Keratoconus (ker-uh-toe-KOH-nus) occurs when your cornea — the clear, dome-shaped front surface of your eye — thins and gradually bulges outward into a cone shape.

A cone-shaped cornea causes blurred vision and may cause sensitivity to light and glare. Keratoconus usually affects both eyes, though it often affects one eye more than the other. It generally begins to affect people between the ages of 10 and 25. The condition may progress slowly for 10 years or longer.

In the early stages of keratoconus, you might be able to correct vision problems with glasses or soft contact lenses. Later, you may have to be fitted with rigid, gas permeable contact lenses or other types of lenses, such as scleral lenses. If your condition progresses to an advanced stage, you may need a cornea transplant.

A new treatment called corneal collagen cross-linking may help to slow or stop keratoconus from progressing, possibly preventing the need for a future cornea transplant. This treatment may be offered in addition to the vision correction options above.

Signs and symptoms of keratoconus may change as the disease progresses. They include:

• Blurred or distorted vision
• Increased sensitivity to bright light and glare, which can cause problems with night driving
• A need for frequent changes in eyeglass prescriptions
• Sudden worsening or clouding of vision

When to see a doctor

See your eye doctor (ophthalmologist or optometrist) if your eyesight is worsening rapidly, which might be caused by an irregular curvature of the eye (astigmatism). He or she may also look for signs of keratoconus during routine eye exams.

No one knows what causes keratoconus, although genetic and environmental factors are thought to be involved. Around 1 in 10 people with keratoconus also have a parent with the condition.

These factors can increase your chances of developing keratoconus:

• Having a family history of keratoconus
• Rubbing your eyes vigorously
• Having certain conditions, such as retinitis pigmentosa, Down syndrome, Ehlers-Danlos syndrome, hay fever and asthma

In some situations, your cornea may swell quickly and cause sudden reduced vision and scarring of the cornea. This is caused by a condition in which the inside lining of your cornea breaks down, allowing fluid to enter the cornea (hydrops). The swelling usually subsides by itself, but a scar may form that affects your vision.

Advanced keratoconus also may cause your cornea to become scarred, particularly where the cone is most prominent. A scarred cornea causes worsening vision problems and may require cornea transplant surgery.

To diagnose keratoconus, your eye doctor (ophthalmologist or optometrist) will review your medical and family history and conduct an eye exam. He or she may conduct other tests to determine more details regarding the shape of your cornea. Tests to diagnose keratoconus include:

• Eye refraction. In this test your eye doctor uses special equipment that measures your eyes to check for vision problems. He or she may ask you to look through a device that contains wheels of different lenses (phoropter) to help judge which combination gives you the sharpest vision. Some doctors may use a hand-held instrument (retinoscope) to evaluate your eyes.
• Slit-lamp examination. In this test your doctor directs a vertical beam of light on the surface of your eye and uses a low-powered microscope to view your eye. He or she evaluates the shape of your cornea and looks for other potential problems in your eye.
• Keratometry. In this test your eye doctor focuses a circle of light on your cornea and measures the reflection to determine the basic shape of your cornea.
• Computerized corneal mapping. Special photographic tests, such as corneal tomography and corneal topography, record images to create a detailed shape map of your cornea. Corneal tomography can also measure the thickness of your cornea. Corneal tomography can often detect early signs of keratoconus before the disease is visible by slit-lamp examination.

Treatment for keratoconus depends on the severity of your condition and how quickly the condition is progressing. Generally, there are two approaches to treating keratoconus: slowing the progression of the disease and improving your vision.

If your keratoconus is progressing, corneal collagen cross-linking might be indicated to slow or stop the progression. This is a newer treatment that has the potential to prevent you from needing a cornea transplant in the future. However, this treatment does not reverse keratoconus or improve vision.

Improving your vision depends on the severity of keratoconus. Mild to moderate keratoconus can be treated with eyeglasses or contact lenses. This will likely be a long-term treatment, especially if your cornea becomes stable with time or from cross-linking.

