Confused about contacts? Advances in contact lens technologies have created many
options in addition to hard and soft lenses. Today, contact lenses are likely
to be described in one or several of the following ways.
By their prescribed wearing period: The time that the lenses are left in the
eyes.
- Daily Wear (Up to 18 hours)
- Extended Wear (For overnight use, up to seven days)
By their replacement schedule: The time interval for replacing lenses.
- Planned - (Frequent replacement: 1 month, 1-2 weeks; daily disposable)
- Unplanned, or Conventional Replacement - (No specific time schedule before
lenses are replaced)
By the type of vision correction for which they are designed:
- Spherical (For near- or farsightedness -- myopia or hypermetropia)
- Toric (For astigmatism)
- Bifocals (For presbyopia)
By the type of tint they have:
- Tinted to improve handling only
- Tinted to enhance your eye color (For light-color eyes)
- Tinted to change your eye color (Opaque tints for light or dark eyes)
- Clear - without tints
Of course, contact lenses are also still described by the basic type of material
of which they are made.
- Soft (hydrophilic)
- Rigid Gas Permeable
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.
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
(hypermetropia);
- Toric contact lenses for astigmatism;
- Bifocal lenses for 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 one eye is fitted with a distance lens and
the other with a reading lens. Approximately two-thirds of patients adapt to
this type of contact lens wear.
By Type of Tint
Contact lenses may be described as clear or tinted. Tints are used to make lenses
more visible during handling, or for therapeutic or cosmetic reasons. Tints can
enhance eye color, or change it altogether.
Three categories of tinted contact lenses are available.
- Cosmetic enhancement tints are translucent and are designed to enhance your
natural eye color. They are best for light-colored eyes (blues, greens, light
hazel or grays). When wearing these tints, the color of your eye is a blend
of the lens tint and your natural eye color and iris pattern.
- Opaque or "cosmetic" tints change the color of your eyes whether they are
dark or light. The pattern on the lens, which is colored, overlies the colored
part of your eye, resulting in a color with a natural look.
- Visibility tints are very pale, colored just enough to make the contact
lens visible while you are handling it. They usually have no effect on eye
color.
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