Tech in Plain Sight: Goggles – Tips & Results

Eyeglass wearers, try a little experiment. Take off your glasses and look at this site or at least something you can’t see well without glasses. Now imagine that you lived in a time when nothing could be changed about your vision. If you wear contact lenses or see well – maybe you’ve had surgery – then congratulations. But for most of us, age-related vision changes are a fact of life. Many young people also need glasses or other measures to be able to see well. At first glance you might think that glasses are an obvious invention, but it turns out that we haven’t gotten real glasses in quite some time and modern glasses really are a piece of high tech that is – literally – right in front of your face hidden .

What is wrong?

Human eye with parts labeled
Parts of the eye (CC=BY-SA 3.0 by [Holly Fischer]

Before we talk about vision correction, it’s helpful to know what can go wrong with your eyes. To understand this, it helps to first examine how your eye works.

Light first enters the eye through the cornea, a clear dome at the front. The light then goes through the pupil, the black dot in the center. The colored part of your eye, the iris, controls how much light lets through, much like the aperture on a camera.

Inside your eye is a transparent lens structure that focuses the rays of light. They pass through a jelly-like substance that keeps your eye round, and the focus is on the retina, which contains light-sensitive nerves. Unlike a camera, the retina is not flat like a piece of film, but curved. However, as with any camera, the image is now upside down, but your brain doesn’t mind. That being said, if you flip your vision so that it’s really upside down, your brain will eventually dutifully flip it back for you, as you can see in the video below.

When things go wrong

People generally think of vision problems as farsightedness or nearsightedness. That is, blurred objects near or far. However, you can also have astigmatism, which just causes general blurring, and what we consider farsightedness can be caused by two distinct problems with your eye.

Astigmatism occurs when the shape of the cornea is not perfect, allowing incoming light to land on the retina in more than one place. When you have astigmatism, everything looks blurry and something like an LED appears to be more than one LED from afar.

Hyperopia, a type of long-sightedness, and myopia, or short-sightedness, occurs when the length of the eye is wrong or the lens system has the wrong focal length. In hyperopia, the image focuses behind the retina and myopia has the focus in front of the retina. The other cause of farsightedness is presbyopia, in which the center of the lens in the eye hardens as we age. The end effect is the same as with farsightedness, and that is why as we age we become unable to read the fine print.

The optics

Lens and prism diagram
You can think of a lens as two prisms, either base to base or tip to tip

You can think of a lens as two prisms. In a concave lens, the two prisms meet at their vertices. With a convex lens, they meet at the base. If you’re not used to thinking of a lens as a pair of prisms, you might like the following video.

As the video mentions, light bends around the base of a prism. Ok, it doesn’t really flex, but that’s a good way to think about it. So when light enters a concave lens it tends to spread out, but through a convex lens it tends to converge at a point some distance from the lens – the focal length.

This is at least true for a spherical lens. You can also have a cylindrical lens that focuses on a line instead of a point. If you need both types of lenses at the same time, you need to find a toric lens.

By spreading or converging the image before it hits your eye, glasses can correct common vision problems. You can also correct astigmatism with a cylindrical lens. Of course, if you have multiple problems, you need a toric lens.

Old story

While it may seem easy to create a lens and hang it in front of your face, there are two parts to it. First you need to know how to make a lens, or find one that occurs naturally. Next you need to have the idea of ​​how to hang them in front of your eyes.

Glass has been around for at least 4,000 years, but no high-quality glass. There are some claims of ancient lenses being used to either magnify the sun or focus it to start fires, but they are either natural stones or very poor quality glass and it is debatable whether they would have worked in both cases.

The Romans got good at making glass in the first century and realized that a bean-shaped piece of glass—a convex lens—would make objects appear larger. The word lens comes from the Latin word for lens.

However, the story is a bit vague about using lenses to help people see. It looks like an Arab created reading stones in the 900s and they became relatively common by the year 1,000. If you’ve ever used one of those solid plastic sticks that you attach to something small like a phone book to make the text bigger, it’s the same idea. Of course, the material would be glass or crystal.

glasses arrive

El Greco portrait showing a bespectacled cardinal
This portrait by El Greco from around 1600 shows Cardinal Fernando Niño de Guevara with glasses (public domain)

It was to be the 13th century before we started seeing what we would imagine to be simple glasses. Early glasses in Italy were roughly blown glass held in a frame of leather or wood. Until about 1600, however, the glasses were held in the hand or pressed on the nose. The early glasses were all convex, although concave lenses were known by 1400. It would be 1604 before Kepler explained why they all worked.

Around 1600 someone devised how to clip glasses to one’s ears, although this is often credited to Edward Scarlett in 1727. However, as you can see in the adjacent painting by El Greco, some people had this style of glasses as early as the 1600s.

Earbuds were a game changer, although you can still find the occasional monocle or pince-nez. There was another big problem: glasses powerful enough to see things up close would confuse things that were far away.

Benjamin Franklin, who had poor eyesight, invented the bifocal lens, in which each lens had a near part and a far part. There have been some claims that Franklin did not invent them but popularized them. It would not be until 1825 that astronomer George Airy figured out how to correct astigmatism.

Modern glasses

Like everything else, eyewear became high-tech at an accelerating rate throughout the 20th century. Frames are now made with memory alloys that return to their original shape. Lenses made of special material are lightweight and durable. They may also have coatings to reduce glare, block UV light, or go dark in bright light.

One of the biggest improvements came from bifocals. First there were trifocals with three lenses. However, sophisticated lens grinding techniques now allow for progressive lenses, where the lens has different properties that change continuously across the lens.

Computers can grind lenses into classic shapes or create aspheric or atoric lenses that can correct vision in more sophisticated ways than a normal lens. In the following video you can see the process of a typical glasses laboratory.

RX and other solutions

Knowing Latin helps if you want to read an eyeglass prescription. You see numbers under the heading OS and OD and rarely OU0. The O stands for Oculus (eye), the S for Sinister (left) and D for Dextrus (right). The U means both eyes.

If you don’t have astigmatism, you’ll see diopter numbers for each eye. This is the amount of focus change you need, and lower numbers are better (a diopter is the reciprocal of focal length in meters). A negative number means you are nearsighted and a positive means farsighted. A zero would mean you don’t need glasses, so you probably won’t see this unless you just have a bad eye.

For astigmatism you will see three numbers. The first is the diopter, the same as above, and is called the SPHERE. The next number is a measure in diopters of how much astigmatism needs to be corrected (CYLINDER). The last number is the axis between 0 and 180 degrees that gives you the rotation of the correction.

If you need bifocals or varifocals, you’ll also see an ADD number. These are the extra diopters needed for bifocals. In the case of a progressive lens, there is of course a continuous increase in magnification across the lens. This number is almost always the same for both eyes but if one of them has PAL next to it then it should be used for both eyes with progressive lenses and the other number is for proper bifocals. Sometimes you will see a PD or pupillary distance. This is used to set up the frame, but has no effect on the optics.

One might think that with contact lenses and laser vision correction surgery, glasses would not be very common. But they are. Why not? They are relatively cheap, require little maintenance and work well. While the technology that goes into them today requires computer-controlled grinders and a lot of math, even the simple glasses that were available centuries ago must have worked wonders for people who could no longer read or see clearly.

It’s possible to build your own lenses, but it’s hard to match the quality of a real lab. Glasses used to be nerdy, now they’re fashionable. If you want to look like a nerd again and need progressives, you might prefer a pair of these.

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