Keratoconus occurs when your cornea — the clear, dome-shaped surface of your eye — thins out, gradually producing a cone-shaped bulge in the front of your eye. A cone-shaped cornea causes blurred vision and may cause increased sensitivity to light and glare, as well as headaches from eyestrain. Keratoconus usually affects both eyes and typically begins during puberty or late teens, and then progresses over about 10 years.

In the early stages of keratoconus, the vision problems caused by the distorted cornea can be corrected effectively with glasses or soft contact lenses. As keratoconus progresses, you may have to be fitted with special rigid gas permeable contact lenses. Advanced keratoconus may require surgery.

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

• Blurred or distorted vision
• Increased sensitivity to bright light and glare
• Disturbed night vision
• Headaches from eyestrain
• Hydrops, a condition in which the back of your cornea ruptures and fills with fluid, clouding vision

When to see a doctor
Although your eye doctor will look for signs of keratoconus during routine eye exams, you may want to ask specifically about it if you have astigmatism and your eyesight is worsening rapidly.

A high proportion of people seeking laser-assisted in situ keratomileusis (LASIK) eye surgery have keratoconus and have become frustrated when glasses and contact lenses haven't worked. If you're considering LASIK surgery because your vision is unclear even when you wear glasses or contacts, be sure your doctor checks for signs of keratoconus before you get the surgery.

What triggers corneal thinning in keratoconus is usually unknown. If you have a habit of vigorously rubbing your eyes, however, you might be injuring your corneas, gradually making them thin out and distorting their shape. A few people who habitually rub their eyes develop keratoconus as a result.

Several factors can predispose you to developing keratoconus, including:

• Wearing ill-fitting hard contact lenses. If you wear rigid contact lenses and they haven't been fitted properly, the constant pressure or continual injury they cause can lead to keratoconus.
• Certain inherited diseases. The risk of developing keratoconus is higher if you have certain conditions, such as Down syndrome or certain retinal diseases.
• Family history of keratoconus. Most people with keratoconus have no family history of the disease, but researchers have found that in some cases there may be a family connection.

In advanced keratoconus, your cornea may become scarred, particularly at the point of the cone. A scarred cornea causes additional vision disturbances, and can be corrected only with corneal transplant surgery.

Your ophthalmologist can diagnose keratoconus during a routine eye exam, but more sophisticated tests may be done 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 clear vision, astigmatism and other vision problems. The first measurement is taken by a computerized refractor or by retinoscopy, a light that's reflected by your retina. Then, your eye doctor may ask you to look through a Phoroptor, a mask-like device that contains wheels of different lenses, in order to find the combination that gives you the sharpest vision.
• Slit-lamp examination. This test shines a vertical beam of light on the surface of your eye while the ophthalmologist looks through a low-powered microscope to view the shape of your cornea. The test may be repeated after eyedrops are used to dilate your pupils so that the ophthalmologist can assess the back of your cornea.
• Keratometry. A single circle of light is focused on your cornea, and the reflection of light is used to measure your cornea's curvature and radius.
• Topographical measuring devices. If more precise measurements of your cornea's surface are needed, a computer scans your cornea and generates a topographical map of your eye's surface.

The treatment of keratoconus depends on its severity and rate of progression. Mild or moderate keratoconus can be treated with corrective glasses or contact lenses, but surgery may be necessary for advanced cases or scarring of the cornea.

Lenses

• Glasses or soft contact lenses. Early keratoconus can be treated with glasses or soft contact lenses to correct blurry or distorted vision. But because the condition is progressive, most people find they frequently need to change the prescription of their lenses as their corneas' shape changes.
• Rigid gas permeable contact lenses. Hard contact lenses are often the next step in treating progressing keratoconus. Rigid lenses may feel uncomfortable at first, but many wearers grow accustomed to them.
• Piggyback lenses. If you don't like the feel of rigid lenses, 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 get fitted by a doctor experienced with keratoconus.
• Hybrid lenses. Also for people who can't tolerate hard contact lenses, these contacts have a rigid center with a softer ring around the outside for increased comfort.
• Customized contact lenses. These rigid gas permeable lenses are custom created for each individual based on topographical measurements of your corneas.
• Scleral contact lenses. These lenses are useful for irregular cornea changes, because they rest on the white part of the eye (sclera) and vault over the cornea, instead of resting on the cornea like traditional lenses.

If you're using rigid or scleral contact lenses, be sure that they're fitted by an eye doctor with experience in treating keratoconus, and that you go in for checkups and re-fittings. A poor-fitting hard contact lens can make keratoconus worse.

Surgery
You may need surgery if you have corneal scarring, extreme thinning of your cornea, or you can't tolerate the contact lens options. Several surgeries are available, depending on the location of the bulging cone and the severity of the disease. Surgical options are:

• Intrastromal corneal ring segments (ICRS). During this surgery, your doctor inserts small, synthetic arcs into your cornea to flatten your cornea's cone, support the cornea's shape and improve vision. First, you are given local anesthetics around your eye. Your surgeon makes an incision in your cornea, either with a precision blade or a laser, and inserts the two arcs in specific locations based on your cornea's shape. The incision is closed with stitches, and a soft lens is placed over your eye to protect it as it heals.

  Although this surgery can restore a more normal corneal shape and halt the progression of keratoconus, many people still need to wear corrective lenses following the procedure. However, the surgery makes it easier to fit and tolerate contact lenses. Since the surgery is reversible, some people try ICRS before considering keratoplasty.

• Keratoplasty. If you have corneal scarring or extreme thinning, you will need a corneal transplant, called keratoplasty, which can be performed in a number of ways. Intralamellar keratoplasty is a partial-thickness transplant, in which only a section of the cornea's surface is replaced. Penetrating keratoplasty is a full-cornea transplant, in which an entire portion of your cornea is replaced.

  During a keratoplasty, you may have a general anesthetic, or just your eye may be numbed with a local anesthetic. Your doctor removes a button-shaped portion of your cornea, replacing it with a similar-sized button from a donor cornea. Stitches and a soft lens are placed to protect your eye as it heals. Recovery after keratoplasty can take up to one year, and you will likely continue to need rigid contact lenses to have clear vision.

Emerging treatments
A new treatment for keratoconus, called collagen cross-linking, is showing promise. After having riboflavin drops applied to your corneas, you receive 30 minutes of exposure to ultraviolet A (UVA) light. The procedure hardens and stabilizes the corneas, with the goal of preventing further thinning or bulging. The treatment is still in its testing phase and additional study is needed before it's widely available.

Most cases of keratoconus are not preventable, but there are some steps you can take to be sure you don't cause it yourself:

• Use care when rubbing your eyes. If you vigorously rub your eyes daily, you may be causing damage to your corneas in a way that can lead to keratoconus. Some people don't realize the extent of their eye-rubbing habit until a family member or friend points it out, so pay attention if someone has mentioned it. Try to wipe or rub your eyes gently and as little as possible.
• Follow instructions when wearing rigid contact lenses. If you wear hard contact lenses, be sure they've been fitted correctly and use them as directed to avoid damage to your eyes. Never use someone else's hard contact lenses.