What are they?

BiFocals are eyeglass lenses with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism.

What’s their history?

Original bifocals were designed with convex lenses (for close viewing) in the lower part of the frame and the least convex lenses (made for seeing objects that are far away) on the upper half of the lens. Up until the start of the 20th century, two separate lenses were cut in half and then jointed in the rim of the frame. The mounting of two half lenses into a single frame led to a number of early complications and left such lenses extremely fragile. A methodical way for fusing the sections of the lenses together was developed by Louis de Wecker, at the end of the 19th century, and then patented by 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.

What are they?

Progressive lenses, also called multifocal lenses, or BiFocals with no line in the middle, are corrective lenses used in eyeglasses to correct presbyopia and other disorders of accommodation. They are characterised by a gradient of increasing lens power, added to the wearer’s correction for the other refractive errors. The gradient starts at the wearer’s distance prescription at the top of the lens and reaches a maximum addition power, or the full reading addition, at the bottom of the lens.

What’s their history?

The first patent for a PAL was British Patent 15,735, granted to Owen Aves with a 1907 priority date. This patent included the manufacturing process and design which was however never commercialized.

The Carl Zeiss AG & Varilux lenses were the first PAL of modern design. Bernard Maitenaz, patented Varilux in 1953, and the product was introduced in 1959 by Société des Lunetiers (now Essilor). The first Varilux lenses’ surface structure was however still close to a bifocal lens, with an upper, aberration-free half of the surface for far vision and a rather large “segment” for clear near vision. The breakthrough in user adaptation and comfort, as well as peripheral and dynamic vision however occurred in 1972 with the introduction of Varilux 2, for which Maitenaz created a totally aspheric design and manufacturing process. Carl Zeiss AG developed freeform technology in 1983 with its own patented progressive series Gradal HS.

What are they?

Trifocals are eyeglasses with lenses that have three regions which correct for distance, intermediate, and near vision.

What’s their history?

John Isaac Hawkins developed the trifocal lens in 1827. Trifocals are mostly used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition. Trifocals are mostly used by people with advanced presbyopia who have been prescribed 2 diopters or more of reading addition.