(2) Extended Focus Lenses for Near Work
These lenses allow for a gradual reduction in power as one looks through
a higher point in the lens. There are thus no visible lines in the lens.
Through a lower point in the lens, they enable near vision at the normal
reading distance, whilst vision through the top of the lens enables
vision at intermediate distances i.e. at about 50 to 100 cm. These lenses
are relatively new and are ideal for VDU use.
(3) Bifocal Lenses
These types of lenses have been in use for many years. They are particularly
useful when there is a refractive error for distance vision as well. They
are also useful for those individuals who have normal distance vision
but do not wish to wear a half-eye frame. This will still enable them
to regularly shift their focus and see clearly in the distance. In those
cases where the lenses would mainly be used for close work, a wider reading
segment would be preferred.