Lens Molding

Lens Fitting Of All Designs Of Bifocal Spectacles

In the current market of bifocal reading glasses, there are many unique lens designs using reading segments, in addition to the original design called Franklin bifocal. All forms of bifocal spectacles come with a power for presbyopia correction and another for nearsightedness or hyperopia. This is the functional common point among all lens designs. Over the years, bifocal reading glasses have helped a great number of presbyopic patients who still require a correction for an earlier gained problem like myopia or hyperopia. Behind this functional common point, there are actually different designs, which are closely associated with the methods of fitting of the lenses.

Most people know that a Franklin bifocal lens has a lower half section for near vision and another half for myopia or hyperopia. These two parts of different powers are noticeably separated by a line which goes all the way across the whole lens. This design may suggest that it is easy to mold those different powers. It is true when it comes to Franklin style bifocal spectacles. However, the task of lens fitting or manufacturing is no longer so easy when the target is a pair of bifocal reading glasses with molded reading segment. Nowadays, there are some basic lens designs using added reading segments. For instance, a D-shaped reading segment can be molded into a primary lens for presbyopia correction. And a round-shaped segment is also feasible. Another typical design is to use a narrow rectangular or a ribbon segment.

These designs require a precise fitting of the reading segments, which should be placed so the lines should rest at the same height as the wearer’s lower eyelid. Only in this way can his or her eyes be able to seek out the near-vision portion by dropping down slightly. Lens fitting of bifocal spectacles is considerably different from that of trifocals. A typical trifocal lens will be fitted a bit higher, with the top line of the intermediate area placed even with the pupil.

C: Bifocal spectacles including Franklin ones and other variations require the separating line to rest at the same height as the wearer’s lower eyelid, while a trifocal lens places its top line of the intermediate area even with the pupil.

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