In some people with keratoconus, the cornea becomes scarred with advanced disease or wearing contact lenses becomes difficult. In these people, cornea transplant surgery might be necessary.

Lenses

• Eyeglasses or soft contact lenses. Glasses or soft contact lenses can correct blurry or distorted vision in early keratoconus. But people frequently need to change their prescription for eyeglasses or contacts as the shape of their corneas change.
• Hard contact lenses. Hard (rigid, gas permeable) contact lenses are often the next step in treating more-advanced keratoconus. Hard lenses may feel uncomfortable at first, but many people adjust to wearing them and they can provide excellent vision. This type of lens can be made to fit your corneas.
• Piggyback lenses. If rigid lenses are uncomfortable, your doctor may recommend "piggybacking" a hard contact lens on top of a soft one.
• Hybrid lenses. These contact lenses have a rigid center with a softer ring around the outside for increased comfort. People who can't tolerate hard contact lenses may prefer hybrid lenses.
• Scleral lenses. These lenses are useful for very irregular shape changes in your cornea in advanced keratoconus. Instead of resting on the cornea like traditional contact lenses do, scleral lenses sit on the white part of the eye (sclera) and vault over the cornea without touching it.

If you're using rigid or scleral contact lenses, make sure to have them fitted by an eye doctor with experience in treating keratoconus. You'll also need to have regular checkups to determine whether the fitting remains satisfactory. An ill-fitting lens can damage your cornea.

Therapies

• Corneal collagen cross-linking. In this procedure, the cornea is saturated with riboflavin eyedrops and treated with ultraviolet light. This causes cross-linking of the cornea, which stiffens the cornea to prevent further shape changes. Corneal collagen cross-linking may help to reduce the risk of progressive vision loss by stabilizing the cornea early in the disease.

Surgery

You may need surgery if you have corneal scarring, extreme thinning of your cornea, poor vision with the strongest prescription lenses or an inability to wear any type of contact lenses. Depending on the location of the bulging cone and the severity of your condition, surgical options include:

• Penetrating keratoplasty. If you have corneal scarring or extreme thinning, you'll likely need a cornea transplant (keratoplasty). Penetrating keratoplasty is a full-cornea transplant. In this procedure, doctors remove a full-thickness portion of your central cornea and replace it with donor tissue.
• Deep anterior lamellar keratoplasty (DALK). The DALK procedure preserves the inside lining of the cornea (endothelium). This helps avoid the rejection of this critical inside lining that can occur with a full-thickness transplant.

Cornea transplant for keratoconus generally is very successful, but possible complications include graft rejection, poor vision, infection and astigmatism. Astigmatism is often managed by wearing hard contact lenses again, which is usually more comfortable after a cornea transplant.

If you're having difficulty with your vision, you'll likely start by seeing an eye doctor (ophthalmologist or optometrist). If your eye doctor determines that you might have keratoconus, you may be referred to an ophthalmologist who has had special training in corneal disease and surgery to get and interpret corneal imaging studies and to determine if you need cross-linking or a cornea transplant.

Here's some information to help you get ready for your appointment.

What you can do

Before your appointment make a list of:

• Symptoms you've been having and for how long
• Recent major stresses or life changes
• All medications, eyedrops, vitamins and supplements you take, including the doses
• Questions to ask your doctor

For keratoconus some basic questions to ask your doctor include:

• What's the most likely cause of my symptoms?
• What are other possible causes?
• Do I need any tests?
• Is this condition temporary?
• What treatments are available, and which do you recommend?
• What are the alternatives to the primary approach you're suggesting?
• I have other health conditions. How can I best manage them together?
• Do you have any brochures or other printed material I can take with me? What websites do you recommend?

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

• What types of signs and symptoms have you been having?
• When did you begin experiencing symptoms?
• Have your symptoms been continuous or occasional?
• How severe are your symptoms?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Does anyone in your family have keratoconus?