For any given substance, the heat capacity of a body is directly proportional to the amount of substance it contains (measured in terms of mass or moles or volume). Doubling the amount of substance in a body doubles its heat capacity, etc.
Conventional soft contacts can last up to a year; conventional rigid gas permeable (RGP) contact lenses can last even longer. Frequent or planned replacement contact lenses last one to several months. Disposable contacts last from one day (daily wear) to up to two weeks (extended wear).
State board recommendations vary between different states, but generally glasses prescriptions are only valid for two years, and contact lens prescriptions are typically only valid for 1 year (some states may vary). Even those who feel that nothing has changed should have regular check ups.