Advantages and disadvantages of gas permeable lenses
Also called RGPs, rigid gas permeable or oxygen permeable lenses, gas permeable (GP) contact lenses are less widely known than soft lenses. RGPs are different from “hard” contact lenses, which have disappeared today, although they were popular before the invention of soft lenses by Bausch & Lomb in 1971. PMMA hard lenses are uncomfortable and prohibit oxygen from passing through the lenses.
Advantages of GP lenses
Invented in the late 1970s, GP lenses contain silicone, which is more flexible than PMMA and allows more oxygen to pass through, bringing more comfort and better vision. Oxygen can be easily transmitted and reach the surface of the cornea. This is widely recognized as the most significant improvement brought by GP lenses. In addition, GP lenses are suitable for most astigmatic patients because they can come in cylinder powers up to 2.50D. But they are less helpful for people with a heavy astigmatism.
GP contact lenses also have some other advantages, such as more durable and deposit resistant, easier to clean, and less expensive. In terms of durability, gas permeable contact lenses are usually designed to last 3 or 6 months. And some brands even recommend annual replacement. In addition, rigid gas permeable contacts usually bring better visual acuity because they do not deform under eye blinking. They can stay at the center part better than other types of lenses.
Who are target users?
GP lens is the right solution for certain groups of people who are unsatisfied with soft lenses, such as vision fussy individuals, people with astigmatism, presbyopia or keratoconus, or individuals after a refractive surgery. GP lenses offer the best answer to bifocal lenses for people with presbyopia. Ortho-k lenses are also use GPs.
Nevertheless, GP lenses are not flawless. They require a regular use so as to get most comfort and a longer time to adjust, which never happen to soft lenses. In fact, both soft and GP lenses bring long-term comfort. The reason for the adaption period associated with gas permeable lenses is that these lenses are relatively smaller than soft lenses. During eye blinking, it is easier to experience initial “lens awareness”. GPs may still cause blurry eyes when they are removed, but the situation will soon disappear. GP lenses also need more careful cleaning and storing since they last for a long time.
Combinational contact lenses
Currently, new versions of lenses that combine the visual clarity from GPs and comfort from soft lenses are available. They remove the most noticeable obstacle for GPs. These special lenses are used for presbyopia, keratoconus and LASIK recovery.
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