The transition from the Hard (PMMA) to Rigid Gas Permeable (RGP) contact lenses.
After the introduction of the corneal hard lens, the contact lens wearers were introduced to the “Holy Grail” of contact lenses: the RGP lenses. It was supposed to be a hard lens made from a “breathable” plastic. However the amount of oxygen transmission was not very high and it soon became obvious that lenses with high powers and therefore thicker lenses did not benefit greatly from this new material.
In matter of fact the RGP lenses tended to attract protein deposits in the form of crystal molecules. So after wearing them for a few weeks the lenses became more and more irritating. In the beginning not many practitioners knew the source of the problem. Very often this thin layer of protein deposits from the tear film was not visible to the naked eye. On top of all this the rate of protein depositing depended on the individuals’ eyes. Some contact lens wearers did not experience any depositing while others would start to get irritated eyes within a week of wearing these new lenses.
A lot of time was then wasted by trying to refit the eye with a new RGP lens with different parameters. Slowly the optometrists started to realize that the RGP lenses needed a strict cleaning regime with special protein removing agents and wet overnight storage in contact lens containers to keep the lenses comfortable. For many previous PMMA lens wearers this was an extra burden and in many cases this strict cleaning was not adhered to. A result was that RGP contact lens wearers had to re-visit the optometrists frequently and the end result was frustration and in many cases a refit to PMMA contact lens.
I have seen many cases of successful PMMA wearers being converted to RGP with less than satisfactory results. I even know of optometrists who thought that because of this so-called breathable lens material they now could increase the diameter of the contact lenses as to obtain better vision under low light conditions. The poor contact lenses wearer now started to get problems because to remove the lenses from the cornea became harder. Because of the a-spherical nature of the corneal surface the contact lens would now fit much tighter on the eye with the larger diameter lens. Corneal oedema would result and the optical correction of the eye would alter.
A new replacement lens had to be made and more and more problems would result. A lot of confusion among the contact lenses practitioners existed during the years of the late seventies and early eighties. As a result a lot of spectacle wearers were put off to switch to contact lenses. And even up to now there is still the concept that contact lenses might be difficult to get used to or might be irritating to the eyes.
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Tags: contact lens, contact lenses, eye vision
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