Editing Bifocals (section)

== Construction ==
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 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 John Louis Borsch Jr. (1873–1929)<ref>{{Cite journal |last=Ravin |first=James G. |date=November 2009 |title=The multifaceted career of Louis Borsch |url=https://pubmed.ncbi.nlm.nih.gov/19901225/ |journal=Archives of Ophthalmology  |volume=127 |issue=11 |pages=1534–1537 |doi=10.1001/archophthalmol.2009.264 |issn=1538-3601 |pmid=19901225}}</ref> in 1908. In 1915, Henri (Henry) A. Courmettes (1884-1969), a French immigrant to the US, patented the “Flat Top” (or “D Segment”) reading portion of the bifocal.<ref>{{cite web | url=https://patents.google.com/patent/US1160383A/en? | title=Bifocal lens and method for making the same }}</ref> The advantages were wide reading area, less prismatic effects and no image jump between distance and close viewing.  This was first introduced in mass production by the Univis Lens Co. of Dayton, OH. in 1926.<ref>{{cite web | url=https://entokey.com/prescribing-multifocal-lenses/ | title=Prescribing Multifocal Lenses | date=10 July 2016 }}</ref>  In 1935, Courmettes went on to patent the Tilted Bifocal Lens,<ref>{{cite web | url=https://patents.google.com/patent/US1991544A/en? | title=Bifocal lens }}</ref> in 1936, a method of grinding two prescriptions simultaneously on that Tilted Bifocal Lens,<ref>{{cite web | url=https://patents.google.com/patent/US2040242A/en? | title=Method and means for surfacing solid bifocal lenses }}</ref> and in 1951, the Cataract Bifocal Lens.<ref>{{cite web | url=https://patents.google.com/patent/US2574960A/en? | title=Cataract bifocal lens }}</ref> 

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