David King Dunaway

Later on in the 17th century, somebody came up with a way of creating wire frames, which would allow people to swap lenses as their visual needs changed.

That took place in Nuremberg, Germany, and its design and the idea of interchangeable lenses traveled well across the world.

Well, it's hard to know because in many parts of the world, it's very hard to get visual exams of any accuracy at all.

In the United States, we have something like 220 million people who wear glasses regularly.

In the world as a whole, it's probably somewhere between 4 and 5 billion people.

That's right.

And your friends who wear glasses with plain lenses are among the 16 million Americans who simply wear them as a fashion device or to change the way they will appear or to benefit from some of the positive stereotypes of glasses.

Well, the vision correction industry probably has its roots in that ancient peddler who wandered around with a box strapped to his neck.

As an industry though, it really takes off in the 18th, 19th century when the training for optometrists and opticians became more regularized.

Doctors have been working on eyes for

4,000 years, but the process of correcting vision is relatively new to the human species.

Well, part of that is because people are leading longer lives.

And for many people, the need for glasses appears in their 40s and 50s.

And that's called presbyopia.

And it's simply the result of people's eye muscles weakening and the lens itself losing its flexibility so that

In particular, close-up materials become hard to see.

I'm sure your listeners are very familiar with this process, and that's why we have reading glasses today.

To come back to an earlier point you made about what I call the selfies phenomenon,

As soon as glasses were invented, somebody else denounced them as diabolical.

The Church of the Middle Ages and even so-called Dark Ages resisted the use of glasses, saying, you should take the eyes that God gave you and not expect to improve them.