The grades for proper contact lens hygiene are in, and it’s sadly F’s across the board.

According to a new report released Thursday by the Centers for Disease Control and Prevention, a whopping 99 percent of wearers have engaged in at least one “contact lens hygiene risk behavior” known to increase the chances of developing eye infection or inflammation. And nearly one-third have had to visit a doctor because of eye redness or pain caused by their contact lenses.

Relying on market research, the CDC authors estimated that there are approximately 40.9 million Americans over the age of 18 who regularly use contact lens, 93 percent of which use soft contact lenses as opposed to rigid lenses.

A separate online survey of 1,000 contact lens wearers found that more than half of these wearers have even slept with them on overnight (50.2 percent); taken a nap with them on (87.1 percent); or simply added more disinfecting solution into their case as opposed to cleaning them out first (55.1 percent). 49.9 percent of wearers have kept their current lenses past the recommended date instead of replacing them; 82.3 percent have done the same for their case; 35.5 percent have rinsed their lenses under the kitchen tap, and 16.8 percent have actually stored their lenses in tap water. The list goes on and on.

While many of these faux pas may not dramatically raise the chances of infection or inflammation (several brands of contact lenses are designed to be worn overnight), taken as a whole, the CDC report highlights a glaring gap in contact lens safety.

“Of particular concern, contact lens wearers of all types frequently reported exposure of their contact lenses to water, including storing or rinsing their lenses in tap water and showering or swimming while wearing lenses. Exposure of lenses to water raises the risk for infection because microorganisms living in water can be transferred to the eye,” the authors wrote. “Even household tap water, although treated to be safe for drinking, is not sterile and contains microorganisms that can contaminate lens cases and contact lenses and cause eye infections.”

One of these microorganisms specifically noted by the report is the amoeba Acanthamoeba, which has been linked to several multistate outbreaks of serious eye infections among contact lens wearers in the past decade.

Altogether, there are nearly one million health care visits related to keratitis (cornea inflammation) or other “contact lens complications” annually, with a hefty medical bill of $175 million, according to the CDC.

“Prevention efforts could include vigorous health promotion activities that encourage contact lens wearers to improve their hygiene behaviors, such as keeping all water away from contact lenses, discarding used disinfecting solution from the case and cleaning with fresh solution each day, and replacing their contact lens case every three months,” the authors offered as recommendations to curtail these bad habits.

Source: Cope J, Collier S, Rao M, et al. Contact Lens Wearer Demographics and Risk Behaviors for Contact Lens-Related Eye Infections — United States, 2014. MMWR. 2015.