Keratoconus and RGP Lenses

RGP lenses are still the most common form of correction for Keratoconus, so why are these lenses so successful and what are the downsides to them?

Keratoconus is a disease of the cornea, which is the clear front surface of the eye. In people with Keratoconus the cornea thins and distorts outwards into an irregular 'cone' shape.

It is this distortion or the eye that results in reduced vision as the light entering the eye can not be properly focused onto the retina and this causes blurring and 'ghosting'.

Spectacles and soft contact lenses (Hydrogels) are of limited use for more advanced Keratoconus as they do not correct the distortion of the eye.

Glasses cannot be aligned properly to deal with the multiple focus points caused by the irregular shape and soft lenses tend to be thin and contour to the same shape as the cornea (although there are some thicker soft lenses that are better at keeping their own shape and therefore go someway towards the benefits of RGP lenses).

RGP or Rigid Gas Permeable contact lenses are small lenses, normally slightly smaller in diameter than the coloured part of your eye.

As the name suggests they are rigid, they are also sometimes described as hard lenses.

Because they are rigid they keep their own shape when fitted to the eye. Because of this they also trap a layer of fluid (tears) between the surface of the corneas and the contact lens.

The combination of your cornea, the fluid and the RGP lens forms a single refractive surface that. To all intents and purposes, is like an artificial cornea. This artificial cornea has a regular shape and is able to direct light so that it can be focused properly on the retina. Blurring and 'ghosting' are removed, or at least reduced, and vision is improved.

Of course there are some downsides to RGP lenses.

Their rigid nature makes them less comfortable than soft lenses. This can be as a result of pressure on the cornea or as a result of the edge of the lens rubbing on the inner surface of the eyelid.

They are also more prone to discomfort in dry or dusty conditions..

Where the curve of the cornea is very steep the lens balances on the eye with a large gap around the edge. Think of balancing a shallow bowl on the end of a rugby ball. This can make the edge even more prominent, which of course reduces the comfort level and also make it much easier for the lens to be dislodged and lost.

Despite these downsides the majority of people with Keratoconus will get good correction with RGP lenses and they are definitely worth persevering with.

If you are new to them they may take some time to get used to, and it may be necessary to 'build up' the time you wear them over a number of weeks.