There are very few of the old type of “hard contact lens” wearers today due to improvements in other types of contact lenses. The old type of hard contact lenses were made of hard plastic material called Polymethylmethacrylate or “PMMA”. These lenses offered excellent durability and vision correction, but had two major limitations.
First, they were difficult to get used to wearing as they were not terribly comfortable. Second, they did not allow oxygen to reach the cornea easily and thus caused it to swell and cloud your vision.
Sometimes the swelling could become serious enough to cause a “scratched cornea” which was very painful and required you to stop wearing lenses for a while. Fortunately the cornea is very robust and it usually healed within a few days.
Even when worn successfully, rigid contact lenses caused the cornea to “mold” or change shape making it difficult if not impossible to wear glasses after removing the hard contact lenses.
For that reason rigid contact lenses were replaced by gas permeable contact lenses, which although still being rigid, allow oxygen to reach the cornea eliminating the possibility of swelling and usually allowing better vision with eyeglasses when they are removed.
They provide clear vision and last as long as 2-3 years, but because they are still rigid they are somewhat hard to adjust to. They are harder to insert and take out but correct most vision problems. Even with the advantages of gas permeable contact lenses over hard contact lenses, they still only account for about 15% of all of the contact lenses being worn in the United States today.