KERATOCONUS
Keratoconus is a condition in which the regular shape of the cornea is altered. The cornea is the clear, front window of the eye. It normally has a spherical dome shape and it helps to focus light onto the retina. The cornea bulges outward creating a cone-like shape.
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The cornea is made up of hundreds of layers of collagen fibres. In keratoconus these fibres are weakened and thinned. The specific cause is not known. Genetic factors play a role and 10% of people with keratoconus have a family member with this condition. Keratoconus is often associated with allergic conditions such as hay fever, eczema and asthma. Eye rubbing has been found to be an important factor, so you should not rub your eyes. The incidence of keratoconus in the general population is about 1 in 2000.
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When suspected, a computerised scan (topography or pentacam) is done. This produces a three dimensional map of the cornea revealing its shape, thickness and curvature. This can detect keratoconus at an early stage.
Symptoms:
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Blurring and distortion of vision
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Increasing short sightedness and astigmatism
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Frequent glasses prescription changes
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Double vision
These symptoms usually first appear in the late teens and early twenties. Keratoconus may progress for 10-20 years and then slow or stabilise. Each eye may be affected differently. Occasionally, keratoconus can advance rapidly, causing the cornea to become white and swollen (called hydrops). Scar tissue can also develop and this causes the cornea to lose its transparency.
Pentacam topography scan of a cornea with keratoconus. The red area is where the cornea is bulging excessively causing astigmatism.
How Is Keratoconus Treated?
During the early stages, vision can be corrected with glasses. As the condition progresses, hard gas permeable contact lenses (RGP lenses) or scleral contact lenses are needed. These contact lenses “ride” on the tear film of the eye.This helps to make the corneal shape more normal and hence gives better vision. These need careful fitting and frequent visits to the optometrist to maintain good vision. Refractive surgery such as LASIK cannot be performed on people with keratoconus as it can make the condition worse.
You should refrain from eye rubbing as this can aggravate the condition.
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Corneal Collagen Crosslinking
This is a treatment for keratoconus and needs to be done at an early stage before the corneas are too thin or scarring has developed. In a normal cornea, the collagen fibres are linked together and this helps to provide strength to the cornea. These links are deficient in keratoconus. Corneal Collagen Crosslinking treatment creates more links between the fibres, resulting in increased corneal rigidity of up to 300% in experimental studies.
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The procedure is performed in Dr Anderson’s rooms. Anaesthetic drops are applied and the epithelium (surface layer) of the cornea is gently removed. Riboflavin drops are applied and the cornea is then exposed to a controlled amount of ultraviolet light for 10 minutes. A bandage contact lens is placed on the eye for 3-4 days to facilitate healing. The eye will be uncomfortable for a few days.
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Crosslinking is a major advance in the treatment of keratoconus. For most people, only one treatment is required. Sometimes the effect can wear off after a number of year and it may need to be repeated. Although crosslinking will not improve your spectacle prescription much, it most people it will help stabilise the cornea and prevent or delay the need for corneal transplantation.
Surgery
When good vision is no longer possible with contact lenses, a corneal transplant may be recommended. This surgery is only necessary in about 20% of patients with keratoconus.
In a corneal transplant, the ophthalmologist removes the diseased cornea from the eye and replaces it with a healthy donor cornea.
The operation is performed in hospital under general anaesthesia and involves an overnight stay. The new cornea is sutured in place using 16 nylon stitches. These remain in place for a year or longer.
Some stitches may be removed from tine to time to help normalise the shape of the cornea and reduce astigmatism. Although you are able to function normally within a few days, healing takes much longer.
While a corneal transplant will remove the distorted, thinned and scarred cornea of keratoconus, it will not provide perfect vision without correction. Most often some astigmatism remains but this is much more easily treated with glasses or contacts than before the surgery.
Most corneal transplants are highly successful and there is a marked improvement in vision. Rejection can sometimes occur so careful follow up and diligent use of eye drops is important.
The is a critical shortage of local corneal donors in South Africa and unfortunately a long wait can be expected. An alternative that is often used is to import donor corneas from the USA. These can be acquired within a few days.