Different choices of contact lenses
Contact lenses are worn usually by those who hate the load of a pair of spectacles on their eyes, ears, and nose. Hard contact lenses proved to be highly risky. Therefore, we had soft contact lenses developed. However, there is another thin category of contacts, which is called rigid gas-permeable lenses.
They have the word rigid; however, they must not be confused with hard contact lenses. Rigid Gas-Permeable lenses were introduced in the 1970s and are a relatively newer technology than soft contacts.
RGPs incorporate silicone in them. Silicone makes them more flexible than PMMA, and oxygen flows freely through the silicone. Two drawbacks of hard contact lenses were the rigidity, and that oxygen didn't pass through. Eyes, like most body parts, need oxygen. Therefore, the PMMA was stopped. RGPs cover both the negatives by using silicone instead of PMMA.
Aspheric lenses transmit oxygen most freely, even more than soft contact lenses. Some silicone hydrogen lenses do provide comparable oxygen transmission, however. They are less expensive than soft contacts and can be used for longer periods. They are comparatively easier to clean. Also, they provide better vision, durability, and deposit resistance compared to soft contacts.
Some other benefits of the Aspheric lenses are the following-
1) They retain their shape when you blink because they are made of stiff material. Hence, it provides a crisper and better vision.
2) They are extremely durable. One can break them, but can't tear them, unlike soft lenses which are not durable.
3) They don't have materials which contain water. Proteins and lipids of the eyes have an affinity for water, and therefore they stick to soft lenses, but not to RGPs generally.
While these all are the benefits of aspheric over Soft lenses, there is a particular drawback. The first one is the ease of use. Soft lenses are easiest in usage. While RGPs require an adaptation time and are still not that easy to wear every day. After Frequency 55 discontinued, it becomes quite difficult to choose a suitable aspheric lens, but other manufacturers come with some superb lenses for the aspheric lens users.
To get the best results, one needs to wear aspheric contact lenses regularly, not necessarily daily; else they won't be comfortable. However, soft contacts are suitable whenever they are used. Also, when aspheric is removed, vision remains blurry, even after using spectacles, which doesn't happen with soft contacts.
So, contact lenses have a number of benefits, with a few drawbacks. One must always consult a doctor before choosing a type of contact for them.