Keratoconus

An eye showing a corneal bulge

In Keratoconus, the cornea bulges, causing an irregular curvature.

A normal Cornea

By comparison a normal Cornea shows a more regular curvature

Keratoconus (literally meaning “conical cornea”) is a condition in which the cornea, the clear part at the front of the eye becomes thinned and weaker near the centre. This weakening causes it to bulge slightly, which alters the curvature, and therefore the power. This causes a power variation across the cornea, which may not be adequately corrected with spectacle lenses.

There has been much investigation into the cause of Keratoconus, but while there was thought to be a genetic predisposition- Indian and Pakistani Asians are more likely to have it, a study conducted in Moorfields Eye Hopsital in London found that the only factor which increases the risk is eye rubbing! Asians are more likely to suffer Atopic conditions, such as eczema and allergies, and likely suffer more and at a younger age, which mean they are more likely to have itchy eyes, and thus are more likely to be eye rubbers. In truth, the cause of Keratoconus is still uncertain.

This author, and most ophthalmologists, would always be trying to prevent tired children from giving their eyes a good rubbing! If your child is an eye rubber, it would be worth investigating if they do suffer from allergies, and if they do, perhaps considering eye drops to prevent inflammation as this is the cause of the itching.

Since the advent of laser eye surgery, it has become apparent that Keratoconus is perhaps more common than previously suspected, but many cases found have been “sub-clinical”- not evident in a routine eye test and asymptomatic. However these patients would not be suitable for laser treatment, as thinning the cornea with a laser would only likely weaken it further.

The traditional treatment for Keratoconus was

  1. Do nothing until or unless vision with spectacles did not reach an acceptable standard.
  2. Fitting of contact lenses usually Rigid Gas Permeable (RGP) type. Becasue the lens is rigid and holds its own shape, it floats on a very thin layer of tears, and the eye/contact lens now has a regular front surface again, allowing for sharper vision.
  3. If contact lenses were poorly tolerated, or became unstable because of the shape of the cone, a corneal transplant would be considered, where the irregular cornea is removed and replaced by a donor one. Transplantation sometimes becomes necessary due to scarring of the cone- the bulging area can develope splits in the corneal back surface (the Endothelium), and because the endothelium controls the hydration of the cornea, it can lose its ability to regulate water content. Repeated episodes of this occurrence can cause scarring.

There are some very effective new treatments which may arrest or at least delay progression of Keratoconus. These are suitable for consideration as long as the cornea is not too thin, and is clear (without scarring).

Corneal Collagen cross-linking has been shown to be effective at strengthening the weakened area, and often can result in a reduction of the corneal bulge. This involves applying Riboflavin drops to the eye and using a UV laser to activate the solution. It works in a similar way to a hair perm, where the hair proteins are partially dissolved and then reform , where they then hold their new curled shape.

This procedure may be done in isolation, or sometimes is combined with intra corneal rings (INTACS)- two semicircular plastic rings implanted into the cornea, which can again reduce the irregularity. The newly flattened cornea can then be cross-linked in an attempt to keep it in it’s new improved shape.

These new treatments are done under local anaesthetics, and whilst medium term results seem very good, it will take many years yet before the long term efficacy is proven, though as the intacts are easily removed should it become necessary, there is unlikely to be any long term harm from these procedures.

 

Local eyecare for all the family

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