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Extended wear or continuous wear contact lenses are lenses that
are worn overnight for continuous periods, normally of one to
four weeks. Most extended wear lenses are worn continuously
for up to a week. What distinguishes these lenses from other
lenses is their high oxygen permeability.
What are the types of extended wear contact lenses?
Extended wear lenses have higher water content than other types
of contact lenses. They are therefore classified according to
their water content. They are classified into the following three
types.
- Higher water content lenses with water content of 70%
to 80%. These lenses have the highest oxygen permeability but
are less resistant to deposits and therefore get easily damaged.
- Medium
water content lenses with water content of 48% to 69%. These
lenses are often the first choice in extended wear lenses.
- Low
water content lenses with water content of 38% to 45%. These
are thin lenses and sometimes difficult to handle.
When are they used?
Extended wears contact lenses are favored by people who want
to avoid the hassle of frequent removal or wearing of lenses.
Such people could include those with naturally poor vision who
are greatly handicapped without lenses or glasses. Groping in
the night would be a big problem for them. They are also used
by people, whose natural vision is not so poor, but prefer the
convenience of extended wears. Extended wears are also used for
cosmetic reasons.
What are the advantages of extended wear contacts?
- Due to higher water content these lenses more easily
conform to the shape of the cornea.
- They have very high, almost
6 times oxygen permeability than other contacts. Given all things
equal, chances of eye infections
are less with these lenses.
- Extended wears are very convenient especially for
those with poor vision. This great convenience can be enjoyed
by people
who don’t
want to handle lenses frequently.
What are the disadvantages of extended wears?
The convenience of extended wears comes with the inconvenience
of more complications. The ideal extended wears must strike a
balance between the convenience needs of the users and the safety
needs demanded by practioners.
Some common complications are discomfort, dryness and dry eyes.
These problems occur with other lenses also but their incidence
is five times higher in extended contacts.
The reasons are obvious. Which are prolonged continuous wear,
especially overnight wear, infrequent cleaning and reduced oxygen
supply for long periods due to the cover provided by the lenses.
Some organisms lodged under the lenses survive better in such
conditions.
Initially they were approved for continuous wear up to two weeks.
Approval for 30-day wear came shortly afterwards. But due to increasing
complications, the approval was reduced to a week. Some practitioners
went further and discouraged their patients from sleeping with
extended contacts. The number of extended wear contact wearers
went down.
Worn as they are, such complications with extended wears are
unavoidable. Even the best of materials with the highest possible
oxygen permeability will not be rid of these problems. At best
the complications may be reduced.
What are the latest developments?
Disposable extended wears where the lenses are replaced every
six or seven days were shown to be safer. These lenses reported
fewer complications. A significant development was that fewer
people discontinued extended wears. But disposable contacts did
not lead to reduction in corneal ulcer cases.
Extended wears made from silicon hydrogel were introduced next.
These lenses allow six times higher oxygen in to the cornea. In
silicon-hydrogel lenses, higher water content increases oxygen
permeability. The reverse is true in conventional soft contacts;
higher water content causes lower permeability. Some practitioners
began approving some brands, made from silicon hydrogel, for 30-day
wear. Disposables were making a comeback.
To make these lenses safer still, improved lens designs and better
cleaners and disinfectants are also being introduced.
What should I do to make extended wear safer?
- Avoid smoke and swimming with lenses
- Avoid sleeping with lenses
if it is not too inconvenient
- Immediately see a doctor if you
have red or irritated eyes, reduced vision or any other discomfort
- Follow
your doctor’s instructions faithfully
Conclusion
Extended wear contact lenses offer great benefits. But they come
with more complications. These are unavoidable but can be reduced.
Improved materials, lens design and cleaners are being introduced.
Meanwhile, you must strictly follow the doctor’s instructions
about safety, usage and cleaning procedures.
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