This insult to the eye tissues can result in damage to the eye. While the lens is still removed, the cornea is observed with the keratometer and the curvature of the front of your eye is measured. The keratometer also helps evaluate the corne al surface for irregularities. Poor fitting lenses or lack of oxygen can cause changes in the shape of the cornea, resulting in a change in the fit of the lens. Replace worn out or damaged lenses.
Contact lenses have a limited useful life.
Disposable lenses generally last 4 to 20 days, frequent replacement lenses hold up for up to 4 months, sometimes longer. Standard soft lenses are good for 6-12 months. One material, GMMA, has been know to maintain its shape and optical characteristics for as long a two years. Rigid gas permeable lenses of low to mid range gas permeability last up to two years and those of higher 'dk' values may begin to decompose after less than a year. Of course lens care and handling play a very important role in how long your lenses can continue to safely provide good vision and eye health.