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Progressive Addition Lenses 139

Mono Design and Multidesign
In case of mono design progressive addition lens, a single design is used
for all addition powers, i.e. the position for the near vision does not change
with the change in near addition power causing difficulties while viewing
near objects as the wearer holds reading material closer to him with the
increase in his near addition power. Hence, it can never offer optimum
comfort to both emerging presbyopes and matured presbyopes, as their
needs are different.
In multidesign the position for near vision changes with the addition
power change, i.e., the near area goes up with the increase in the addition.
All the twelve additions from 0.75D to 3.50D have been studied separately
to define the ideal design for each stage of presbyopes.

Asymmetry and Symmetry Design

Fig. 11.16