(4) Multifocal or
Progressive Powered Lenses.
These lenses allow for clear vision between
the chosen near distance all the way out to far
distances. This is made possible by the design of
these lenses. The power of the lenses gradually
reduces from the bottom of the lens (reading
portion) to the top of the lens (distance part).
There are thus no visible lines and unlike
bifocals, the wearer can achieve clear vision for
intermediate distances as well. This is useful
for a variety of everyday tasks such as reading
the price of goods at the supermarket etc.
These lenses are particularly useful for those
people who need to wear their glasses for quite a
few hours during the day and have varied tasks e.g.
the housewife who has difficulties with distance
vision as well as near vision. As multifocal
lenses usually have a relatively small reading
portion, they are not as suitable as single
vision lenses for extended close work or reading
in bed etc. Extended focus near lenses (see above)
are more suitable than multifocal lenses for VDU
The wearer is usually able to
adjust to multifocal lenses within the period of
one month if the glasses are worn on a rather
constant basis. Constant wear is recommended
initially until the wearer adjusts to the glasses.
The usual difficulties at first are a mild "swimming"
effect when walking and blurred vision to the
sides when reading. For closer work, the wearer
is advised to make more
head movements when looking to the sides so that
the eyes are constantly looking through the
centre of the lenses.