Bifocal Lenses contain two different prescriptions in the same lens. The main purpose of glasses bifocals is to provide the optimal balance between distance vision and near vision focusing needs. Eyeglasses bifocal lenses are available with the reading segments in a number of shapes and widths including sunglasses bifocal options. The most popular reading bifocal is the Flat-Top (also known as straight-top or D-segment), 28 millimeters wide. Eyeglass Lens Direct offers a number of options for the eyeglasses bifocal lens wearer.
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 D-segment, 28 mm wide. While the D-segment bifocal offers superior optics, an increasing number of people opt for progressive bifocal lenses.