Mayo Clinic Health Library

Keratoconus

Updated: 02-20-2013

Definition

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 and generally occurs in people ages 10 to 25. The condition may progress slowly for 10 years or longer.

Vision problems can be corrected with glasses or soft contact lenses early on in the condition. As keratoconus progresses, you may have to be fitted with rigid gas permeable contact lenses or other types of contact lenses. Advanced keratoconus may require a cornea transplant.

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Symptoms

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

  • Blurred or distorted vision
  • Increased sensitivity to bright light and glare
  • Problems with night vision
  • Many changes in eyeglass prescriptions
  • Sudden worsening or clouding of vision, caused by a condition in which the back of your cornea ruptures and fills with fluid (hydrops)

When to see a doctor
See your eye doctor (ophthalmologist or optometrist) if you have irregular curvature of the eye (astigmatism) and your eyesight is worsening rapidly. Your eye doctor also may look for signs of keratoconus during routine eye exams.

If you're considering laser-assisted in-situ keratomileusis (LASIK) eye surgery, make sure your doctor checks for signs of keratoconus before you proceed.

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Causes

The cause of keratoconus is unknown.

Keratoconus may be associated with:

  • Vigorous rubbing of your eyes
  • Other eye conditions, including retinitis pigmentosa, retinopathy of prematurity or vernal keratoconjunctivitis
  • A combination of several disorders, such as enzyme abnormalities or hereditary factors including Down syndrome
  • Wearing contact lenses for several years
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Risk factors

These factors can increase your chances of developing keratoconus:

  • Certain diseases. The risk of developing keratoconus may be higher if you have certain inherited diseases or genetic conditions, such as Down syndrome, Leber's congenital amaurosis, Ehlers-Danlos syndrome or osteogenesis imperfecta.
  • Family history of keratoconus. If you have a family history of keratoconus, you may have a higher chance of developing keratoconus.
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Complications

In some situations, your cornea may swell quickly and cause sudden reduced vision and scarring of the cornea.

In advanced keratoconus, your cornea may become scarred, particularly where the cone forms. A scarred cornea causes worsening vision problems and may require corneal transplant surgery.

The effect of ongoing vision problems on your daily life also can lead to anxiety. However, finding ways to adapt to your condition can lessen anxiety.

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Preparing for your appointment

If you're having difficulty with your vision, you'll likely start by seeing an eye doctor (ophthalmologist). If your eye doctor determines that you may need a cornea transplant, you may be referred to an ophthalmologist who has had special training in corneal surgery.

Because appointments can be brief and there's often a lot to talk about, it's a good idea to be prepared. Here's some information to help you get ready, and what to expect from your eye doctor.

What you can do

  • Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment. Also, write down key personal information, including any major stresses or recent life changes.
  • Make a list of all medications, including eyedrops, vitamins and supplements that you're using or taking.
  • Ask a family member or friend to come with you. Someone who accompanies you may remember something that you missed or forgot.
  • Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions will help you make the most of your time together. List your questions from most important to least important in case time runs out. For keratoconus, some basic questions to ask your doctor include:

  • What do you think is causing my symptoms?
  • Are there any other possible causes for my symptoms?
  • Do I need any special tests?
  • Is this condition temporary?
  • What treatments are available? Which do you recommend?
  • Are there alternatives to the primary approach that you're suggesting?
  • I have another health condition. How can I best manage these conditions together?
  • Are there any brochures or other printed material that I can take with me? What websites do you recommend?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over points you want to spend more time on. Your doctor may ask:

  • 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?
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Tests and diagnosis

To diagnose keratoconus, your eye doctor (ophthalmologist) will review your symptoms and medical history and conduct a routine eye examination. Your eye doctor may conduct other tests to determine the exact shape of your cornea. Tests to diagnose keratoconus include:

  • Eye refraction. In this standard vision test, your eye doctor uses special equipment that measures your eyes to check for astigmatism and other vision problems.

