There are all sorts of contact lenses on the market, from rigid, gas-permeable lenses that are relatively stiff and that you change once a year to soft, very flexible disposables that you change every day, every two weeks, once a month or once every three months. The US Food and Drug Administration, which must approve contact lenses for marketing, believes all these devices are safe and effective if used according to manufacturers’ instructions, a spokeswoman said.

“Most people can safely wear disposable contact lenses for years. We have some patients in their 90s who have been wearing contacts for decades,” said Jill Beyer, an optometrist and clinical director of the contact lens service at the Massachusetts Eye and Ear Infirmary.

Of all the contacts now available, “the one-day disposable is the safest,” said Elliott Myrowitz, an optometrist at the Wilmer Eye Institute at Johns Hopkins University in Baltimore. That’s because you are putting in a fresh, sterile lens every day, he said, thus minimizing the risk of infection and the buildup of proteins from tears on the lens.

Other disposables are OK also as long as you soak the lenses in the solution that your optometrist suggests to “kill any bugs round the lens,” said Lawrence Phillips, an optometrist at For Eyes in Cambridge. It’s also important, Phillips said, to make sure lenses are fitted to the exact curvature of the eye: “A contact lens is not something that you just take off the shelf and put on. It has to be fitted and monitored.”

In general, optometrists say, contact lens wearers should be on the alert for three possible warning signs: Eyes that feel dry or gritty, eyes that look red or irritated, and vision that is not clear with contacts in place.

“Very few people have these complications,” Beyer said, “if they come in for an annual eye check and follow the correct hygiene procedures.”