In optometry, "Continuous Wear" of contact lenses is a term used to refer to FDA approval of a contact lenses for wear continuously up to 30 days, then removing them for at least a full night of rest. "Extended Wear" lenses are approved for wear by the FDA for up to two weeks. And "Daily Wear" are not approved for wear while sleeping. Lenses that are approved for continuous wear or extended wear have high silicon content for increased oxygen transmission to the eye.
There is an increased risk of eye infections, corneal hypoxia and other conditions when the lenses are not removed for a night of rest, which can lead to permanent vision loss or even blindness. Also, different people have different risks for infection and hypoxia. Your eye doctor can determine if you've been experiencing corneal hypoxia with your lenses wear by the growth of blood vessels within the eye. If that growth goes out of control, it could lead to blindness. Paradoxically, one of the reasons for giving a lenses wearer directions for "extended wear" is because they have poor hygiene. This could be because of lack of motivation, disability, or the environment, for example an occupation that makes taking the lenses out and handling them a hazard. An eye doctor will weigh the risks of wearing lenses, and also the risks of daily wear vs extended wear and continuous wear. I've worn continuous wear with good results, by the way.
Contact lenses are also marketed as being disposable, Single Day Lenses, Two Week Lenses, 30 Day Lenses. The lenses that are to be disposed of frequently are made of a delicate material. Sometimes, for instance with Silicone Hydrogel 30 day lenses, the material is durable, but prone to deposit buildup that cannot be removed.
Although Silicon transmits oxygen well, it attracts protein deposits that reduce comfort and vision, and can potentially incubate dangerous pathogens. When pathogens build up a colony on a lens, they become more resilient to disinfecting solutions.
Although you may be able to wear a lens longer than directed, it may be increasing the hazards of lens wear exponentially as time goes by without disposing of them. It's less common to have a lens prescribed today, without directions to dispose of them after a set time. However, Rigid Gas Permeable lenses (Hard Contacts) are frequently used a year or two before disposal. However, RGP lenses are more durable, and they are hydrophobic and do not absorb solutions that might be tainted with pathogens. RGP lenses are the safest contact lenses and offer unsurpassed vision correction, especially for those with irregular corneas or irregular astigmatism, and they are offered as Daily, Extended and Continuous Wear. However, they are not normally prescribed to patients except in cases where a "soft" contact does not provide adequate vision correction, or if a patient specifically request to be fitted in RGP lenses. That is because they require a 2 month break in period before lens awareness disappears and the cornea and eyelids adapt.
I've worn several varieties of Soft, including Daily, Extended Wear and Continuous wear. And I've worn a couple for different material RGP lenses, which I currently wear as Daily Wear. They offer me superior vision correction. And with lenses staying crystal clean, I also find them more comfortable that the prior Soft lenses, but that was only after 2 months of adjusting to them. And, they are more affordable in the long run because the lenses should last at least a year, with good care. The downside was the adjustment period, and that take them out each night to clean and "condition" them in "wetting" solution. I would recommended you give them a try if you find that soft contacts do not correct your vision adequately, or if you are extra concerned with eye infection.