For Keratoconus sufferers the RGP or Rigid Gas Permeable lens is still one of the best forms of correction. However for some people they are a problem and one possible alternative the Scleral lens.
In people with Keratoconus the cornea (the front part of the eye)scleral lenses thins and distorts outwards into an irregular ‘cone’ shape.
It is this distortion of 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’.
Glasses, except for very early or mild cases, don’t work too well because they cannot be aligned properly to deal with the multiple focus points caused by the irregular shape of an eye with Keratoconus, Soft lenses (Hydrogel) are normally too thin and contour to the same shape as the cornea.
RGP lenses work because they keep their own shape and trap a layer of fluid between the lens and the cornea. The combination forms an artificial single surface that acts like a regular shape cornea.
Because RGP lenses are so small the edge of the lens can irritate the inner surface of the eyelid and this can make wearing them uncomfortable.
Also the lenses can pop out quite easily, particularly if the cornea of the eye with Keratoconus is quite steeply curved (think about balancing a saucer on the end of a rugby ball).
Also RGP lenses can be a problem in very dry and or dusty conditions because dust can get behind the lens or around the edge of the lens quite easily.
An alternative for Keratoconus is a Scleral lens.
This is also a rigid lens but is much larger in diameter than a normal RGP. Where the normal RGP is slightly smaller than the coloured part of your eye and fits only on the cornea, a scleral lens is designed so that the edges sit on the sclera or white part of your eye.