We see through the cornea, which is the clear outer lens or "windshield" of the eye. Normally, the cornea has a dome shape, like a ball. Sometimes, however, the structure of the cornea is just not strong enough to hold this round shape and the cornea bulges outward and downward like a cone. This condition is called keratoconus.
What Causes Keratoconus?
Tiny fibers of protein in the eye called collagen help hold the cornea in place and keep it from bulging. When these fibers become weak, they cannot hold the shape and the cornea becomes progressively more cone shaped.
Keratoconus is caused by a decrease in protective antioxidants in the cornea. The cornea cells produce damaging by-products, like exhaust from a car. Normally, antioxidants get rid of them and protect the collagen fibers. If antioxidant levels are low, the collagen weakens and the cornea bulges out.
Keratoconus is genetic, so it can run in families. If you have it and have children, it’s a good idea to have their eyes checked for it starting at age 10. The condition progresses more rapidly in people with certain medical problems, including certain allergic conditions. It could be related to chronic eye rubbing.
Keratoconus usually starts in the teenage years. It can, though, begin in childhood or in people up to about age 30. It's possible it can occur in people 40 and older, but that is less common.
The changes can stop at any time, or they can continue for decades. There is no way to predict how it will progress. In most people who have keratoconus, both eyes are eventually affected, although not always to the same extent. It usually develops in one eye first and then later in the other eye.
With severe keratoconus, the stretched collagen fibers can lead to severe scarring. If the back of the cornea tears, it can swell and take many months for the swelling to go away. This often causes a large corneal scar.
Can Keratoconus Damage Vision?
Laser vision correction surgery -- LASIK - is dangerous for people with keratoconus or a strong family history of keratoconus, because it can further weaken the cornea and make vision worse. Anyone with even a small degree of keratoconus should not have LASIK surgery.
How Is Keratoconus Diagnosed?
Keratoconus changes vision in two ways:
- As the cornea changes from a ball shape to a cone shape, the smooth surface becomes distorted. This is called irregular astigmatism.
- As the front of the cornea expands, vision becomes more nearsighted. That is only up close objects can be seen clearly. Anything too far away will look like a blur.
An eye doctor may notice symptoms during an eye exam. You may also mention symptoms that could be caused by keratoconus. These include:
- A sudden change of vision in one eye
- Double vision when looking with just one eye
- Objects both near and far looking distorted
- Bright lights looking like they have halos around them
- Lights streaking
- Seeing double or triple ghost images
- Being uncomfortable driving due to blurry vision, especially at night
To be sure you have keratoconus, your doctor needs to measure the shape of the cornea. There are several different ways this can be done.
The most common way is called ‘corneal topography,’ which snaps a photo of the cornea and analyzes it in seconds. Children of parents with keratoconus should have a cornea topography done every year starting at age 10 to monitor the cornea. Even if your child's corneal topography is normal, it’s still important to have this test performed yearly. There may be subtle changes over time that indicate the disease has started. With annual tests, your doctor can compare results to identify those changes if they're present.
How Is Keratoconus Treated?
Treatment usually starts with new eyeglasses. If eyeglasses don't provide adequate vision, then contact lenses, usually rigid gas permeable or scleral contact lenses, may be recommended. With mild cases, new eyeglasses can usually make vision clear again. Eventually, though, it will probably be necessary to use contact lenses or seek other treatments to strengthen the cornea and improve vision.
A treatment called cornea collagen crosslinking is often effective to help prevent worsening. Intacs are implants that are placed under the surface of the cornea to reduce the cone shape and improve vision.
A specialized laser procedure called PTK can smooth out a raised scar (like a callus) and improve contact lens comfort.
If eyeglasses and contact lenses no longer provide stable and comfortable good quality vision, a cornea transplant can be performed. This involves removing the center of the cornea and replacing it with a donor cornea that is stitched into place. This is typically only done as a last resort.