Keratoconus

Keratoconus is a disease of the cornea involving a distortion of the corneal surface. It very often developes in teenagers as the once near spherical cornea extends and becomes cone like.

Methods of Correction:

Spectacles
In the early stages spectacles can be used to correct the refractive error of the eye as it becomes myopic (short sighted) and astigmatic (egg shaped). However, as the disease progresses not only does the myopia increase but the astigmatism becomes more and more irregular. The result of this is that it becomes increasingly difficult to correct the eyesight with spectacles.

Soft Contact Lenses
With the increase in myopia and astigmatism the best way to correct the eyesight is by using a contact lens. Soft lenses can work in some cases but often don’t give good vision because the irregular shape of the cornea is taken up by the soft contact lens. I have obtained good results in a few cases using a toric soft contact lens which is especially made to correct astigmatism but more often than not this does not give good visual acuity once the cone has developed beyond the early stages of Keratoconus. Keratosoft (developed by UltraVision) is a soft lens designed to correct the keratoconic cornea by using a thick periphery and “vaulting” over the cone. We hold a fitting sst of these lenses in the practice.

Gas Permeable Contact Lenses
Traditionally this has been the lens of choice when trying to correct Keratoconus. The ridgid lens sits on top of the cone and tears fill in the spaces left by the irregular nature of the cornea. The result is that the “bumpy” cone of the cornea is replaced by a smooth optical service and a good focus can be produced. The big downside is the discomfort of the lens. Many patients learn to tolerate the initial discomfort and eventually can wear the lenses for several hours at a time and sometimes all day. A patient with mild Keratoconus can be fitted with a standard design contact lens but as the cone progresses more elaborate designs are required to try to match the conical cornea.

Hybrid Ridgid Contact Lenses with a Soft Skirt
This type of lens has been around for a while. It was produced under the name of “Softperm” by CibaVision but was then discontinued. A similar lens is now produced by Synergeyes with the name of “Clearkone”. The central part of the lens is of ridgid gas permeable material and hence enables good visual acuity. The peripheral portion of the lens is made of soft lens material and helps to give comfort similar to a soft contact lens. I recently fitted a patient (August 2011) and both the patient and I were quite excited by the results. As a consequence I now have a “Clearkone” fitting set kept in the practice.

Surgery
As the cone progresses it can begin to scar and become opaque. Eventually fitting any sort of contact lens becomes very difficult and as a last resort surgery is required. This involves a section of the cornea being removed and a donor cornea being implanted.

Cross Linking
Cross linking is a relatively new treatment which does not cure keratoconus but strengthens the bonds between the corneal fibres in the stroma. The treatment involves stripping the outer layer (epithelium) away, instilling drops of Riboflavin and using UVA radiation. There is evidence to show that this slows down or stops the progression of the cone.

More information on Cross Linking can be found on Wikipedia.