Despite the introduction of silicone hydrogels in the 1990s, overall corneal infection risk has held steady over decades, Schein said, affecting about one in every 2,500 lens wearers.
But that risk is “at least 10-fold greater for those choosing to sleep with lenses in. So I discourage that practice whenever I can,” he added.
As to why the risk is greater, Schein cited a number of factors that “favor microbial [germ] growth” whenever the eyes are closed, including “microtrauma to the surface of the cornea,” a drop in tear production, and a rise in temperature and humidity.
Amy Watts, director of optometry and contact lens service, and director of the vision rehabilitation service at Massachusetts Eye and Ear in Boston, said corneal function also plays a role.
“Our cornea is the only part of the body that receives its oxygen from the atmosphere and not our blood supply,” she noted.
So, “when we close our eyes at night, we reduce the amount of oxygen to our cornea by cutting the corneas off from the oxygen-rich atmosphere,” Watts explained.
“Wearing a contact lens further reduces the oxygen while asleep, and may put us just past the tipping point for keeping our corneas in optimal condition to fight off microbes,” she said.
Another issue is that people who sleep with their lenses also tend to shower with them in place. And “tap water — just like water in lakes, pools, ponds, oceans — can have microbes that may cause a serious eye infection,” Watts said. “In extreme cases, these infections can cause a severe loss in vision.”
Both Watts and Schein said preventing corneal infection is best achieved by wearing single-day disposable lenses.
Schein said, “This approach also removes the need for solution use and, most importantly, obviates the need for a contact lens case, an important advantage, since contamination of the case is certainly a risk factor for infection. However, if the user tries to save money by not discarding the lens daily, then the safety advantage is entirely lost.”
Meanwhile, he advises any wearer who develops a painful red eye to remove their lenses and see an eye care specialist within 24 hours.
“Most emergency rooms are not equipped with eye specialists or the equipment — [such as a] slit lamp biomicroscope — necessary to distinguish a simple abrasion from an infection,” Schein cautioned. “Therefore, those who go to emergency departments initially should be seen in follow up as soon as possible by an eye care professional.”