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Progressive Addition Lenses 133

In a progressive lens, an uninterrupted series of horizontal curves link
distance vision zone, intermediate vision zone and near vision with no
visible separation. Lens power increases smoothly from distance vision
area at the top of the lens, through an intermediate vision area in the middle,
to the near vision area at the bottom of the lens. They provide convenience
of use with no prismatic image jump. The subject feels confidence in
negotiating stairs; gutters etc., besides progressive addition lenses are under
constant research and development, providing us a newer and better design
to adapt faster (Fig. 11.8).

Fig.11.8: Progressive lens design principle

ADVANTAGES OF PROGRESSIVE ADDITION LENSES

Most eyewear professionals are aware of the product benefits afforded by
the optical features of a progressive addition lens:

No Visible Segments

No line of demarcation provides more cosmetically appealing lenses with
continuous vision, free from visually distracting borders. The lens looks
like a single vision lens (Fig. 11.9).

Continuous Field of Clear Vision
Progressive addition lens offers a greater visual flexibility with
uninterrupted clear vision from distance to near. Single vision reading lens
offers a field of clear vision limited to the near area only, while the abrupt
change of power in a bifocal creates completely divided fields for distance
and near vision with no specific correction for intermediate vision. At
virtually every point in the progressive lens, the eye finds the power in the
perfect agreement with the distance at which it is focusing (Fig. 11.10).