Keratoconus is a progressive condition that where the cornea thins causing shape distortions. This therefore causes blurred and distorted vision. While it is generally uncommon (the prevalence is about 1 in 2000), New Zealand has a high incidence of keratoconus by world standards.
The exact cause is not known but we know it has both acquired and inherited genetic components. Keratoconus may be associated with conditions such as allergies, asthma and eczema. There is also a strong link to eye rubbing in many people. The typically age of onset is between the ages of 10 and 25 years. It is rare for this condition to progress after age 40. Keratoconus may also be associated with other conditions like Down’s syndrome.
In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually appear in the late teens or early twenties. Keratoconus may progress for 10-20 years and then slow in its progression. Each eye may be affected differently and one eye may have very poor vision while the other eye retains perfect vision.
As keratoconus progresses, the cornea bulges more and the vision may become more distorted. The cornea is weaker than the normal cornea and may be damaged by minor trauma. For this reason people with keratoconus should not participate in contact sports.
There is a hereditary component in keratoconus. Studies have provided evidence to suggest a genetic basis for keratoconus. Up to 50% of family members of patients with keratoconus have subtle signs of early keratoconus. If you have keratoconus and have children, you should have their eyes tested regularly.
As the cornea gradually becomes more cone-shaped, the vision blurs and becomes distorted. In the early stages vision may be corrected with normal glasses lenses.
We recommend that people with early keratoconus or a family history of keratoconus are screened regularly. Should it be found that the condition is progressive it is possible that the progression can be slowed by a collagen cross linking procedure. This is now available at your Ophthalmologist or at Wellington Hospital.
Monocular diplopia [double vision in one eye] and ghosting are common. In mild keratoconus good vision can be often be achieved with glasses or soft contact lenses. But in more advanced cases, specially designed more 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 are no longer appropriate and a corneal graft (transplant) is indicated. Although there is are risks associated with this type of surgery, the success rate for corneal grafts is extremely high. It is important to realise that contact lenses may still need to be worn after surgery. There are special designs for post graft lens fitting
Special contact lenses for keratoconus are designed so that the front curve is spherical (to provide normal undistorted vision). The back curves are tailored to fit the unusually shaped cornea. Fitting contact lenses for keratoconus patients is challenging in that lenses generally need to be custom made. In these images below the green represents the tear film underneath the contact lens.
Today there are many different lens types and strategies. At Total Eyecare we are constantly testing and exploring lenses from all over the world. New Zealand has some experts in this field and one of the most successful lens designs was developed right here. 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 us about this.