What is Corneal Dystrophy?
Corneal dystrophy is a progressive eye disease that causes fluid or abnormal materials to build up in the cornea. The cornea forms part of the eye, covering the iris and pupil. It comprises transparent, protective layers (five in total) and helps focus light that reaches the lens.
If you have corneal dystrophy, there are problems in cellular function and development in one or both corneas. While it will rarely result in total blindness, it can lead to vision impairment and affect visual acuity (clarity).
The type of corneal dystrophy will vary depending on the layer of cornea it originates in. Symptoms may also appear.
However, some people who have corneal dystrophy may not notice any difference. For this reason, seeing an eye doctor and undergoing a comprehensive eye exam can rule out any eye disease.
Many corneal dystrophies can impact both eyes and are genetic diseases.
Types of Corneal Dystrophy
The cornea consists of five layers:
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Epithelium — this layer represents the outermost, protective layer of the cornea.
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Bowman’s membrane — following the epithelium, there is the second underlying layer.
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Stroma — the stroma will make up the thickest layer in the cornea. It is composed of water, collagen fibers, and other connective tissue. Its role is to support the cornea and make it flexible and transparent.
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Descemet’s membrane — this is another protective layer that is thin and strong.
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Endothelium — composed of cells that release accumulated water out of the cell, this layer is the innermost part of the cornea.
When a person experiences corneal dystrophy, the accumulation of material has occurred in one of the layers. While corneal dystrophy can be classified into many subtypes, there are three primary types of the eye disease.
Anterior
If you have anterior corneal dystrophy, this means you have the outermost layers of the cornea 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 (MDF) 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
The posterior corneal dystrophy refers to abnormalities in the corneal endothelium and Descemet membrane. When a person has this type of 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 Fuchs’ dystrophy?
Fuchs’ dystrophy is an eye condition that progresses over time. It will often appear in a person’s 30s or 40s. Although, in rare cases, the disease can arise during childhood.
You can subdivide symptoms of Fuchs’ dystrophy into two stages:
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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.
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Stage 2 (later stage) — in this phase, your vision does not improve as the day passes. You have accumulated too much fluid during sleep. Also, you will have tiny blisters on the cornea that could result in eye pain and other symptoms.
Treatment for this eye disease include:
- Eye drops
- Partial or complete corneal transplant
Is Corneal Dystrophy a Disability?
Corneal dystrophy may cause symptoms to appear. However, for some people, corneal dystrophy may go unnoticed in its beginning stages.
When the eye disease worsens, symptoms like blurriness or vision impairment can occur. If a person has a dramatic visual loss, corneal dystrophy could be considered as a disability.
Who is at Risk of Developing Corneal Dystrophy?
Some people may have a higher risk of developing corneal dystrophy than others.
Risk factors for corneal dystrophy include:
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Sex — Fuchs’ dystrophy will appear more often in females than in males. However, most corneal dystrophies will impact both males and females equally.
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Genetics — corneal dystrophies can run in the family, and specific genetic coding can determine which type of corneal dystrophy you’ll develop. If you have a family history of corneal dystrophy, it is essential to visit an eye clinic and seek a consultation.
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Age — corneal dystrophies, like Fuchs’ dystrophy, can occur in later stages of life, like the 30s or 40s. As you age, the risk of developing an eye condition increases.
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.
In contrast, genetic mutations lead to the accumulation of the deposits and possible visual impairments.
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 type of corneal dystrophy.
For example, if you have corneal dystrophy, you may report the following:
- Blurred vision
- Halos around light
- Trouble seeing at night
- Vision loss
- Clouding
Because these symptoms could overlap with those of other common eye conditions, including cataracts or glaucoma, you should undergo a comprehensive eye exam.
Your eye doctor will be able to examine your case and perform follow-up tests to rule out all other possible eye health issues.
Also, people with corneal dystrophy may experience corneal erosion. When the layer of cells on the epithelium (surface of the cornea) breaks away from the underlying layer (Bowman’s membrane), corneal erosion can lead to:
According to the National Institute of Health, the most common corneal dystrophy in the United States is keratoconus. This type of corneal dystrophy will affect 1 in every 2,000 Americans.
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.
Different treatments and surgical procedures are available to help manage corneal dystrophy.
When to See a Doctor
You should see an eye doctor if you have experienced any of the symptoms reported above. It is even more important to visit a specialist 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.
Currently, more than 20 types of corneal dystrophies have been identified.
How are Corneal Dystrophies Diagnosed?
If your ophthalmologist believes you have corneal dystrophy, you will undergo an eye examination and be asked about your family history of eye disease. Corneal dystrophy is an inheritable eye disease.
Furthermore, your eye doctor may use a slit lamp microscope to examine the front part of your eye. This tool beams a thin, bright sheet of light into the eye and will help assess for swelling or irregular bumps (guttae).
Other devices and tests like corneal tomography (to determine early signs of swelling) or corneal pachymetry (to measure corneal thickness) could form part of the eye examination.
A routine eye examination may be able to show corneal dystrophy. However, genetic testing may be necessary in some cases.
Corneal Dystrophy Treatment Options
If you have corneal dystrophy, treatment will vary based on two primary factors:
- The type of corneal dystrophy
- Symptom severity
Should you not have any symptoms, your eye care specialist may stay on the lookout for any possible disease progression. However, if you have symptoms, you may receive a prescription for eye drops or ointments. Laser treatments may also become an option.
In cases of corneal erosion, your eye doctor may treat the health problem with:
In more severe cases, you may have to consider phototherapeutic keratectomy (PTK) or even a corneal transplant (keratoplasty).
In the former, an eye surgeon performs an excimer laser surgical procedure to get rid of roughness or cloudiness from the cornea. This is important, because a non-transparent cornea does not focus the rays of light correctly on the retina.
When this happens, images become blurry, and vision suffers. In the latter, the eye surgeon removes damaged or unhealthy corneal tissue and places donor cornea tissue as a substitute.
A partial cornea transplant (otherwise known as an endothelial keratoplasty) is an option for endothelial dystrophies like Fuchs’ dystrophy.
