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Advantages and use
• The additional lens power required for clear vision at
different viewing distances is accounted for by the
natural position of the eye during the majority of day
to day tasks, and can be further adjusted by tilting the
head to sight through the appropriate part of the
vertical progression;
• The lens location of the correct addition power for
the viewing distance usually only requires small
adjustments to head position, since near vision tasks
such as reading are usually low in the visual field and
distant objects higher in the visual field.
• Progressive addition lenses avoid the discontinuities
(image-jumps) in the visual field created by the
majority of bifocal and trifocal lenses and are more
cosmetically attractive. Since bifocal and related
designs are associated with 'old age', proponents have
suggested the lack of segments on the lens surface of a
progressive lens appears more 'youthful' since the
single vision lenses associated with younger wearers are
free of segments or lines on the surface.
• Progressive lenses can use the optimization principle,
which is based on linearization and represents the lens
surface using special spline functions. The lens’ power
progressively increases between the high-power and
low-power region of the lens. This specialized lens
surface provides an accurate power distribution for both
near and distant vision and reduces the number of
optical aberrations. |
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With many advantages, it
has some disadvantages - peripheral distortion, need adaptation etc.
To overcome all this fitting PALs needs an adequate and skilful
person.
With the advancement of new technologies and different lifestyle,
demand of vision clarity and comfortibility has increased.
Therefore, PALs provide basic hard design, soft design, advanced
soft design and upto personalized design.
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