Keratoconus

What is Keratoconus?

We see through the cornea, the clear central part of the front surface of the eye. The cornea normally has a round shape, like a ball.

Sometimes, however, the structure of the cornea is not strong enough to hold this round shape, and over time the normally round curve of the eye’s surface bulges outward like a cone. This condition is called keratoconus.

Keratoconus is usually detected in the teenage years or the twenties, though it can also begin in childhood. In some cases it is diagnosed later in life, but usually only when it is mild.

Keratoconus changes vision in two ways:

• As the cornea changes from the shape of a ball to the shape of a cone, its smooth surface becomes distorted. This is called irregular astigmatism, and it cannot be fully corrected with glasses.
• As the front of the cornea steepens, the eye becomes more short-sighted: distance vision is poor, and only nearby objects are seen clearly.

What are the symptoms of keratoconus?

The main symptoms of keratoconus are the following:

• Vision in one or both eyes gradually deteriorates, usually in the late teenage years.
• There may be double vision when looking with one eye only, even with glasses on.
• Bright lights appear to have halos around them.

Someone with keratoconus will notice their vision slowly becoming distorted. This change can stop at any point, or it can continue for several years. In most people with keratoconus, both eyes are eventually affected.

How is keratoconus diagnosed?

To establish the diagnosis of keratoconus, a corneal specialist must measure the curvature of the cornea. Several different tests can be used; the one used most often is called corneal topography.

Corneal topography measures the curvature of the eye’s surface and creates a coloured “map” of the cornea. Keratoconus produces very characteristic changes in the appearance of these maps, which allows the doctor to make the diagnosis.

Can keratoconus damage vision?

Left untreated, keratoconus can lead to permanent loss of vision. The changes in the cornea make it difficult for the eye to focus, with or without spectacles or standard soft contact lenses.

Keratoconus can also make laser vision correction surgery such as LASIK dangerous, as it can make the condition worse. Anyone with even a small degree of keratoconus should not have laser vision correction surgery, unless their ophthalmologist recommends it in very specific cases.

How is keratoconus treated?

There are several ways to treat keratoconus, depending on how advanced the condition is. In the early stages of the disease, vision can be corrected with ordinary glasses or soft contact lenses.

As the keratoconus progresses, irregular astigmatism may mean that glasses can no longer correct the vision, and the patient may need to be fitted with a special type of rigid contact lens.

For some patients, the disease reaches a stage at which they no longer have acceptable vision even with glasses or contact lenses. At this point, the doctor may recommend a corneal transplant, a surgical procedure to replace the cornea with one from a donor.

Additional treatments

Two additional treatments for keratoconus are implantable ring segments (often referred to as INTACS) and corneal cross-linking:

• Implantable ring segments are small devices inserted into the cornea to improve vision or to make it easier to fit contact lenses. In this procedure, which is performed under local anaesthesia (the patient’s eye is numbed with drops), the doctor creates channels in the cornea and inserts the rings into them. The rings help flatten the cornea and partially correct the conical shape caused by keratoconus.
• Corneal cross-linking uses ultraviolet light therapy to slow down or prevent the progression of keratoconus. In this procedure, the patient also receives local anaesthesia. Drops of a medicine containing riboflavin (vitamin B2) are applied to the eye for up to 30 minutes, after which the eye is exposed to ultraviolet light for up to 30 minutes. Cross-linking is designed to strengthen the bonds between the cornea’s collagen fibres and the surrounding proteins, which can help stop the cornea from steepening further.

Not all patients with keratoconus are candidates for these treatments. Your ophthalmologist can help you decide which of them, if any, could help you.

Does a patient with keratoconus need surgery?

Many patients with keratoconus will never need a corneal transplant. Corneal cross-linking is a significant advance in slowing or halting keratoconus, and it is particularly worth considering in young patients with early signs of the condition, so that loss of vision can be kept to a minimum.

Where vision can no longer be corrected with glasses or contact lenses, surgery may be recommended. Patients with keratoconus usually see better after corneal transplant surgery, although it may take more than a year for the vision to stabilise and for the patient to benefit from new glasses or contact lenses. Some patients still need special contact lenses after a corneal transplant to achieve their best vision.