People should avoid wearing contact lenses for more than eight or 10 hours straight, the Food and Drug Administration (FDA) said yesterday.
The agency posted an article on its Web site to answer a frequently asked question about whether contact lenses can be worn for more than eight hours a day.
The cornea has no blood vessels, so it gets oxygen from the air after dissolving it in tears, it said.
However, oxygen permeability is significantly reduced when a contact lens covers the cornea, it said, adding that the effects of reduced oxygen on the corneal surface include tearing, red streaks in the whites of the eyes, corneal bedewing and infection.
Wearing contact lenses for more than 10 hours can result in less oxygen reaching the corneal surface, but does not necessary lead to acute keratitis, the agency said.
However, if people often wear them for long hours, they might develop severe corneal hypoxia or corneal neovascularization — abnormal blood vessel growth in the cornea, it added.
Corneal neovascularization can also lead to corneal bedewing, permanent vision damage and even blindness, it said.
Tri-Service General Hospital Ophthalmology Department director Lu Da-wen (呂大文) said that many people have come to believe from experience that contact lenses should not be worn for more than eight hours, and the longer the lenses are worn, the longer the eyes suffer from corneal hypoxia.
There are two main types of contact lens material: hydrogel and silicone hydrogel, the most popular being hydrogel, because it is more comfortable, he said.
However, hydrogel is less permeable, so it is recommended that people wear them no more than eight hours at a time, he added.
The FDA urged people to wear contact lenses according to their doctor’s instructions and to only purchase lenses from certified brands and from sellers with a pharmaceutical dealer’s permit to ensure their quality.
Contact lenses should always be removed before going to bed, and people should immediately remove them and seek medical attention if they experience irritation or pain, it added.
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