PMMA Contacts Are The Older Hard Contact Lenses
Are you the wearer of the older hard PMMA contacts or did you used to wear them? Polymethyl methacrylate (PMMA) contact lenses were the first contact lenses used to correct vision. They are not used anymore very often.
What were the advantages of the PMMA lenses?
PMMA lenses are made of a brilliantly clear, lightweight, rigid polymer with outstanding optical properties. Among its successes were: Excellent optical properties Durability Biocompatibility (can coexist with living tissue without causing harm) Superior dimensional stability Hardness (helped mask a good amount of astigmatism, usually less than 2.00 diopters) Wettability Resistance to deposition of protein and other foreign material in tears Easy to fabricate Low cost
If they were so great why are they not used very often anymore?
The low oxygen permeability of PMMA lenses greatly limits their use. The low oxygen permeability of these lenses caused complications of the cornea of the eye.
The cornea is the transparent tissue in front of the colored part of the eye. Complications included the swelling of the cornea and central corneal clouding.
Luckily these complications resolve after the cornea is exposed to oxygen. These complications along with complaints of discomfort from some patients prompted the development of more comfortable lenses that could be worn for an extended period of time.
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