The BALL REPORTS

News As I Like It, Not As You See It:

Progressive lenses provide better.....

.....vision than Bifocal lenses

April 22, 2008

 

TRIFOCAL 1.50 D

Only Progressive Lenses Offer Continuous And Comfortable Clear Vision

The smooth, continuous progression of power in a progressive lens provides an uninterrupted field of clear vision from distance, to intermediate, to near vision, while offering precise distance related support to the presbyopic eye's reduced accommodation. At virtually every point on the progressive lens, the eye finds the power in perfect agreement with the distance at which it is focusing. Progressive lenses also offer continuous perception of space. When an eye looks through a progressive lens, its perception of spatial relationships is uninterrupted. Changes of power are gradual and continuous in all directions with minimal distortion. The abrupt change of power in a bifocal lens creates completely divided fields of distance and near vision, with no specific correction for intermediate vision. The eye's accommodation experiences abrupt changes because the wearer must constantly choose between distance and near vision powers and switch from maximum to minimum amplitude of accommodation. For example, consider an eye focusing through a bifocal lens at an object moving towards it from a reasonable distance. The eye first uses the distance vision power, accommodating to its maximum amplitude to focus as the object draws within arm's length. The eye then switches to the near vision segment where it must totally relax its accommodation for intermediate viewing, before again increasing to its maximum amplitude of accommodation as the object draws even closer. In this example, the eye must twice vary its amplitude of accommodation 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. A bifocal also disrupts spatial relationships. Because it is essentially a two-piece lens, a bifocal splits and alters spatial relationships. Vertical and horizontal lines appear broken, and image displacement occurs when the eye crosses the segment line.

PROGRESSIVE 1.50 D

Only Progressive Lenses Provide Comfortable Intermediate Vision For All Additions

Because their continuous progression of power includes an area designed specifically for intermediate vision, progressive lenses offer clear vision at intermediate distances. Bifocals have no intermediate vision powers. In fact, the segment line creates a blurred and doubled image where the intermediate vision area would be located. Nevertheless, intermediate vision is possible in low addition bifocals, but it can be rather uncomfortable. The wearer must choose between: 1) lowering the head and gazing through the distance-vision power (above the segment line) while employing the maximum amplitude of accommodation; or 2) raising the head and looking through the near-vision power (below the segment line) while totally relaxing the accommodation. Progressive lenses continue to offer clear vision at intermediate distances in high additions . This becomes impossible for bifocals in high additions because the distance and near vision powers can no longer compensate for the lack of an intermediate-vision power. The distance vision power cannot be used because the eye's amplitude of accommodation is now too limited; the near vision power cannot be used because the add power is now too great to allow for intermediate distance focusing. The only solution for the high addition bifocal wearer is to move further away from or closer to an object. Though they offer a clear intermediate field of vision, trifocal lenses are not an optimal solution because they impose two power jumps over two segment lines.

 

Your humble Ace Reporter

Bob

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