Keratoconus

Keratoconus is a condition in which the cornea, normally a smooth dome, gradually thins and bulges forward into a cone. Because the cornea does most of the eye's focusing, the irregular shape blurs and distorts vision. It usually begins in the teens or twenties, affects both eyes, though often unequally, and tends to progress for 10 to 20 years before settling. A treatment called cross-linking can now stop it from getting worse, so finding it early matters.

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What it feels like

• Blurred vision that glasses do not fully correct
• A prescription that keeps changing, with increasing astigmatism
• Ghost images or doubling seen with one eye
• Streaks, flares and halos around lights, especially at night
• Glare and light sensitivity
• Eye strain and headaches

Who gets it

• It starts in adolescence or early adulthood
• Eye rubbing is the most important factor that can be changed. Hard, habitual rubbing weakens the cornea.
• Allergies, eczema and asthma, which lead to rubbing
• A family history
• Conditions such as Down syndrome and sleep apnea, and floppy eyelids

How it is found

A scan of the cornea's shape and thickness (corneal topography or tomography) shows keratoconus long before it can be seen at the slit lamp. It is quick and painless. It is done whenever astigmatism is rising or irregular, and for everyone considering laser vision correction, because LASIK is not safe in a cornea with keratoconus.

Stopping it: cross-linking

Cross-linking, specialty lens fitting and keratoconus surgery are done by cornea and contact lens specialists. Your eye doctor will refer you.

Corneal cross-linking is the one treatment that addresses the cause. Vitamin B2 (riboflavin) drops are soaked into the cornea, which is then exposed to ultraviolet light for several minutes. This creates new bonds between the cornea's fibers and stiffens it.

• It halts progression in the great majority of eyes.
• It does not reverse the cone or remove the need for glasses or contact lenses, which is why it is done as soon as progression is confirmed.
• It is an outpatient procedure with numbing drops. The eye is sore, watery and light-sensitive for several days while the surface heals under a bandage contact lens, and vision takes weeks to months to settle.

Stop rubbing your eyes. Treat the itch instead: see Eye Allergy.

Seeing well

• Glasses or soft contact lenses in early keratoconus
• Rigid gas-permeable lenses, which replace the irregular surface with a smooth one
• Scleral lenses: larger rigid lenses that vault over the whole cornea and rest on the white of the eye, with a layer of fluid underneath. They are comfortable and give the best vision in moderate and advanced keratoconus.
• Hybrid lenses, with a rigid center and a soft skirt

Fitting these takes a specialist and several visits. It is worth it: most people with keratoconus see well with the right lens.

Surgery

• Small plastic ring segments placed in the cornea can flatten the cone in some eyes.
• A corneal transplant is needed in a minority of people, when the cornea is scarred or too steep for any lens. See Corneal Transplants.

A sudden change

Rarely, the inner layer of a very thin cornea splits and the cornea suddenly swells, with a sharp drop in vision and a white haze. This is called hydrops. It is not dangerous to the eye and settles over weeks to months, but it should be seen promptly.

Questions worth asking

• Is my keratoconus progressing?
• Should I have cross-linking, and in which eye first?
• Which kind of contact lens would suit me?
• Should my children or siblings be checked?