Editing Contact lens (section)

===Replacement schedule===
Contact lenses are often categorized by their replacement schedule. Single use lenses (called 1-day or daily disposables) are discarded after one use. Because they do not have to stand up to the wear and tear of repeated uses, these lenses can be made thinner and lighter, greatly improving their comfort. Lenses replaced frequently gather fewer deposits of [[allergens]] and [[pathogen|germs]], making these lenses preferable for patients with ocular [[allergies]] or for those who are prone to infection. Single-use lenses are also useful for people who wear contact lenses infrequently, or when losing a lens is likely or not easily replaced (such as when on vacation). They are also considered useful for children because cleaning or disinfecting is not needed, leading to improved compliance.

Other disposable contact lenses are designed for replacement every two or four weeks. Quarterly or annual lenses, which used to be very common, are now much less so. Rigid gas permeable lenses are very durable and may last for several years without the need for replacement. PMMA hards were very durable and were commonly worn for 5 to 10 years but had several drawbacks.

Lenses with different replacement schedules can be made of the same material. Although the materials are alike, differences in the manufacturing processes determine if the resulting lens will be a "daily disposable" or one recommended for two- or four-week replacement. However, sometimes manufacturers use absolutely identical lenses and just repackage them with different labels.<ref>{{Cite news |date=1993-07-12 |title=The Only Difference Is When You Throw Them Away |url=https://www.bloomberg.com/news/articles/1993-07-11/the-only-difference-is-when-you-throw-them-away |access-date=2016-12-26 |work=Bloomberg.com}}</ref><ref>{{Cite web |title=Contact Lenses – Types of Contact Lenses. Disposable (Replacement Schedule) Contact Lenses |url=https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/HomeHealthandConsumer/ConsumerProducts/ContactLenses/ucm062319.htm#dcl |access-date=2016-12-26 |website=www.fda.gov |language=en}}</ref>