Keratoconus
What is it?
Keratoconus is a progressive condition that produces corneal thinning and an irregular shape, causing blurred and distorted vision. The thinning causes the cornea to gradually bulge forward taking on a cone shape. Keratoconus can occur in one or both eyes, and is often asymmetric.
Keratoconus is quite rare (the prevalence is about 1 in 2000) but New Zealand has a high incidence of keratoconus by world standards.
what causes it?
The exact cause of keratoconus is unknown, but we know it 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.
Unknown Cause
Strong Link to Eye Rubbing
Onset between 10-25 years old
Signs & Symptoms.
As the cornea gradually becomes more cone-shaped, the vision blurs and becomes distorted. Double vision in one eye and/or ghost images are common. Often, keratoconic patients experience changes in their spectacle prescription every time they visit their optometrist. Glare and light sensitivity can also occur.
In mild keratoconus good vision can be achieved with glasses or soft contact lenses, but in moderate cases specially designed rigid gas permeable (RGP) lenses are required.
Double Vision or Ghosting in One Eye
Frequent Spectacle Prescription changes
Specialty RGP Contact Lenses
Specialty Contact Lens Fitting.
Because the cornea is cone-shaped and distorted the lens fitting in a keratoconic cornea is considered specialty. Different specialty lenses vary in design, but essentially they all provide three things. Firstly a back surface that is stable on the irregular keratoconic cornea. Secondly there is a middle tear fluid layer behind the lens to cushion and fill the gap. Lastly there is a regular shaped front surface to provide and restore clear vision. .
Fitting contact lenses for keratoconus patients is challenging with a number of lenses especially designed for keratoconic corneas. New Zealand has some experts in this field, including a past president of the CCLSNZ named Paul Rose who has designed a series of keratoconic lenses, which are used worldwide.
Contact lens wearers with keratoconus need more frequent follow up visits because keratoconus can change quite quickly. Lenses often need to be refitted regularly to maintain good vision, lens comfort, and eye health. A poorly fitting lens can cause scarring on the eye surface as well as discomfort and poor vision.
In New Zealand your local district health board provides a small subsidy for lenses and fitting fees for some keratoconus patients – ask your optometrist about this subsidy.
Treatment
In early keratoconus a procedure called Corneal Crosslinking can be an option. This procedure is designed to halt the progression of keratoconus by making the cornea more rigid and less likely to distort. 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 to see if early treatment could be of benefit.
About 15% of ketatoconus cases will progress to a point where corneal graft surgery is needed. In late stage keratoconus corneal graft surgery can help restore vision, and surgery often has a high rate of success. After surgery specialty contact lenses may still be needed for some people.