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Corneal dystrophy is a term for a wide array of eye disorders that arise when particles build up on the cornea. Some forms of the condition are genetic. Many do not have any symptoms until later in life, when patients will experience pain, excessive tearing up, and gradual loss of vision.
Regular eye testing can detect the development of corneal dystrophy and signal to a doctor whether treatment is required or if the condition is asymptomatic enough to not require intervention.
Treatment can be as simple as applying eye drops or ointment. In severe cases, especially where pain or loss of vision is a factor, a patient might need a corneal transplant.
What Is Corneal Dystrophy?
Corneal dystrophy refers to a number of genetic, progressive eye disorders, characterized by the development and accumulation of abnormal material in the cornea (the transparent layer of the eye).
Some of the disorders that can be classified as corneal dystrophy might not cause any symptoms. Others can cause serious impairments to vision, hampering daily activities and requiring treatment.
The conditions of the development of corneal dystrophy, as well as the symptoms themselves, vary based on the kind of particular disorder. For example, the age of the patient when the abnormal material starts building up is different from one condition to another.
However, all forms of corneal dystrophy share some basic similarities.
- They tend to affect both eyes.
- Their progression is gradual.
- They affect only the eyes.
- There is a hereditary connection. A family history of corneal dystrophy can suggest the development of the condition in a patient.
What Does the Cornea Do?
To better understand what corneal dystrophy is and how it works, it helps to look at the parts and functions of the cornea itself.
The cornea has five layers.
- The epithelium is the outermost layer of the cornea, which acts as a protective shield.
- Bowman’s membrane, the second layer, is also used as a form of protection for the eye.
- The stroma is the thickest layer of the cornea. It contains water, collagen fibers, and other forms of connective tissue. Together, they give the cornea physical flexibility and strength.
- Descemet’s membrane is a strong, thinner inner layer.
- The endothelium is the final and innermost layer of the cornea. It contains special cells that move excess fluid out of the cornea.
All told, the cornea has two major functions: protecting the rest of the eye from dust, sand, germs, and other particles that can irritate the eye or cause actual harm; and acting as the outermost lens of the eye, taking incoming light rays and bending them onto the inner lens. Here, that light is sent to the retina (full of light-sensing cells at the back of the eye), which converts the light into images. These images are then sent along the optic nerve to the brain.
It is vital that the cornea remains clear and transparent in order to focus incoming light rays.
Recurrent Corneal Erosion
When outside material starts settling in at least one of the five layers of the cornea, this is the development of one of the forms of corneal dystrophies. It is possible for dust, dirt, sand, and germs to accumulate in multiple layers as well. When this happens, the cornea can lose its transparency, which in turn can cause blurred vision or a full loss of vision.
While the different forms of corneal dystrophy can cause distinct symptoms, one common sign of the condition is what is known as recurrent corneal erosion. As the Clinical Ophthalmology journal explains, the epithelium (the outermost layer of the cornea) does not properly stick to the eye. This can be a very uncomfortable or painful state. Patients with recurrent corneal erosion can suffer from an intense sensitivity to light, the feeling of something being stuck in the eye, and blurred vision.
Recurrent corneal erosion is therefore a typical characteristic of most presentations of corneal dystrophy.
A routine eye examination can detect the development of corneal dystrophy. A full clinical examination is the best way to get an accurate diagnosis. This process will entail a patient history, especially determining if the patient has a family history of corneal dystrophy, and testing, like a slit lamp examination. With a slit lamp exam, a special microscope (a slit lamp) gives a doctor a high degree of magnification to study the buildup of particles and discover whether they are affecting corneal functions.
Ophthalmology Times writes that certain genetic tests can diagnose the likelihood of specific corneal dystrophies developing, even before any symptoms present themselves.
Treating Corneal Dystrophy
How can corneal dystrophy be treated? Because there are many different types of the condition, treatment itself can vary.
People with asymptomatic corneal dystrophy (where there are no symptoms) or those who have mild symptoms might not require any treatment. Instead, it may be better for them to get regular checkups and examinations to see if the disease progresses to the point where treatment would be necessary.
