What Is Corneal Ectasia?
Corneal ectasia is the thinning of the cornea. The cornea is a curved layer of transparent tissue in the eye. It protects the iris and pupil and allows light to enter.
The cornea controls the entry of light and focuses it on the retina. This makes it possible to see things clearly.
Types of Corneal Ectasia
The types of corneal ectatic disorders are:
- Keratoconus. A progressive eye disease that involves gradual thinning of the central cornea. The weak cornea causes the eye to bulge in the shape of a cone.
- Posterior keratoconus. A rare but non-progressive condition. It causes thinning at the inner surface (posterior) of the cornea. Unlike keratoconus, it does not lead to a cone-shaped bulging of the eye.
- Keratoglobus. A rare and degenerative eye disorder with general thinning of the cornea. It is characterized by the round-shaped (globular) bulging of the eyes.
- Pellucid marginal degeneration (PMD). A degenerative form of corneal ectasia. It causes thinning on the lower (inferior) and sides (peripheral) of the cornea.
- Terrien marginal degeneration (TMD). A slowly progressive eye disease that causes peripheral thinning of the cornea.
- Post keratorefractive ectasia. A post-surgical corneal ectasia that occurs as a complication of LASIK or PRK.
- Wound ectasia after penetrating keratoplasty (PK). A corneal ectatic disorder that develops as a complication of corneal transplant.
Laser in-situ keratomileusis (LASIK) is a procedure that corrects vision problems. It is the most popular and most commonly performed corneal refractive surgery.
Post-LASIK ectasia is a rare complication that affects 0.02% to 0.6% of people who undergo LASIK.1
It can cause progressive myopia and astigmatism, leading to worsening eyesight.
Before the procedure, your doctor will assess you to see if you are a suitable candidate. The ophthalmologist will also discuss the benefits and risks of LASIK surgery.
Post-LASIK Ectasia Causes
LASIK uses a special laser to cut and shape the cornea. If too much corneal tissue is removed or becomes damaged, it can cause ectasia.
People with pre-existing corneal problems may also develop post-surgical corneal ectasia.2
Possible Risk Factors
Factors that increase your risk for post-LASIK ectasia are:1,2
- Thin residual stromal bed that is less than 250 um
- Thin corneas that are less than 500 um
- Severe myopia or nearsightedness
- Abnormal corneal topography (e.g., uneven structures)
- History of multiple eye enhancements
The eye surgeon may recommend alternative treatments if LASIK surgery puts you at higher risk for corneal ectasia.
What Causes Corneal Ectasia?
The eye is comprised of different fluids. Your cornea is one of many structures that keeps them in the right place.
If it becomes too thin, fluid from inside the eyes can enter the cornea. Damage to the cornea may also cause swelling and fluid to build up within its layers.
Most corneal ectasias are present in families. This suggests it is a hereditary condition.3,4
Corneal trauma is another possible cause. External factors such as eye surgery, contact lenses, and frequent and aggressive eye rubbing have been associated with ectasia.3,4,5
Other factors that increase your risk for cornea ectasia are:
- Age and gender. TMD is common in middle-aged men.5
- Congenital diseases. Such as Down's syndrome, albinism, and retinitis pigmentosa.
- Connective tissue disorders. Like Marfan, Rubinstein-Taybi Syndrome, and Ehlos-Danlers Syndrome.
- Allergic conditions. Such as asthma, allergies, eczema, and hay fever.
- Inflammatory diseases. Like idiopathic orbital inflammation and thyroid eye disease.
- Medications. Systemic or topical corticosteroid use.6
Corneal Ectasia Symptoms
The symptoms of corneal ectasia can vary for each person. It usually depends on the damage sustained by the cornea.
Common cornea ectasia symptoms include:
- Astigmatism or blurred vision at all distances
- Myopia or nearsightedness (e.g., blurring of distant objects)
- Changes in the shape of the cornea (e.g., coned or globular)
- Seeing glare, halos, and starbursts around lights
- Diplopia or double vision and ghosting
- Corneal hydrops (e.g., watery eyes and light sensitivity)
- Failed attempts to correct vision problems with glasses or contacts
Age can help you determine when these symptoms will appear.
For instance, keratoglobus is prevalent in early life. Keratoconus usually affects people in their 20's and 30's. Meanwhile, PMD is more common for those in their 30's to 50's.
People with PMD and TMD ectasia may be asymptomatic and not develop most of these symptoms.7,8
However, a person with corneal ectasia will generally experience worsening vision. Unless treated, it can lead to vision loss.
What are the Symptoms of Post-LASIK Ectasia?
Some visual disturbances and eye discomfort are normal after LASIK surgery. But if the symptoms persist for several weeks, you may have a post-LASIK corneal ectasia.
