Contact Lenses for Keratoconus
We often refer to Keratoconus as a coning of the cornea, in fact that is what the name means.
Actually it’s a bit more complicated than that and the major problem is the irregular shape of the cornea which distorts the light coming in to the eye.
Why not just wear glasses?
When I’ve had problem days with contact lenses I’ve often been asked “why don’t you just take them out and wear your glasses?”
In early or very mild Keratoconus spectacles may give a reasonable amount of vision correction, but if condition is moderate or advanced, then they don’t help much because of the irregular shape of the corneal surface. Basically the light hitting the eye is still distorted by the irregular cornea and vision is still blurred.
In fact Keratoconus is one of the few eye conditions where contact lenses work and glasses don’t.
Contact lens management of Keratoconus
Now, glasses may not work too well however, most people with Keratoconus can see reasonably well with contact lenses of some kind.
Rigid Gas Permeable corneal lenses
Rigid Gas Permeable (or RGP) corneal contact lenses are and appear likely to remain the main option for Keratoconus. They are what many people still refer to as ‘hard’ lenses, meaning that they keep their shape and have a solid feel to them. Corneal means that they fit over the cornea and cover an area usually slightly smaller than the coloured part of your eye.
They improve vision for the majority of people with Keratoconus because fluid is trapped between the lens and the corneal surface.
What this does is in effect create an artificial cornea without the irregularities and so light passes into the eye without being distorted.
Most people who wear lenses for conditions other than Keratoconus, wear soft (hydrogel) lenses.
Hydrogel lenses are very thin. They drape over the surface, so the front surface of the lens assumes the same irregular surface as the cornea without trapping a fluid reservoir.
Because of this they tend to form to the same shape as the cornea they are sitting on and the light is still distorted. For this reason they are not normally effective for more advance cases of the condition.
However, some hydrogel lenses have been designed specially for Keratoconus. They are designed to be thicker than regular soft lenses so they retain a more rigid shape. Because of this they compress the central cornea and partially trap some fluid in the same way that rigid contact lenses do.
These are therefore more ‘rigid’ than normal soft lenses and they do appear to be producing reasonable results with some types of Keratoconus.
Combinations of rigid and hydrogels
There are two ways that these can be combined:
A ‘Piggy-back’ fitting process is an RGP lens fitted on top of a hydrogel. This is often effective in improving comfort levels and can help RGP wearers through difficult times.
RGP / hydrogel fused lenses are an option if the discomfort is more due to lid sensation.
While these need careful monitoring they may be a suitable option for people who struggle with RGP
These lenses are also RGP lenses but instead of just fitting over the cornea they fit over the white part of the eye.
These have a number of advantages over RGPs in that they do not rest on the cornea, they produce less irritation and discomfort for the eye lid. They do not get dislodged so easily and they are less prone to irritation caused by dust etc.
They can be a bit scary to see, sometimes as much as 25mm (1 inch) in diameter and they may not be suitable for everyone.
So that’s my brief outline of lenses available.
Which one will you be using?
Your contact lens practitioner will advise what is best for you, but there is no reason why you shouldn’t have some input into that decision.
Sometimes contact lenses can be a nuisance. Stick with them if you can but don’t be disheartened if you have too many problems. There are other options open to you.
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