We see through the cornea, which is the clear, central part of the front surface of the eye. The cornea normally has a round shape, like a ball. Sometimes, however, the structure of the cornea is not strong enough to hold this round shape. Over time, the normal round curvature of the surface of the eye can bulge outward like a cone. This condition is called keratoconus.
Keratoconus usually begins in the teenage years, but it can also start in childhood or up to about age 30. In some cases, keratoconus is diagnosed at a later age, but usually only because it is very mild. The changes in the shape of the cornea occur slowly, usually over several years.
Keratoconus changes vision in two ways:
- As the cornea changes from a ball shape to a cone shape, the smooth surface also becomes slightly wavy. This change is called irregular astigmatism.
- As the front of the cornea expands, the eye becomes more nearsighted (poor vision at distance; only nearby objects can be seen clearly). This may require frequent changes in your eyeglass prescription.
What are the symptoms of keratoconus?
The main symptoms of keratoconus are:
- gradual worsening of vision in one or both eyes, usually in late adolescence;
- double vision when looking with just one eye, even with your glasses on;
- bright lights look like they have halos around them.
Someone with keratoconus will notice that his or her vision slowly becomes distorted. The change can stop at any time, or it can continue for several years. In most people who have keratoconus, both eyes are eventually affected.
Why do people get keratoconus?
Often, the cause of keratoconus is unknown. Some studies have found that keratoconus runs in families, and that it happens more often in people with certain medical conditions. But usually, there is no eye injury or disease that explains why the eye starts to change. Patients with keratoconus tend to rub their eyes frequently, which may speed up the progression of the condition.
Can keratoconus damage vision?
Keratoconus rarely leads to permanent vision loss. However, the changes to the cornea make it impossible for the eye to focus without eyeglasses or contact lenses.
Keratoconus can be dangerous if laser vision correction surgery – LASIK or PRK – is performed on the eye because it can worsen the condition. Anyone with even a small degree of keratoconus should not have laser vision correction surgery, unless recommended by your physician in very specific circumstances.
How is keratoconus diagnosed?
Your doctor must measure the curvature of the cornea in order to make a diagnosis of keratoconus. Several different tests can be performed to make the diagnosis.
The most common of these tests is called topography. Topography measures the curvature of the surface of the eye and creates a colored “map” of the cornea. Keratoconus causes very distinctive changes in the appearance of these maps, which allows your doctor to make the diagnosis. Newer technologies exist which may allow for earlier detection of keratoconus, even before changes on topography. Many refractive laser surgeons will perform these tests before offering laser vision correction.
How is keratoconus treated?
Depending on the severity of keratoconus, treatment options may differ. Early in the course of the disease, vision correction may be obtained with normal eyeglasses or soft contact lenses.
As the condition advances, it may be necessary to be fit with a special type of hard contact lens. At this stage, vision may no longer be correctable with eyeglasses because of the amount of irregular astigmatism caused by keratoconus. For some patients, the disease may progress to a stage at which they cannot have acceptable vision with glasses or contact lenses. At this stage, your physician may recommend a cornea transplant.
Two newer treatments for keratoconus have been developed in the past decade: implantable ring segments (often referred to as Intacs) and cornea crosslinking. Implantable ring segments are small devices that can be permanently inserted into the cornea to improve vision or make it easier to fit a patient with contact lenses. Cornea crosslinking is a special type of ultraviolet light treatment that may slow or stop the progression of keratoconus in patients in the earlier stages of the disease. Not all patients with keratoconus are candidates for these treatments. Your doctor can help to decide which, if any, of these treatments may help you.
Does a patient with keratoconus need surgery?
Many patients with keratoconus will never progress to the stage at which cornea transplantation is needed. Newer treatments like cornea crosslinking may be effective in slowing or stopping the progression of patients with less advanced stages of the disease. In the event that vision is no longer correctable with glasses or contact lenses, surgery may be recommended. Keratoconus patients typically get excellent results with cornea transplantation surgery, although the full recovery may take more than one year before new glasses or contact lenses can be prescribed.
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