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Progressive Addition Lenses 135















                   Fig. 11.11: Extreme right picture shows clear intermediate vision through
                                         progressive lens
               through a bifocal lens at an object moving towards it from a reasonable
               distance. The eye first uses the distance power, accommodating to its
               maximum amplitude to focus as the object is drawn within arm’s length.
               The eye then switches to the near segment where it must totally relax its
               accommodation for intermediate viewing, before again increasing to its
               maximum amplitude of accommodation as the object is drawn closer. Thus,
               the eye varies its amplitude of accommodation twice from minimum to
               maximum. This adjustment in accommodation would occur only once with
               a progressive lens, just as it would with natural, non-presbyopic
               accommodation.

               Continuous Perception of Space

               Progressive lens also offers continuous perception of space. When an eye
               looks through a progressive lens, its perception of spatial relationship is
               uninterrupted. Changes of power are gradual and continuous in all
               direction with minimum distortion. Single vision reading lenses do not
               allow real spatial perception. The two portions of bifocal lenses split and
               alter spatial relationship. Vertical and horizontal lines appear broken and
               image jump hampers wearer’s vision (Fig. 11.11).



















                   Fig. 11.12: Perception of form and movement through a progressive lens
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