Last year approximately 34 million people in the U.S. wore contact lenses, according to the Contact Lens Council . These lenses need cleaning daily. Fewer than 15 percent of contact lens wearers use what are called rigid gas-permeable lenses, which can last for years if taken care of properly. David T. Grubb , a materials scientist at Cornell University, describes their molecular structure as open, with large gaps through which oxygen can pass. Hydrogel polymers, in contrast, are hydrophilic, absorbing or attracting water in amounts that vary from commercial brand to brand.
Water moving through the molecular structure of soft lenses carries oxygen with it.
When the eyelids are closed, contacts block the ow of oxygen to the clear, delicate cornea, hindering routine tissue repair. The protein deposits can shelter pathogens, increasing the chances of infection. The challenge in building an extended-wear lens, Grobe says, is finding the right polymer mix. Tears are made mainly in the lacrimal gland. Mostly water and salt, they also carry proteins, glucose, potassium, sodium, calcium, chlorine, bicarbonate, ammonium, nitrogen, citric and ascorbic acids, lysozymes, and other substances.