By Wearing Period
Daily Wear: Lenses prescribed for daily wear are to be worn only during waking hours, usually up to a maximum of 18 hours. Daily wear lenses are removed at night and cleaned and disinfected after each removal.

Extended Wear: Extended wear lenses may be worn on an overnight basis for up to seven consecutive days (six nights). You should wear your lenses on an extended wear basis only on the advice of your optometrist.

Extended wear lenses generally have a higher water content or thinner center thickness than other lenses and permit more oxygen to reach the eye. However, their use has been linked to a higher incidence of eye problems. Extended wear lenses need to be cleaned and disinfected at recommended intervals or discarded after use.

By Replacement Period
Contact lens are often prescribed with a specific replacement schedule suitable to your specific needs. Planned (or Frequent) Replacement contacts are disposed of and replaced with a new pair according to a planned schedule. Unplanned replacement lenses (often called conventional lenses) are not replaced according to a pre-determined schedule. They are typically used for as long as they remain undamaged, usually around 12 months for soft lenses.

Why replace lenses frequently?
Almost immediately after they are inserted, contact lenses begin attracting deposits of proteins and lipids. Accumulated deposits, even with routine lens care, begin to erode the performance of your contacts and create a situation that presents a greater risk to your eye health.

A specific replacement schedule helps to prevent problems before they might occur. Contact lens wearers, in turn, enjoy the added comfort, convenience and health benefits of a planned replacement program. Planned replacement lenses are generally a thinner design or are made of different, more fragile materials with a higher water content than unplanned replacement or conventional contact lenses.

Based on a complete assessment of your needs, a prescription for planned replacement lenses may call for replacement:

• Quarterly
• Monthly
• Every 1-2 weeks
• Daily
  

Except for daily disposables, planned replacement lenses require cleaning and disinfection after each period of wear unless they are discarded immediately upon removal. Planned replacement lenses can be worn as daily wear -- removed before sleep -- or as extended wear, if recommended by your practitioner.