Bifocals

Bifocals are eyeglasses whose corrective lenses each contain regions with two distinct optical powers.

Bifocals are most commonly prescribed to people with presbyopia who also require a correction for myopia, hypermetropia, and/or astigmatism.

Franklin's original bifocals were designed with the most convex lenses (for close viewing) in the lower half of the frame and the least convex lenses on the upper.

Up until the beginning of the 20th century two separate lenses were cut in half and combined together in the rim of the frame.

The mounting of two half lenses into a single frame led to a number of early complications and rendered such spectacles quite fragile.

A method for fusing the sections of the lenses together was developed by Louis de Wecker at the end of the 19th century and patented by Dr. John L. Borsch, Jr. in 1908.

Today most bifocals are created by molding a reading segment into a primary lens and are available with the reading segments in a variety of shapes and sizes.

The most popular is the 28 mm flat-top bifocal, also known as the straight-top or D segment 28 mm wide.

CR 39 Plastic D28 Straight Top is our standard bifocal type.

When ordering bifocals we need to know the Pd measurement and the height of the reading segment, this can be obtained by uploading your calibrated image and trying on your selected frame in our click and measure virtual mirror.

If no segment heights are stated on orders received by Budgetspex an average ht will be used.