    Your eye doctor may ask you to look through a device that contains wheels of different lenses, to help determine which combination of lenses give you the sharpest vision. Doctors may use a hand-held instrument (retinoscope) to evaluate your eye's projection and reflection of light.

    This test may include a measurement taken by a special instrument (automatic refractor), which automatically checks how light is projected and reflected by your eye.

  • 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. Your doctor will evaluate the shape of your cornea and look for other potential problems in your cornea or other parts of your eye.

    The test may be repeated after eyedrops are used to dilate your pupils so that the doctor can view the back of your cornea.

  • Keratometry. In this test, your eye doctor focuses a circle of light on your cornea. Your doctor measures the reflection to evaluate the curve of your cornea.
  • Computerized corneal mapping. Optical scanning techniques, such as optical coherence tomography and corneal topography, take images of your cornea. The tests create a topographical map of your cornea's surface and measure the thickness of your cornea.
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Treatments and drugs

Treatment for keratoconus depends on the severity of your condition and how quickly the condition is progressing.

Mild to moderate keratoconus can be treated with eyeglasses or contact lenses. For most people, the cornea will become stable after a few years. You often won't experience severe vision problems and require further treatment.

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

Lenses
For most people with keratoconus, contact lenses are the most effective treatment.

  • 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.
  • Rigid gas permeable contact lenses. Hard (rigid gas permeable) contact lenses are often the next step in treating progressing keratoconus. Rigid lenses may feel uncomfortable at first, but many people adjust to wearing them. Rigid gas permeable lenses 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. Fitting a combination of lenses takes a lot of precision, so be sure you work with a doctor experienced with this technique.
  • 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 contact lenses. These lenses are useful for irregular changes in your cornea and advanced keratoconus. Instead of resting on the cornea like traditional lenses do, scleral contacts sit on the white part of the eye (sclera) and go 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 and refittings because a poor-fitting hard contact lens can damage your cornea.

Surgery
You may need surgery if you have corneal scarring, extreme thinning of your cornea, poor vision with the strongest prescription lenses, or if you can't wear any type of contact lenses. Several surgeries are available, depending on the location of the bulging cone and the severity of your condition. Surgical options include:

  • Corneal inserts (intracorneal ring segments). During this surgery, your doctor inserts two tiny, clear, crescent-shaped plastic inserts into your cornea to flatten the cone, support the cornea's shape and improve vision.

    Corneal inserts can restore a more normal corneal shape, slow progress of keratoconus and reduce the need for cornea transplant. The surgery also makes it easier to fit and tolerate contact lenses. The corneal inserts can be removed, so the procedure can be considered a temporary measure.

    However, the surgery carries risks, such as infection and injury to areas of the eye during surgery.

  • Cornea transplant (keratoplasty). If you have corneal scarring or extreme thinning, you'll likely need a cornea transplant (keratoplasty).

    Lamellar keratoplasty is a partial-thickness transplant, in which only a section of the cornea's surface is replaced.

    Penetrating keratoplasty, the most common cornea transplant, is a full-cornea transplant. In this procedure, doctors remove an entire portion of your cornea and replace it with donor tissue.

    A deep anterior lamellar keratoplasty (DALK) preserves the inner layer of the cornea (endothelium). It helps avoid rejection caused by the endothelial cells in a full-thickness transplant.

    Recovery after keratoplasty can take up to one year, and you may need to continue to wear rigid contact lenses to have clear vision. Full improvement of vision may occur several years after your transplant.

    Cornea transplant generally is very successful, but possible complications include graft rejection, poor vision, astigmatism, inability to wear contact lenses and infection.

Emerging treatment
A new treatment called collagen cross-linking shows promise for people with keratoconus.

After having riboflavin drops applied to your cornea, you're exposed to ultraviolet A (UVA) light. The procedure strengthens the cornea to prevent further thinning or bulging. The treatment is still in the testing phase in the United States, and additional study is needed before it becomes widely available.

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