (XECD)
• Fuchs’ corneal dystrophy 

What Is Keratoconus?

Keratoconus is the most common corneal dystrophy in the U.S.² It affects the lower and middle layer of the cornea and is usually diagnosed in teenagers and young adults.

A normal cornea is round. Keratoconus causes the cornea to bulge outward into a cone shape. This change in the shape of the cornea can cause vision problems. 

Symptoms of keratoconus include:

• Double vision
• Blurry vision
• Itchy eyes
• Nearsightedness (myopia)
• Astigmatism 
• Abnormal sensitivity to light

What is Fuchs’ dystrophy?

Fuchs’ corneal dystrophy is common among posterior corneal dystrophies. It will often occur in your 30s and 40s and progress over time. Vision problems don’t usually appear until you reach your 50s. 

Fuchs’ dystrophy affects women more than men. In rare cases, the disease can arise during childhood.

You can subdivide symptoms of Fuchs’ dystrophy into two stages:

• Stage 1 (early stage). In this phase, you may experience only a few, if any, symptoms. When you wake up, your vision may be hazy or blurry. It will gradually improve as the day passes.
• Stage 2 (later stage). In this phase, your vision doesn’t improve as the day passes. You have accumulated too much fluid during sleep. Tiny blisters on the cornea may cause eye pain and other symptoms. 

What are the Signs & Symptoms of Corneal Dystrophy?

If you have corneal dystrophy, you can experience some symptoms. These symptoms may not always be present and could vary according to the corneal dystrophy type. 

Signs and symptoms of various corneal dystrophies include:

• Blurred vision 
• Halos around light
• Trouble seeing at night 
• Vision loss
• Clouding

These symptoms could overlap with other common eye conditions, including cataracts or glaucoma. A comprehensive eye exam is essential to rule out all other possible eye health issues.

Corneal Erosions 

People with corneal dystrophy may experience corneal erosions. This happens when the layer of cells on the corneal epithelium (surface layer) breaks away from the underlying layer (Bowman’s membrane).

Recurrent corneal erosions can lead to:

• Mild to severe eye pain
• Sensitivity to light
• A sensation of something lodged in the eye (foreign body sensation)

What Causes Corneal Dystrophy?

Corneal dystrophies occur because deposits progressively build up within a layer (or multiple layers) of the cornea. Issues like inflammation, infection, or trauma do not cause corneal dystrophies.

Corneal dystrophies tend to run in families. Inherited genetic mutations lead to the accumulation of deposits and possible visual impairments. 

Who is at Risk of Developing Corneal Dystrophy?

Some people may have a higher risk of developing corneal dystrophy than others. Risk factors include:

• Sex. Fuchs’ dystrophy will appear more often in females than in males. However, most corneal dystrophies impact males and females equally. 
• Genetics. Corneal dystrophies can run in the family, and specific genetic coding can determine which type of corneal dystrophy you’ll develop. 
• Age. Corneal dystrophies often occur in the 30s or 40s. As you age, the risk of developing an eye condition increases. 

Is Corneal Dystrophy a Disability?

Corneal dystrophy could be considered a disability for people who experience significant visual impairment.

Many people with early stages of corneal dystrophy don't notice any symptoms. People who develop symptoms early on may only experience eye discomfort. 

Symptoms like blurriness or vision impairment can occur when the eye disease worsens. 

Can Corneal Dystrophy Cause Blindness?

Corneal dystrophy can cause visual impairments due to vision loss. However, it is not typical for this eye condition to cause total blindness.

Treatments and surgical procedures, such as a corneal transplant, are available to help manage these conditions. 

When to See a Doctor 

You should see an eye doctor if you experience symptoms of corneal dystrophy. Visiting a specialist is even more critical if those symptoms worsen over time.

Because symptoms of corneal dystrophy can overlap with those of other eye conditions, your eye doctor may refer you to a corneal specialist. This eye care professional will perform a differential diagnosis and rule out all other eye conditions.

If symptoms appear suddenly, you should call for an immediate appointment. Some eye conditions may need prompt treatment.

How are Corneal Dystrophies Diagnosed?

If your ophthalmologist believes you have corneal dystrophy, they will perform an eye examination. They will review your symptoms and ask about your family history of eye disease because corneal dystrophy is inheritable.

Tests to help diagnose corneal dystrophy include:

• Slit lamp microscope exam. This microscope beams a thin, bright sheet of light into the eye and will help your doctor assess corneal swelling or irregular bumps (guttae).
• Corneal tomography and topography. A special photograph of your cornea to look for early signs of swelling.
• Corneal pachymetry. This test measures corneal thickness.

Genetic testing may be necessary in some cases. 

Corneal Dystrophy Treatment Options

Treatment for corneal dystrophy depends on your type and the severity of your symptoms. 

Should you not have any symptoms, your eye care specialist may stay on the lookout for any possible disease progression. 

If you have symptoms, you may receive one or more of the following treatments:

Nonsurgical Treatments 

Nonsurgical treatment for corneal dystrophy includes medications and other therapies to relieve symptoms and reduce swelling. 

Options include:

• Prescription eye drops or ointments
• Corneal transplant (keratoplasty)
• Special soft contact lenses to relieve pain

In cases of corneal erosion, your eye doctor may prescribe:

• Antibiotics
• Lubricating eye drops
• Ointments
• Special protective soft contact lenses

Laser Treatment

Laser treatment may be an option if medications and other therapies fail to improve your symptoms. Phototherapeutic keratectomy (PTK) is an excimer laser surgical procedure to remove roughness or cloudiness from the cornea. 

This is important because a non-transparent cornea does not correctly focus the rays of light on the retina. When this happens, images become blurry, and vision suffers.

Corneal Transplant Surgery

If you have severe vision problems, your doctor may recommend full or partial corneal transplant surgery. Corneal transplant (keratoplasty) removes damaged or unhealthy corneal tissue and replaces donor cornea tissue.

A partial cornea transplant (an endothelial keratoplasty) is an option for endothelial dystrophies like Fuchs’ dystrophy.

Summary 

Corneal dystrophies are rare genetic diseases. They cause abnormal material to build up in the cornea, the transparent tissue at the front of the eye.

There are more than 20 types of corneal dystrophies. The type you have depends on the layer of the cornea affected. 

Corneal dystrophy symptoms include sensitivity to light, blurry vision, and decreased vision. It's essential to see a doctor for an accurate diagnosis and treatment. In severe cases, corneal dystrophies are treatable with medications, special contact lenses, and laser surgery or corneal transplants.