What is keratoconus?
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 is detected in the teenage years or 20’s, but it can also start in childhood. In some cases, keratoconus is diagnosed at a later age, but usually only when it is mild. The changes in the shape of the cornea occur over several years, but at a more rapid rate in younger patients.
Keratoconus changes vision in two ways:
- As the cornea changes from a ball shape to a cone shape, the smooth surface also warps. This change is called irregular astigmatism, which cannot be fully corrected with glasses.
- As the front of the cornea steepens, the eye becomes more nearsighted (poor vision at distance; only nearby objects can be seen clearly). As a result, the person may need new eyeglasses more often.
Symptoms and Causes
What are the symptoms of keratoconus?
The main symptoms of keratoconus are the following:
- The vision in one or both eyes gradually gets worse, usually in late adolescence.
- The person may have double vision when looking with just one eye, even with 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 end 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?
The cause of keratoconus is largely unknown. Some studies have found that keratoconus runs in families, and that it happens more often in people who have certain medical conditions. But in most cases, there is no eye injury or disease that explains why the eye starts to change. Patients with keratoconus tend to rub their eyes a lot, which may cause the condition to develop more rapidly.
Diagnosis and Tests
How is keratoconus diagnosed?
In order to make a diagnosis of keratoconus, the doctor must measure the curvature of the cornea. Several different tests can be performed to make the diagnosis. The test that is used most often 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 the doctor to make the diagnosis.
There are newer technologies that may allow keratoconus to be found earlier, even before changes on topography. Refractive laser surgeons will often perform these tests before offering laser vision surgery since patients with signs of keratoconus are not candidates for LASIK and most other forms of laser vision correction.
Management and Treatment
Can keratoconus damage vision?
Untreated keratoconus can lead to permanent vision loss. The changes to the cornea make it difficult for the eye to focus with or without eyeglasses or standard soft contact lenses.
Keratoconus can be dangerous if laser vision correction surgery such as LASIK is performed on the eye, because it can make the condition worse. Anyone who has even a small degree of keratoconus should not have laser vision correction surgery, unless recommended by the doctor in very specific circumstances.
How is keratoconus treated?
There are several methods for treating keratoconus, depending on how severe the condition is. In the early stages of the disease, vision can be corrected with normal eyeglasses or soft contact lenses.
As keratoconus gets worse, vision may no longer be correctable with eyeglasses because of the amount of irregular astigmatism, and so the patient may need to be fit with a special type of hard contact lens.
For some patients, the disease may advance to a stage at which they do not have acceptable vision even with glasses or contact lenses. At this point, the doctor may recommend a cornea transplant, which is a surgical procedure to replace the cornea with a cornea from a donor.
Two additional treatments for keratoconus are implantable ring segments (often referred to as INTACS) and corneal crosslinking:
- Implantable ring segments are small devices that are inserted into the cornea to improve vision or make it easier to fit a patient with contact lenses. In this procedure, which is performed under local anesthesia (the patient’s eye is numbed with drops), the doctor creates channels in the cornea and inserts the rings into these channels. The rings help to flatten the cornea and partially correct the cone shape caused by the keratoconus.
- Corneal crosslinking uses ultraviolet light treatment that may slow or stop the keratoconus from getting worse. In this procedure, the patient also receives local anesthesia. Drops of a drug containing riboflavin (vitamin B2) are put into the eye for up to 30 minutes. The eye is then exposed to an ultraviolet light for up to 30 minutes. The corneal crosslinking procedure is designed to strengthen the bonds between the cornea’s collagen fibers and surrounding proteins, which can help keep the cornea from steepening.
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 need a cornea transplant. Corneal crosslinking is a major advance in slowing or stopping keratoconus, and treatment is important to consider especially in young patients with evidence of keratoconus so that loss of vision can be minimized.
In cases in which vision can no longer be corrected with glasses or contact lenses, surgery may be recommended. Keratoconus patients usually experience improved vision with cornea transplantation surgery, although it may take more than a year for vision to stabilize and for a patient to benefit from new glasses or contact lenses. Some patients still require a specialty contact lens after their corneal transplant to get their best vision.