What are Varifocal Glasses?

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what are varifocal glasses ?
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Varifocal glasses, also known as the progressive
glasses, graduated glasses and no-lines bifocals
are generally used to correct presbyopia and have
become one of the most used glasses for
prescription as well as designer glasses. The
name comes from the fact that the glasses have
different power at different levels of the lens.
At the top of the lens, the power is minimum,
which gradually increases in the middle level and
finally, the bottom part of the lens has the
maximum power.
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It is widely regarded, that the worlds first
commercially available varifocal glasses was
developed by Duke Elder in 1922 and was
subsequently sold by Gowlland of Montreal. In
1953, Bernand Maitenaz developed the first modern
varifocal lens The Varilux, which was introduced
by the Société des Lunetiers (which later became
a part of Essilor).
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The greatest advantage of varifocal glasses is
the ability to look at objects at varying
distances with just a slight tilt of head. As the
different levels have different powers, the top
part can be used to view objects at a distance,
the middle one at the objects at an intermediate
distance and the bottom part while working on
nearby objects, like reading a book. They also
avoid the discontinuities like image - jumps
which occur in the visual fields created by
bifocal and trifocal glasses. Commercially,
varifocal glasses are quite popular too, because
of the absence of any line on the lens.
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The primary problem with the varifocal lens is
its requirement of a careful placement which is
related to the users pupil centre to generate a
distance viewing reference position. Incorrect
specification of this location can cause serious
problems which include narrow fields of vision or
even clear vision in only one eye. The need to
adapt to uncomfortable head positions may also
arise, which is unhealthy and risky to the entire
body.
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Finally, it takes time to adjust to varifocal
lens. It may range from few hours to almost two
weeks. During this adapting phase, side effects
generally include headaches and dizziness.
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