Contact lenses are a viable option for active people, athletes, and those who prefer the freedom from eyeglasses. Your doctor of optometry has the training and qualifications to specify the proper lens material, fitting design, and care regime that will work best for your eye condition and lifestyle. Contact lenses are generally described by their wearing period, replacement schedule, correction style or tint.
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 doctor of optometry. 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 and discarded after the predetermined use period.
By replacement period
Contact lenses are often prescribed with a specific replacement suited to your needs and the design of the contact lenses.
- Planned (or frequent) replacement contacts are disposed of and replaced with a new pair according to a planned schedule, usually daily, biweekly or monthly.
- Unplanned replacement lenses (often called conventional lenses) are not replaced according to a predetermined schedule. They are typically used for as long as they remain undamaged, but should be replaced every 12 months. These lenses are used much less frequently and are usually reserved for special circumstances.
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 contact lenses 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 generally have a higher water content or thinner center thickness than other lenses and permit more oxygen to reach the eye. They are less protein and lipid resistant, and need to be replaced more frequently as they become dirty more easily. Based on a complete assessment of your needs, a prescription for planned replacement lenses may call for replacement:
- Every 1-2 weeks
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.
By type of vision correction required
Contact lenses may be identified by the type of refractive error they are designed to correct.
- Spherical contact lenses for nearsightedness (myopia) and farsightedness (hyperopia);
- Toric contact lenses for astigmatism; and
- Multifocal lensesfor presbyopia, the loss of ability to focus on reading or close-up activities.
As an alternative to special bifocal contact lenses, many practitioners use a system called monovision where the dominant eye is fitted with a distance lens and the non-dominant eye with a reading lens. Approximately two-thirds of patients adapt to this type of contact lens wear.
By type of tint or colour
Contact lenses may either be clear or tinted. Tints are used to make lenses more visible during handling, or for therapeutic or cosmetic reasons. Tints can also enhance eye colour, or change the eye colour altogether. Three categories of tinted contact lenses are available:
- Cosmetic enhancement tints are translucent and are designed to enhance your natural eye colour. They are best for light-coloured eyes (blues, greens, light hazel or grays). When wearing these tints, the colour of your eye becomes a blend of the lens tint and your natural eye colour and iris pattern.
- Opaque or cosmetic tints change the apparent colour of your eyes whether they are dark or light. The pattern on the lens, which is coloured, overlies the coloured part of your eye, resulting in an eye colour with a natural look.
- Visibility or handling tints are very pale, coloured just enough to make the contact lens visible while you are handling it. They usually have no effect on eye colour and are often a pale blue or green.