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(A)Presbyopia
For those people who are affected by
presbyopia or "old"-sightedness, there
are several designs of lens that can be used,
depending on various factors such as the demands
of the work task and whether there is an
associated problem for distance vision as well.
(1)Single
Vision Lenses for Near Work.
- Normal full-sized frames can be used with
single-powered lenses. When the
presbyopia is advanced, this will give
clear vision only at the particular
distance that is chosen at the time of
the examination. When the presbyopia is
at its early stages (up to about fifty
years of age), there is a greater range
of clear vision. Single vision
spectacles should be removed prior to
looking away as they blur distance vision.
They may cause a quicker deterioration of
near vision if, for the sake of
convenience, they are not removed when
watching TV etc.
- To overcome the problem of distance blur when wearing single
vision near glasses, half-eye frames ("look-overs")
can be used if there is negligible refractive error for distance
vision. This has a few important advantages over the use of full-sized
frames for reading. Most importantly, one has the freedom to look
away onto a distant object without experiencing blurred vision.
This not only offers the convenience of not having to remove one's
glasses but also encourages long-term eye health. Probably
the most important visual hygiene measure is the regular shifting
of the focus away from the near task and onto a distant object.
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