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152 Ophthalmic Lenses

Fig. 11.30: Skewed distortion in a progressive lens

2. Restricted Visual Field

Progressive addition lens restricts our field of vision particularly for
intermediate or near areas. The curves are always on the front side of the
conventional progressive addition lenses which position the visual area of
the lens at considerably away from the eye. The ultimate result is restriction
of visual field.

3. Compromised Optics

Conventional progressive addition lenses are produced in varying base
curves averaged for a wide range of prescription and a nearest suitable
front base curve is used for a given prescription. Ideally the base curve
selected should match the exact curves used on the backside. This is simply
not possible in conventional progressive addition lenses. As a result acuity
is compromised to some extent in all visual areas, depending on how close
the front base curve is averaged for the patients prescription.

4. No Control over the Inset of the Near Portion

Some progressive addition lens designs do have an inset, which varies with
addition and/or distance correction, but not yet with interpupillary
distance.

5. Difficult to check with Focimeters

Progressive addition lenses are relatively difficult to check with the help of
focimeter, specially if the original engravings including those indicating
distance power circle and near power zone cannot be found.

REMARKING PROGRESSIVE ADDITION LENSES
Majority of the progressive addition lens manufacturers employ laser etched
molds or fluorescent markings on the front lens surface to help dispenser