UK Keratoconus Self-Help and Support Association

Do RGP's, soft lens, scelerals equally or differently allow oxygen?

I don't really know, but I could never wear soft lenses because there was a problem in my eye with oxygenation. I don't have that problem with RGP corneal lenses, and when i had a scleral there was a fenestration drilled next to my cornea so that oxygen would pass easily to my eye.
I'd be interested to see any study on vascularisation when wearing soft lenses for KC

Hi Lou

It doesn't really simply depend on the contact lens type - it depends on the design and the material.

For example, RGP's are called that because RGP stands for Rigid Gas Permeable. The actual correct terminology for these kind of lenses is "corneal" and when they were first invented, the plastic they were made from was called PMMA and it had ZERO oxygen transmission. Some of you may be old enough to remember them and I know some people still wear these to this day. You could get away with this because the lenses are smaller than the cornea and oxygen can still get into the cornea via the area not covered by the lens.

Eventually rigid contacts were made from plastics that did allow oxygen transmission and you can now get a range of materials that transmit different amounts of oxygen.

Scleral lenses followed the exact same development. However, they have an issue in that there is not much exchange of tears from outside the lens to under the lens because of the sheer size of the lenses and even with gas permeable sclerals, sometimes holes have to be drilled into them to allow direct access to atmospheric oxygen.

Soft lenses were made straight away from materials that did transmit oxygen, but the amount of oxygen transmitted was low. Again, over the years, there have been improvements in materials and you can now get some materials that transmit an incredible amount of oxygen.

However... this is not the full story because the amount of oxygen reaching your eye also depends on the thickness of the lens. A lens made from a highly oxygen transmitting material may not actually be that good for the eye if the lens is very thick.

Additionally, there is a limit to the amount of oxygen can absorb - over a certain amount, it doesn't matter how much more oxygen you deliver to the cornea, no more will be absorbed.

So, there is no straightforward answer to the question, it all depends on the individual case, lens fit and lens design.

In answer to Andrew's comment; most soft lenses for KC years ago were made from low DK (Low oxygen transmission) hydrogel materials and vascularisation was not uncommon. Same applied to hybrid lenses with Low DK soft skirts.

Lynn

Nowadays, most of the soft lenses are manufactured from silicon hydrogels or high water content soft lens materials both of which let through a lot more oxygen and vascularisation is rare unless patients really, REALLY overwear lenses.

yes I have some looping vessels but not in the graft and understand that over wear is best avoided. I thought vessels could be sealed off with a laser if threatening a graft but apparently not