There are two categories of contact lenses based on recommended wearing time:

• Daily wear contact lenses — These must be removed nightly before sleep.

• Extended wear contact lenses — These can be worn overnight (for a limited number of days).

"Continuous wear" is a term that's sometimes used to describe extended wear lenses that are worn 24 hours per day for up to 30 consecutive days.

When to replace your contact 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.