Contact Lenses
Bausch & Lomb, incorporated as Bausch & Lomb Optical Co. in 1908, has used materials from Plexiglas to silicone hydrogels to help people make eye contact.
Credit: iStock
The first contact lenses were blown of glass in the 1880s and rested on the white of the eye rather than covering just the cornea; they could be worn for a few hours at most. Plastic lenses were introduced in the 1930s. The first lenses with mass appeal were smaller lenses that covered just the cornea and were made from poly(methyl methacrylate) (PMMA), also known as Plexiglas. Popular through the 1960s, PMMA contacts were notorious for popping out at inconvenient moments. Softer, more comfortable lenses made from poly(hydroxyethyl methacrylate) (poly-HEMA) were introduced in the 1970s.
A key thing to know about eye anatomy is that the cornea does not have blood vessels. Consequently, corneal cells get nutrients from tear fluid and from gelatinous material called the aqueous humor, which is located on the inside of the eye. Corneal cells get their oxygen directly from the air. A big drawback for PMMA and poly-HEMA lenses was that neither is permeable to oxygen. This became a particular problem for the softer poly-HEMA lenses because wearers found them more comfortable than rigid PMMA lenses and people therefore wore them longer. In extreme cases, oxygen deprivation to the cornea can lead to growth of blood vessels into the cornea, threatening eyesight.
From the 1970s to the 1990s, much of contact lens research focused on improving oxygen permeability of lens materials. This effort first led to rigid gas-permeable lenses that incorporated a small amount of silicone for flexibility and oxygen permeability, but many wearers found it hard to adjust to the new lenses.
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Excerpted with permission, Chemical & Engineering News
Copyright © 2008 American Chemical Society