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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 begins to first affect people ages 10 to 25. The condition may progress slowly for 10 years or longer.
In the early stages of keratoconus, you can 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. If your condition progresses to an advanced stage, you may need a cornea transplant.
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).
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.
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 optical coherence tomography and corneal topography, record images of your cornea to create a detailed shape map of your cornea's surface. The tests can also measure the thickness of your cornea.
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 many people, the cornea will become stable after a few years. If you have this type, you likely won't experience severe vision problems or require further treatment.
In some people with keratoconus, the cornea becomes scarred or wearing contact lenses becomes difficult. In these cases, surgery might be necessary.
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 progressing 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.
Corneal cross-linking. In this procedure, the cornea is saturated with riboflavin drops and treated with ultraviolet light. Corneal cross-linking may help to reduce the risk of progressive vision loss by stabilizing the cornea early in the disease.
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. Several surgeries are available, depending on the location of the bulging cone and the severity of your condition.
Surgical options include:
Corneal inserts. During this surgery, your doctor places tiny, clear, crescent-shaped plastic inserts (intracorneal ring segments) 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 a cornea transplant. This surgery may also make it easier to fit and tolerate contact lenses. The corneal inserts can be removed, so the procedure can be considered a temporary measure.
Cornea transplant. 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.
A deep anterior lamellar keratoplasty (DALK) preserves the inside lining of the cornea (endothelium). It 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, astigmatism, inability to wear contact lenses and infection.
Preparing for an appointment
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 may need a cornea transplant, you may be referred to an ophthalmologist who has had special training in corneal surgery.
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?