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Your cornea is the rounded front part of your eye. Keratoconus (also known as KC, bulging cornea, or conical cornea) is a progressive eye disease in which your cornea thins, causing it to bulge into a cone-like shape.
A cone-shaped cornea deflects light as it enters your eye on the way to the retina (the light-sensitive part of your eye). This can cause blurred vision and sensitivity to light and glare.
Often, keratoconus will initially develop in only one eye. But in most cases, both eyes will eventually be affected, possibly to different extents. Because it is a progressive vision disorder, it usually gets worse with age. The adverse changes to the shape of the cornea can stop at any time, or continue throughout your lifetime.
Keratoconus affects roughly 1 in 2,000 people. It is most common in people aged 10-25. For many patients, it begins in their late teens and progresses until their mid-thirties.
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What causes Keratoconus?
There is no known cause of keratoconus. Researchers have studied both genetic and environmental factors that may lead to the development of this eye condition. However, the research so far has been inconclusive.
Some doctors believe that genetics and family history may play a role in the development of a bulging cornea. Over a dozen genes have been associated with keratoconus, though the hereditary pattern is not significant or predictable.
Excessive or vigorous eye rubbing is also commonly associated with keratoconus. However, it is unknown whether eye rubbing causes the disorder, or if it is a reaction to the discomfort experienced in the early stages. Either way, it likely worsens the condition.
Approximately 30 percent of people with keratoconus have some type of allergic disorder. This is not fully understood either. Allergies may trigger eye rubbing, leading to the thinning of the cornea.
Keratoconus Signs and Symptoms
Early signs of keratoconus include:
- Sudden vision change in one eye
- Double vision when looking with one eye
- Slightly distorted vision (straight lines appearing bent or wavy)
- Bright light sensitivity
- Glare sensitivity
- Haloed or streaky vision around lights
- Clouded vision
- Poor night vision
- Red or swollen eyes
As your cornea thins and bulges, the shape of your eye changes. This is known as irregular astigmatism and causes nearsightedness (myopia). Objects up close are visible, but anything further away is blurry.
When to See a Doctor
If you experience any of the signs above or are having difficulty driving, especially at night, you should see an eye doctor. They will perform an eye exam to determine whether you have keratoconus or not.
How Keratoconus is Diagnosed
To be sure that you have keratoconus, an optometrist will measure the shape of your cornea. This can be done in several ways.
Keratometry is a procedure that measures the anterior curvature of your cornea. The optometrist uses a keratometer to shine a circle of light on your eye. He then measures its reflection to determine the shape of your cornea.
The most accurate and common method is corneal topography. This is a simple, non-invasive procedure. The patient sits in front of a machine and looks into a lens. A computer then records images of your cornea to make a detailed map of your cornea that shows its shape and thickness.
In a slit-lamp examination, your eye doctor will shine a vertical beam of light on your eye and use a low-power microscope to examine the cornea's shape. They can also look for additional problems with your eye.
Keratoconus Treatment Options
The best treatment depends on the severity of your condition as well as how quickly the disease is progressing. In the early stages, keratoconus usually has mild or moderate effects on your vision. If this is the case, normal soft contact lenses or eyeglasses can be used for vision correction.
However, as the disease progresses, you will have to change your prescription frequently to make sure you have correct vision. If your case of keratoconus is progressing further or more rapidly, you may need more specialized treatment.
Specialty Contact Lenses
If soft contact lenses are not able to fully correct your vision, most eye doctors will recommend using a different type of lens to correct your vision. These may include:
- Hard contact lenses. Hard, also known as rigid gas permeable contact lenses, may be used if soft contact lenses do not provide full visual acuity. They cover your cornea and replace the cone shape with a smooth uniform surface to refract light properly.
- Piggyback lenses. If hard contact lenses are uncomfortable, some optometrists may prescribe a soft contact lens with a hard lens placed over it. This is known as “piggybacking lenses.”
- Hybrid lenses. Hybrid lenses have a soft outer section, combined with a hard, gas permeable center section that vaults over the eye.
- Scleral lenses. These are larger versions of hard lenses. Rather than resting on the cornea, the scleral lens rests on the white part of your eye.
- Custom soft lenses. A relatively new option, custom soft lenses are created on a made-to-order basis based on detailed measurements of a keratoconus patient. These are much more costly than traditional soft lenses, but may be covered by vision insurance.
Corneal Collagen Cross-Linking
Also known as Corneal cross-linking, or CXL, this procedure stops the bulging of your cornea by strengthening the corneal tissue. This can be done invasively by removing the epithelium (outer layer of the cornea), or non-invasively by keeping the epithelium on. The surgeon saturates the cornea with eye drops containing riboflavin and treats them with ultraviolet (UV) light.
If done early enough, corneal collagen cross-linking may halt the progression of keratoconus and stabilize vision. This will reduce the need for corneal transplants later in life.
Corneal Inserts (Intacs)
Intacs are small, arc-shaped, clear plastic inserts. During the surgery, an ophthalmologist will position the Intacs within the peripheral cornea to reshape and stabilize the front surface of the eye.
Intacs are often used if a patient’s vision has progressed to a point where glasses or normal contact lenses cannot correct their vision. The inserts can be removed and replaced. However, if your keratoconus continues progressing, Intacs may only delay the progression. They cannot prevent a corneal transplant.
Surgeons may combine corneal cross-linking and Intacs, which may prove to be more effective than treating keratoconus with either procedure alone.
Cornea Transplant Surgery
If you have extreme corneal thinning or scarring, you may need a corneal transplant (known as keratoplasty). This is the final treatment option for keratoconus patients. Doctors will remove a portion of your cornea and replace it with a donor cornea.