Post-LASIK ectasia has the same signs and symptoms as other types of corneal ectasia.
However, these symptoms may not show until after a few months or years since you had LASIK surgery.6
How to Diagnose Corneal Ectasia
An eye specialist will conduct tests to check for signs and symptoms of corneal ectasia.
To find out your risk for corneal ectasia, your doctor may ask questions about:
- Onset and course. When the symptoms appeared and if they worsened.
- History of visual impairment. If you had pre-existing eyesight problems.
- Ocular history. If you had been diagnosed with corneal abnormalities and received treatments such as contact lenses and keratorefractive surgery.
- Medical history. If you have previous or current diseases that puts you at higher risk for corneal ectasia.
- Family history. Presence of corneal ectasia in the family, especially keratoconus.
A doctor will examine you for the following:
- Signs of corneal ectasia and risk factors. Such as protruding corneas, thick and scaly eyelids, floppy eyelids, or swollen inner eyelids.
- Visual function. This includes your visual acuity and whether or not optical devices can correct your vision to 20/20.
- Corneal changes. Such as the presence, location, and severity of corneal thinning, protrusion, and scarring.
- Previous corneal surgery. Like a LASIK flap, lamellar keratoplasty, or a corneal transplant.
- Other possible signs of corneal ectasia. Including lower intraocular pressure (IOP).
These tests can help diagnose corneal ectasia:
The keratometer used to perform this test measures the radius of the corneal curvature. It predicts the focusing power of the cornea.
Keratometry helps doctors check for an irregular corneal surface. It can diagnose irregular astigmatism and corneal steepening.6
The imaging test maps the surface of the cornea. It can help your doctor check for distortions on its curvature.
Corneal topography can diagnose keratoconus, pellucid marginal degeneration, and post-surgical ectasia.6
Optical coherence tomography (OCT)
The non-invasive test takes cross-section images of front part of the eye, including the cornea.
Since these are high-resolution images, a doctor can easily check the size, thickness, and shape of different corneal structures.
OCT can be used in the diagnosis of keratoconus, acute corneal hydrops, corneal edema, and corneal scarring.6
The simple test measures corneal thickness at different points. Doctors may use it to diagnose corneal ectasia.6
Corneal Ectasia Treatment
Once the doctor confirms your diagnosis, you can choose from several treatment options:
Glasses can correct mild cases of non-progressive corneal ectasia. Studies show that eyeglasses can improve your vision by up to 20/20 or 20/40.6
The ophthalmologist may prescribe different lenses, depending on your diagnosis:
- Soft contact lenses. They can improve the vision of people with mild keratoconus.
- Rigid gas-permeable lenses (RGP). Often prescribed as an alternative to eyeglasses that can no longer get your vision up to 20/30.
- Hybrid lenses. They have an RGP center and a soft skirt. Doctors recommend it as an alternative for people with RGP intolerance.
- Piggyback contact lenses. This treatment involves wearing RGP contact lenses on top of soft contacts. It is more comfortable and can prevent corneal damage.
- Scleral lenses. Can be custom-made to fit your eyes. A scleral lens improves visual acuity by clearing the cornea and improving the focus and stability of light.
Corneal cross-linking (CXL)
Corneal collagen cross-linking is a minimally-invasive surgical procedure. It slows down the thinning of the cornea in progressive forms of ectasia.
With that said, it can be used to treat mild to moderate cases of keratoconus and post-surgical corneal ectasia.6
A surgeon may perform epithelium-off, which involves the removal of the outermost layer of the cornea. But they may also decide to keep it with an epithelium-on procedure.
Next, the eye surgeon will apply riboflavin (vitamin B2) solution to the eye. Then they will use a mild ultraviolet light to activate the nutrient.
CXL strengthens and stabilizes the cornea, which helps delay corneal thinning.
Intracorneal ring segment implantation (IRCS)
It is a minimally-invasive procedure that involves the insertion of ring segments into the cornea. These are small, clear, and crescent-shaped implants.
An intracorneal ring can flatten abnormally steep cornea. It treats post-LASIK ectasia and keratoconus.9
Some eye surgeons combine IRCS with CXL to improve outcomes.
Corneal transplantation or keratoplasty is an invasive eye surgery. It is the mainstay treatment for severe corneal ectasia.
Keratoplasty is an option if optical devices like eyeglasses and contact lenses no longer correct your ectasia.
There are two types of corneal transplants:
- Penetrating keratoplasty. The entire cornea is replaced.
- Lamellar keratoplasty. Replaces the front and middle layers of the cornea.
Most surgeons prefer lamellar keratoplasty if the back of the cornea is healthy.
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