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Different Kinds of Progressive Bifocals

Bifocals are eyeglasses with multiple sections. One section, usually the top, corrects distance vision. Another section of the lens, usually the bottom, corrects close vision. In older style bifocal lenses, the parts of the lenses were clearly visible with a line between them. Modern lens technology, however, has erased the line and given people more focal points in between the close focal points and distance focal points.

  1. Multifocals

    • Progressive lenses can take the place of both bifocal and trifocal lenses. Progressive lenses change the focal point of the lens gradually and over a smooth range. Instead of a jump from distance to reading, as happens with lined bifocals, progressive lenses let the wearer find a comfortable reading position. Although this is a positive point of progressive bifocals, the down side of the progressive lens design is a loss of peripheral vision in near-vision areas.

    Soft Design

    • Soft design is one of the two ways of making progressive bifocals. Soft design offers a wider field of view through intermediate distances. It also cuts down on the fuzzy area to the sides of the field of view. It offers the best quality of vision through the close and midranges, but has a slightly narrower field of view in the full bifocal area of the lens. It also can have a little more aberration at the lower part of the distance portion of the lens, near the transition to the bifocal portion. Soft design is best for frames that are at least 27 millimeters from top to bottom.

    Hard/Short-Corridor Design

    • The hard-corridor design, sometimes called the short-corridor design, suits smaller frames. The field of view for the middle-vision ranges is much narrower than that of the full bifocal portion and distance portion of the lens. The area of blurry vision to the sides of the lens at middle distances is larger than in soft-design lenses. Because of this narrow field of view, a wearer may have to move his head when reading wide computer monitors. One major advantage is this lens design has virtually no distortion, or aberration, in the distance-vision portion of the lens.

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