Corneal Ectasia

What Is Corneal Ectasia?

Corneal ectasia is an abnormal thinning of the cornea. The cornea is a transparent tissue covering the front of your eye and helps to focus light entering your eye.

A healthy cornea is essential to maintain clear vision. Although rare, corneal ectasia is a sight-threatening condition that can cause permanent damage to the eye.

What Causes Corneal Ectasia?

There are several causes of corneal ectasia, including:

• Keratoconus is a corneal disease that causes gradual thinning and steepening of the cornea. The steepening causes the cornea to develop a cone shape, which is where the term keratoconus comes from. Studies show there may be a genetic component involved. Keratoconus often causes irregular astigmatism and decreased vision. 
• Pellucid marginal degeneration is a corneal disease that causes thinning in the lower, peripheral area of your cornea. This condition also causes irregular astigmatism and decreased vision.
• Keratoglobus is a rare eye disease that causes thinning of the cornea, particularly in the peripheral areas. Keratoglobus may be associated with connective tissue diseases (diseases affecting the skin, joints, and blood vessels) such as Ehlers-Danlos Syndrome.
• Laser eye surgery, such as laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and photorefractive keratectomy (PRK) can also induce corneal ectasia. 

Post-LASIK Ectasia

Post-surgical corneal ectasia is a rare complication of LASIK, but it can cause severe vision problems. Before LASIK surgery, your eye surgeon performs a variety of tests to assess if you are a suitable candidate for the procedure. 

Possible Risk Factors

These are some factors that influence your risk for post-surgical corneal ectasia, including:

• Corneal thickness. This measurement tells the surgeon how much corneal tissue you have. During LASIK, the laser reshapes your cornea, which thins out the tissue. If your corneas are already thin, you may not be a suitable candidate for LASIK.
• High myopia. The amount of corneal tissue removed during LASIK surgery depends on how high your prescription is. If you have high myopia (nearsightedness), the surgeon may feel it’s too risky to perform LASIK, since it could leave you with thin corneas.
• Corneal topography. This measurement provides a map of the front of your cornea. The surgeon can see which areas of your cornea are flatter or steeper, just like viewing mountains and valleys on a geographical map. If you have any irregularities or steepening of your cornea, you may be showing early signs of keratoconus and ineligible for LASIK.

If the surgeon determines you are at a higher risk for corneal ectasia after LASIK surgery, they may recommend an alternative procedure or no surgery altogether. 

Corneal Ectasia Symptoms

After LASIK treatment, your eye surgeon will follow up with you over several visits to ensure your eyes are healing properly. These are some potential signs and symptoms of post-LASIK corneal ectasia: 

• Blurry vision or fluctuating vision. If you notice your vision is getting worse after LASIK, your eye doctor should examine your eyesight to see if you need a prescription. If they cannot correct your vision with an eyeglass prescription, this could be a sign that you are developing corneal ectasia.
• Seeing glare, haloes, or starbursts around lights. It’s normal to see some of these light-related distortions post-LASIK. However, if your symptoms are getting worse, your eye doctor should examine you for signs of corneal ectasia.
• Increasing myopia or astigmatism. These changes can be signs of regression, which is when the effects of LASIK start to wear off. However, corneal ectasia can also cause myopia or astigmatism, especially irregular astigmatism. 
• Corneal steepening. This finding can indicate corneal ectasia. If the steepening is severe enough, your cornea develops an irregular, bulged-out appearance.

How to Diagnose Corneal Ectasia

The following tests can help determine if you have corneal ectasia:

• Corneal topography. Your eye surgeon may perform a corneal topography measurement to see if you show signs of corneal steepening, which can cause irregular astigmatism. 
• Corneal tomography. This test can provide even more information than a corneal topography by imaging both the front and back surfaces of the cornea. The instrument generates a 3D model of your cornea and also gives the doctor information on the corneal thickness.

Corneal Ectasia Treatment

If your doctor determines you have corneal ectasia, there are several treatment options available. They may also recommend that you avoid rubbing your eyes as much as possible. 

Studies show that excessive eye rubbing can contribute to corneal ectasia. 

Treatments range from conservative to invasive, and may include:

Glasses

For mild cases of corneal ectasia that are not progressive, glasses may provide some vision correction. However, most patients still notice blurry or distorted vision with glasses, especially if they have irregular astigmatism.

Specialty contact lenses

These contact lenses offer better visual quality than soft contacts since they can compensate for irregular astigmatism. They include rigid gas permeable lenses, scleral lenses, and hybrid lenses (combination lenses with a rigid portion in the center and a soft skirt on the edges). 

Collagen cross-linking (CXL)

This procedure treats post-surgical corneal ectasia, along with keratoconus and pellucid marginal degeneration. Collagen cross-linking works by strengthening and stabilizing the cornea to slow down corneal thinning. 

• First, the surgeon may remove the upper layer of your cornea, which is called an epithelium-off procedure. A less invasive corneal cross-linking procedure is epithelium-on, where the surgeon does not remove the top layer of the cornea. 
• Then, the surgeon applies a riboflavin (vitamin B₂ ) solution on the eye and uses ultraviolet light to activate the riboflavin.

Intracorneal ring segments

These are small, crescent-shaped implants that are placed into the cornea to flatten out an abnormally steep cornea. This is an effective way to improve irregular astigmatism. Some surgeons combine this procedure with collagen cross-linking, as some studies show added benefits.

Corneal transplants

This type of surgery, also called keratoplasty, includes penetrating (full-thickness) or lamellar (partial-thickness). A penetrating keratoplasty replaces the entire cornea. Lamellar keratoplasties replace the front and middle layers of the cornea. 

Most surgeons prefer lamellar keratoplasties for treating corneal ectasia if the back layer of the cornea is healthy. These procedures are more invasive than other treatments. Surgeons typically reserve corneal transplants for when other treatments fail, or if the ectasia is severe.