CONTACT LENS WEARING TIME
Until 1979, everyone who wore contact lenses removed and cleaned them nightly. The introduction of extended wear enabled wearers to sleep in their contacts. Now, two types of lenses are classified by wearing time:
Daily wear — must be removed nightly
Extended wear — can be worn overnight, usually for seven days consecutively without removal
"Continuous wear" is a term that's sometimes used to describe 30 consecutive nights of lens wear — the maximum wearing time approved by the FDA for certain brands of extended wear lenses.
Even with proper care, contact lenses, especially soft contacts should be replaced frequently to prevent the build-up of lens deposits and contamination that increase the risk of eye infections.
Soft lenses have these general classifications, based on how frequently they should be discarded:
Daily disposable lenses — Discard after a single day of wear
Disposable lenses — Discard every two weeks, or sooner
Frequent replacement lenses — Discard monthly or quarterly
Traditional (reusable) lenses — Discard every six months or longer
Gas permeable contact lenses are more resistant to lens deposits and don't need to be discarded as frequently as soft lenses. Often, GP lenses can last a year or longer before they need to be replaced.
The most frequently prescribed contact lens replacement schedule in the U.S. in 2017 was monthly (40 percent), followed by daily (35 percent), every one to two weeks (24 percent) and annually (1 percent).