What is it?
Keratoconus (sometimes called conical cornea) is a progressive condition that produces corneal thinning and distortion causing blurred and distorted vision. The inferior cornea gradually bulges forward and takes on a cone shape. It is quite rare (the prevalence is about 1 in 2000) but New Zealnd has a high incidence of keratoconus by world standards.
What causes it?
The exact cause is unknown but we know iit has acquired and inherited components. Keratoconus can be associated with conditions such as allergies, asthma and eczema. There is a strong link to eye rubbing in many sufferers. Onset is usually between the ages of 10 and 25 years, and it is rare for this disease to progress after age 40.
What happens next?
As the cornea gradually becomes more cone-shaped, the vision blurs and becomes distorted. Monocular diplopia [double vision in one eye] and ghost images are common. In mild keratoconus good vision can be achieved with glasses or soft contact lenses, but in advanced cases specially designed rigid gas permeable lenses are required.
In most cases the condition will stabilise but in about 15% of case the condition progresses to a point where contact lenses can no longer be used and corneal graft ( transplant) is necessary. While there is are risks associated with this type of surgery, the success rate for corneal grafts is extremely high. Contact lenses may still need to be worn after surgery and there are special designs for post graft lens fitting.
Contact Lens Fitting for Keratoconus
A contact lens for keratoconus is designed so that its front curve is spherical (to provide undistorted vision) but the back curves are tailored so the lens stays on the unusually shaped cornea. Fitting contact lenses for keratoconus patients is challenging but New Zealand has some experts in this field and there are a number of lenses especially designed for keratoconic corneas. A past president of the CCLSNZ named Paul Rose has designed a series of these lenses. The eponymous Rose K is manufactured both here and overseas.
Contact lens wearers with keratoconus need more frequent follow up visits than other wearers because their corneal shape can change quite quickly. Their lenses will need to be refitted regularly to maintain good vision and lens comfort. A poorly fitting lens can cause scarring on the eye surface as well as discomfort and poor vision. In New Zealand the Ministry of Health provides a small subsidy for lenses and fitting fees for some keratoconus patients – ask your contact lens practitioner about this.
Treatment for Keratoconus
In early keratoconus a procedure called Corneal Crosslinking can be useful. This procedure is designed to halt the progression of keratoconus by making the cornea more rigid and less likely to distort. The therapy involves using B12 or riboflavin drops and UV light to stiffen the middle layers of the cornea. It does not reverse any change that has already occurred but prevents further change and is most useful in teenage patients.
There is a hereditary component in keratoconus. If you have keratoconus and have children, you should have their eyes tested regularly.