The early 1700s saw the emergence of daily newspapers for the man on his way to work, or sitting in the coffee house.  Just as now, a significant percentage of the population suffered with imperfect sight.  Spectacles and magnifiers of all sorts had been available for two centuries, but it was the advent of the newspaper which saw them really take off.  Spectacle-makers produced huge ranges of tortoiseshell, horn and whalebone (super-flexible and hard to break) as well as silver.  They could be purchased off-the-shelf with the prescription or 'focus' written on the arm, or made-to-measure.  Edward Scarlett of Soho (1730) was the most famous of the early makers, with his spectacles being marketed as having 'the Exactest way of fitting different Eyes'.  He also introduced arms to spectacles (usually of the pince-nez type before) and catered for different activities such as reading or sewing.

The bifocal lens was invented in the 1760s, but by whom it is impossible to say.  Benjamin Franklin is commonly cited as the culprit, but that's most likely just a nice myth.  They were first used for artists who could look at their subject through the top and their canvas through the bottom, but they soon became common amongst clerks, academics and scholars who didn't want to be putting them on and off all the time.  

Later on in the century, green and blue lenses started to appear.  The idea came from Venice, where they were apparently used to deflect the sun reflecting from the lagoon, but the Venetians were expert glass-workers and it is quite possible they already had a medical use.  In England they were quite possibly used as filter for dyslexia sufferers, as they are often seen in lenses with a 'reading focus'.  

To get fitted for spectacles, it was usual to go to one of the many little 'Optickal' shops in and around Soho and the City.  There spectacles could be tried out, and fashionable frames chosen.  The widespread availability of spectacles and their common use is clear by the inventory of Nathaniel Adams of Charing Cross in 1741: he died with 499 pairs of ready-made spectacles in stock, ranging from the cheapest horn frames at little more than a few pence, to silver ones at a shilling each.  Of all of the shops in Georgian London, I would love to get a peep inside Scarlett's emporium (or Adams's, who was Scarlett's apprentice).

These spectacles from my cabinet of curiosities are silver, which is handy because it means we can tell when and where they were made: they are hallmarked for London, 1791.  They're hinged halfway down each arm, making them foldable, comfortable to wear and surprisingly they are very light.  The cases were often shagreen or leather and deliberately slim to keep them pocket or reticule friendly.  I'd have had some horn ones with the blue lenses and a stained shagreen case, or maybe the silver ones with the gr....