Patients who require treatment might be given eye drops and ointments. For more serious cases, laser treatment and corneal transplants might be required. Recurrent corneal erosions (mentioned above) are usually dealt with via lubricating eye drops, antibiotics, ointments, or special contact lenses. If the erosions continue, a doctor might go a step further and perform corneal scraping or use excimer laser therapy, which can cut off abnormalities from the surface of the cornea (a procedure known as phototherapeutic keratectomy).
Patients who are in significant pain or suffering from vision loss might have to receive a corneal transplant. Also known as keratoplasties, these procedures are very effective in offering relief to patients who have advanced corneal dystrophy symptoms. Patients will likely have to continue receiving eye care for months after the procedure.
Types of Corneal Dystrophy
What are some of the different kinds of corneal dystrophy?
- Anterior corneal dystrophy: This form touches the outer layers of the cornea (the epithelium) and the Bowman membrane. It is also known as superficial corneal dystrophy, and it is one of the forms of the condition that is genetically passed on. Patients will feel pain, and their eyes will produce excessive tears. Anterior corneal dystrophy usually starts early in life, and it gets progressively worse as the patient ages.
- Epithelial basement membrane dystrophy: With this form of corneal dystrophy, very tiny dots form on the cornea’s epithelial. Together, these look like the lines of a fingerprint, and they are known as microcysts.
Most people who develop epithelial basement membrane dystrophy do not experience any symptoms. In those who do, however (about 10 percent of patients), the symptoms may include blurred vision as a result of recurrent erosions. As is typical of symptomatic corneal dystrophy, patients will experience a strong sensitivity to light and the feeling of something being on the surface of their eyes. This is a common form of corneal dystrophy.
- Reis-Bücklers corneal dystrophy: This is a genetic form of the condition that affects the Bowman membrane of the cornea. It can cause worsening scarring of the membrane and cloudy vision (opacity).
This form can strike early in a patient’s life, where they will experience recurrent erosions and resultant pain. By age 20, the patient will gradually lose vision in the affected eye as well as sensitivity to light.
Reis-Bücklers corneal dystrophy comes in two forms: granular corneal dystrophy type III and corneal dystrophy of Bowman's layer type I.
Stromal Corneal Dystrophies
A particular subset of corneal dystrophy is stromal corneal dystrophy, which affects the stroma (the central layer of the cornea). Some stromal corneal dystrophies can develop to the point where they affect more of the cornea’s layers.
Stromal corneal dystrophies are when the foreign particles accumulate on the stroma. An example of this is lattice corneal dystrophy, of which there are two main variants. What they both have in common is that the lesions that develop form branching lines that look like the overlapping crisscross of a lattice pattern or, at worse, cracked glass. In type 1 of this dystrophy, patients usually develop the lesions around age 10, preceded by painful recurrent corneal erosions.
Granular Corneal Dystrophy
A similar type of corneal dystrophy is granular corneal dystrophy type 1 because of the small particles that build up on the cornea that resemble breadcrumbs. These granules tend to develop between the ages of 20 and 30. Without treatment, they come together to form larger lesions.
Early on, granular corneal dystrophy type 1 usually doesn’t cause loss of vision. Without intervention, it may result in loss of vision by age 40. The sensitivity to light typical of corneal dystrophy is not universally felt by all people with this form of the condition, but eye pain is more common.
Type 2 of this form of corneal dystrophy entails lesions developing on the stroma by age 20. The obstructions on the cornea sometimes look like type 1 granular lesions and lattice lesions. As patients with this condition age, the lesions can grow to cover the entire stromal layer of the cornea. For some people, the cornea becomes so cloudy that they cannot see through the affected eye.
There are many other kinds of corneal dystrophies, but the key to detecting and treating them is the same. Regular eye testing and eye care can reduce the symptoms of the growth on the cornea. It can also provide doctors with enough time to intervene before the development of the dystrophies cause loss of vision.
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