Contact lenses are designed to improve a person’s vision, but if not used properly they can also hurt your eyes.

A report released today by the Centers for Disease Control and Prevention (CDC) states that 1 in 5 eye infections related to contact lenses involve serious eye damage.

The figures were part of the CDC’s Morbidity and Mortality Weekly Report (MMWR).

The numbers were derived from the Food and Drug Administration’s (FDA) Medical Device Report Database.

The report was released in advance of Contact Lens Health Week next week.

“Contact lenses are a safe and effective form of vision correction when worn and cared for as recommended,” said Michael Beach, Ph.D., director of the CDC’s Healthy Water Program, in a news release. “However, improper wear and care of contact lenses can cause eye infections that sometimes lead to serious, long-term damage.”

Read more: Get the facts on eye emergencies »

Serious but preventable

For their report, CDC officials looked at 1,075 contact lens-related infections reported to the FDA between 2005 and 2015.

More than 10 percent of those cases involved a patient who went to the emergency department or urgent care clinic.

In all, about 20 percent of these reports involved people who suffered serious eye damage.

In the most extreme cases, patients had scarred corneas or suffered vision loss. Some needed corneal transplants.

CDC officials said 1 in 4 infections resulted from easily avoidable behaviors.

“Around 41 million people in the United States wear contact lenses and benefit from the improved vision and comfort they provide,” Dr. Jennifer Cope, M.P.H., medical epidemiologist in the CDC’s Waterborne Disease Prevention Branch, said in a news release. “While people who get serious eye infections represent a small percentage of those who wear contacts, they serve as a reminder for all contact lens wearers to take simple steps to prevent infections.”

Read more: Screen time hurts more than kids’ eyes »

Common mistakes

CDC officials said the most common mistakes are people sleeping while wearing contact lenses that are not designed for overnight use, as well as users not replacing lenses when they’ve hit their expiration date.

Dr. John Bartlett, an ophthalmologist at the Ronald Reagan UCLA Medical Center, said the most common problem they see is people wearing their contact lenses for too long.

He said many times contact lenses may still feel comfortable after their two-week or one-month recommended stint, so people continue to wear them.

Bartlett said contact lenses should be discarded when they expire regardless of how they feel. He added if the lenses don’t feel comfortable before that time limit, they should be tossed out early.

“Continuing to wear them puts you at greater risk,” he said.

Bartlett, however, said the most dangerous mistake people make is to “top off” solutions used to clean contact lenses.

He said leaving even a small amount of old solution in a lenses case and then putting in new solution can create problems. Among them is the fact the mixed solution can dilute the liquid’s ability to kill germs.

Bartlett recommended emptying any old solution and then letting the contact case dry before adding new solution. He added replacing the cases at least every few months is also a good idea.

Read more: Is chronic dry eye something to cry about? »

Recommended precautions

CDC officials listed three main recommendations for contact lenses users in their report.

The first is not to sleep with your contact lenses in. They said that can increase the risk of infection by 6 to 8 times.

They also agreed with Bartlett that contact lens solution should never be topped off. “Adding new solution to used solution can lower germ-killing power,” the report stated.

The third suggestion is to replace contact lenses as recommended by your eye doctor.

“People who do not replace their lenses as often as recommended have more complications and report more eye problems than those who follow the replacement recommendations,” the report stated.

In addition, the FDA has put out a cautionary recommendation for decorative contact lenses that can change people’s eye color. They suggest those accessories be obtained through a prescription just like other lenses.

Bartlett said consumer education is a key to reducing eye infections caused by contact lens misuse.

“There are many contact lenses users who are not aware of these recommendations,” he said.