The Correction of Visual Problems
Posted by Cataracts - 31/05/09 at 06:05 pmThe strength of reading specs was originally based on the patient’s age. A middle aged man would be issued glasses with a strength of 2 degrees and a person of more advanced years offered a 4 degrees of strength pair of specs. It wasn’t until the middle of the 19th century that eyeglasses started to be issued by people who knew some basics about optics.
It’s crazy that in the 21st century, people still choose to pick out the most convenient set of reading glasses by trying them on at the local store.
Astigmatic correction was not generally available until late in the nineteenth century, despite Airy’s cylindrical correcting lens (1827) and Donders’ comprehensive book on refraction (1864). Many inventive solutions come out of necessity and it was the same for bifocal lenses. Bifocal lenses were actually invented by Benjamin Franklin. He needed some for himself and did a bit of a Heath Robinson Job, by cutting each of his lenses in half and sticking them together, so that he could see into the distance using the top half and read with the bottom half of his lenses.
In the early 1800s Hawkins tried to launch trifocal lenses to the spectacle wearing population. Successful multifocal lenses, which have smoothly increasing power over the lower half of the lens, with no visible segment line, were brought in during the 1960s. Unfortunately, these lenses are such a compromise in optical terms, and the field of clear vision in the reading area is so small that, for even the short lines of print when it is in double columns, the reader is obliged to turn his head slightly to follow along each line.
It may be that multifocal lenses do have a role in patients with emerging multifocal lenses, as they may be better positions to tolerate the increasing strengths.
You may find the history of specs interesting as I do. I would advise you to really study specs and their beginnings to help you better appreciate what a wonderful device they truly are. If you are intent on purchasing your specs online, then please make sure that you get them from a proplerly trained source.
