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What is Cornea

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Córnea

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The clear, dome-shaped window of the front of your eye. It focuses light into your eye.

What Causes Cornea Problems?

Eye disease and injuries can damage the cornea. Here are some common eye problems that can lead to a damaged cornea:
o Keratoconus, where the cornea is coneshaped rather than dome-shaped
o Fuchs’ dystrophy, where cells in the inner layer of the cornea are not working effectively
o Eye infections or injuries that scar the cornea
o Previous corneal surgery or other eye surgery that damaged the cornea

What Are Corneal Dystrophies?

Corneal dystrophies are a group of rare genetic eye disorders. With corneal dystrophies, abnormal material builds up in the cornea (the clear, front window of the eye). Most corneal ystrophies affect both eyes. They progress slowly and run in families.

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The cornea has five layers:
o Epithelium: the outermost, protective layer of the cornea.
o Bowman’s membrane: this second protective layer is strong.
o Stroma: the thickest layer of the cornea. It is made up of water, collagen fibers and other connective tissue. This strengthens the cornea and makes it flexible and clear.
o Descemet’s membrane: a thin, strong inner layer that is also protective.
o Endothelium: the innermost layer made up of cells that pump excess water out of the cornea.
Corneal dystrophies are caused by the build-up of foreign material in one or more of the five layers of the cornea. The material may cause the cornea to lose its transparency. This can cause loss of vision or blurred vision.
There are more than 20 different types of corneal dystrophies. They are generally grouped into three categories:
o Anterior or superficial corneal dystrophies. These affect the outermost layers of the cornea: the epithelium and Bowman’s membrane.
o Stromal corneal dystrophies affect the stroma, which is the middle and thickest layer of the cornea.
o Posterior corneal dystrophies affect the innermost parts of the cornea: the endothelium and the Descemet membrane. The most common posterior corneal dystrophy is Fuchs’ dystrophy.

What are symptoms of corneal dystrophy?

The symptoms of corneal dystrophy depend upon the type of corneal dystrophy. Some people experience no symptoms. In others, the build-up of material in the cornea causes it to become opaque (not clear). This leads to blurred vision or vision loss.
Many people also experience corneal erosion. This happens when the layer of cells on the surface of the cornea (the epithelium) loosens from the layer underneath (Bowman’s membrane). 

Corneal erosion causes:
o mild to severe pain in the eye
o light sensitivity
o feeling like something is in the eye

Who is at risk for corneal dystrophies?

Because most corneal dystrophies are genetic, family history of the disease increases your risk. Corneal dystrophies can appear at any age. Men and women are equally affected by most corneal dystrophies, except for Fuchs’ dystrophy. Fuchs’ affects women more frequently than men.

Corneal Dystrophy Diagnosis and Treatment

If your ophthalmologist thinks you have a corneal dystrophy, they will examine your eye. They will also ask about your family history of eye disease.

Your ophthalmologist will use a slit lamp microscope to shine a thin, bright sheet of light into your eye. This helps the doctor examine the front part of your eye thoroughly. If someone has no symptoms, a routine eye examination may show that they have corneal dystrophies. In some cases, genetic testing can identify corneal dystrophies.

How is corneal dystrophy treated?

Treatment for corneal dystrophies depends on:
o the type of dystrophy, and
o the severity of symptoms

If you do not have any symptoms, your ophthalmologist may monitor your eyes closely to see if the disorder is progressing. In other cases, eye drops, ointments or laser treatment may be appropriate. In many cases, people with corneal dystrophy will have repeat corneal erosion.

This condition may be treated with:
o antibiotics
o lubricating eye drops
o ointments
o or special soft contact lenses that protect the cornea

If erosion continues, other treatment options may include the use of laser therapy or a technique for scraping the cornea. In more severe cases, a corneal transplant (called keratoplasty) may be necessary. The damaged or unhealthy corneal tissue is removed, and clear donor cornea tissue is put in its place. For endothelial dystrophies, such as Fuchs’ dystrophy, a partial cornea transplant (or endothelial keratoplasty) is used.

About Corneal Transplantation

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The cornea is the clear, front window of the eye. It helps focus light into the eye so that you can see. The cornea is made of layers of cells. These layers work together to protect your eye and provide clear vision. Your cornea must be clear, smooth and healthy for good vision. If it is scarred, swollen, or damaged, light is not focused properly into the eye. As a result, your vision is blurry or you see glare.

If your cornea cannot be healed or repaired, your ophthalmologist may recommend a corneal transplant. This is when the diseased cornea is replaced with a clear, healthy cornea from a human donor. A human donor is someone who chooses to donate (give) his or her corneas after their death to people who need them. All donated corneas are carefully tested to make sure they are healthy and safe to use. There are different types of corneal transplants. In some cases, only the front and middle layers of the cornea are replaced. In others, only the inner layer is removed. Sometimes, the entire cornea needs to be replaced.

Corneal Transplant Surgery Options

Full thickness corneal transplant:

Your entire cornea may need to be replaced if both the front and inner corneal layers are damaged. This is called penetrating keratoplasty (PK), or full thickness corneal transplant. Your diseased or damaged cornea is removed. Then the clear donor cornea is sewn into place.

PK has a longer recovery period than other types of corneal transplants. Getting complete vision back after PK may take up to 1 year or longer. With a PK, there is a slightly higher risk than with other types of corneal transplants that the cornea will be rejected. This is when the body’s immune system attacks the new cornea tissue.

Partial thickness corneal transplant:

Sometimes the front and middle layers of the cornea are damaged. In this case, only those layers are removed. The endothelial layer, or the thin back layer, is kept in place. This transplant is called deep anterior lamellar keratoplasty (DALK) or partial thickness corneal transplant. DALK is commonly used to treat keratoconus or bulging of the cornea.

Healing time after DALK is shorter than after a full corneal transplant. There is also less risk of having the new cornea rejected.

Endothelial keratoplasty:

In some eye conditions, the innermost layer of the cornea called the “endothelium” is damaged. This causes the cornea to swell, affecting your vision. Endothelial keratoplasty is a surgery to replace this layer of the cornea with healthy donor tissue. It is known as a partial transplant since only this inner layer of tissue is replaced.

There are a few types of endothelial keratoplasty. They are known as:

o DSEK (or DSAEK) — Descemet’s Stripping (Automated) Endothelial Keratoplasty
o DMEK — Descemet’s Membrane Endothelial Keratoplasty

Each type removes damaged cells from an inner layer of the cornea called Descemet’s membrane. The damaged corneal layer is removed through a small incision. Then the new tissue is put in place. Just a few stitches—if any—are needed to close the incision. Much of the cornea is left untouched. This lowers the risk of having the new cornea cells being rejected after surgery.

Some things to know:
o With DSEK/DSAEK surgery, the donor tissue may be easier to transplant and position because it is thicker than the donor tissue in DMEK surgery.
o In DMEK surgery, the donor tissue is thin and can be more difficult to transplant. But, the recovery is quicker because the transplant tissue is thinner.
o Your eye surgeon will choose the type of surgery based on your cornea’s condition

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