I got my first pair of glasses in kindergarten. Everybody in my class wanted to try them on.
By the time I was 10 my vision was 20/200, which made my classmates even more eager to try on my glasses: seeing the world through my thick lenses was a mind-blowing experience, and, hey, it was the ’60s.
I’ve gone from glass lenses to plastic lenses to, finally, contacts. That means my personal “vision quest” has paralleled the development of eyeglasses…which makes it rather astonishing I’m only now writing about them. Maybe I’ve just been too close to the subject.
Portraits from the Middle Ages show people wearing eyeglasses, but the demand for them didn’t really take off until Gutenberg invented his printing press in the 15th century. Today, half the population wears eyeglasses to correct one (or sometimes two) of four focusing problems: myopia, hyperopia, presbyopia and astigmatism.
Myopia is nearsightedness, the inability to focus on distant objects. I can’t focus on anything more than five centimetres from my eyes. That’s because the light reflected from distant objects, after passing through my eye’s lens, focuses too far in front of my retina. (This is usually caused by an elongated eyeball.) A concave eyeglass lens, thinner at its centre than at its edge, pushes the focal point back.
Hyperopia, less common, is farsightedness, the inability to focus on nearby objects. In this case, the focal point of light entering the eye is actually behind the retina. A convex eyeglass lens, thicker at the center than at the edge, moves the focal point forward.
Presbyopia is the loss of ability to focus on very close objects caused by the stiffening of the eye’s internal lens after age 40. Almost everyone is subject to this, and those who are already myopic usually end up wearing bifocals.
The first bifocals were ground for Benjamin Franklin about 1760. The upper part of bifocals provides clear distant vision, while the lower part provides clear close-up vision. Today progressive lenses are available which eliminate the sharp line between the two areas, providing a continuous range of clear vision from top to bottom.
Astigmatism results from an irregularity of the cornea that blurs vision in one direction. To correct it, a cylindrical element must be added to the eyeglass lens, with the axis of the cylinder carefully aligned to correct the distortion.
For centuries, eyeglasses were made only out of glass. Glass provides sharp images, but it also has sharp edges when it shatters. (My father once got glass splinters in his eye when something hit him in the face and smashed his glasses.) As well, people like me require sharply curved lenses to correct their vision, which means the lenses have to be very thick…and very heavy.
In the last few decades, however, plastic lenses have increasingly replaced glass, today accounting for three-quarters of the market. Most are made from a resin called CR-39 that weighs half as much as glass.
High-index plastic bends light more sharply than CR-39, so lenses made from it can be another 30 percent thinner. This is great for very nearsighted people.
Lenses made from polycarbonate can be almost as thin as those made from high-index plastic–and polycarbonate, used in police visors and space helmets, is practically bullet-proof. It scratches rather easily, but anti-scratch coatings are available.
Whether glass or plastic, all eyeglasses fall off, frost up, get dirty, get lost and slide down your nose when you’re hot. Seven years ago, I switched to contacts.
Because they’re right on top of the eye’s own lens, contacts don’t have to bend light as much as eyeglass lenses and therefore don’t have to be very thick. The first crude contact lenses were made in the 19th century. They covered almost the entire surface of the eye; this prevented the movement of tears over the eyeball, requiring the frequent use of an artificial tear solution.
Plastic contacts appeared in the 1930s, and by the late 1940s, contacts were made that covered only the cornea. They floated on the eye’s own natural layer of tears, but they didn’t address another problem: the cornea, which has no blood vessels, obtains its oxygen directly from the air. Contacts cut off that oxygen, making the eye very uncomfortable.
In 1971, the soft lens, made of a gelatin-like plastic that soaks up water, was introduced. Some soft lenses today are as much as 80 percent water. This makes them gentle to the eye–unlike rigid lenses, which may take days, weeks, or forever to get used to–and enables them to transmit more oxygen to the cornea. Today, more than 75 percent of the people who wear contacts wear soft lenses.
However, because soft lenses mold themselves to the surface of the eye, they’re very poor at correcting astigmatism, caused by a distortion in cornea’s shape. For that you need a rigid lens, and in 1978 an improved rigid lens appeared, made of a new kind of plastic that was very good at transmitting oxygen to the eye.
Rigid gas-permeable lenses (which is what I wear) are easier to clean than soft lenses and last longer. Studies have also shown that soft lenses are more conducive to causing eye irritation (which can lead to infection) than gas-permeable lenses (probably because soft lenses are harder to keep clean).
A few years ago makers touted extended-wear contacts, but research indicated that people who wore them for days on end were highly susceptible to corneal irritation and infection. Most doctors now recommend wearing extended-wear contacts for no more than seven days at a time, and ideally taking them out every night. This gives them little advantage over ordinary lenses, so they haven’t proved very popular.
Contacts aren’t for everyone. Eyeglass wearers outnumber contact-lens wearers around four to one, and the ratio isn’t changing–for every person who begins using contacts, one user of contacts returns to glasses.
Not me. I wore glasses for more than 20 years, during which time I lost them (once in the Atlantic Ocean), broke them, scratched them and cursed them. Today I only wear them long enough to get from my bedroom to the bathroom to put on my contacts in the morning, and vice versa in the evening.
And you know what I like best about contacts?
Nobody every asks you if they can try them on.
