These Sunglasses Are Harmful

In every summer season we see the pharmacies in all parts of the globe filled with a strange assortment of dark spectacles, advertised as protecting the eyes and resting them. And you find people on their summer holidays, many of them wearing spectacles of this kind — gray, green, or brown — taking their sun baths in perfect confidence, indeed gazing into the hot glare of the sun. But it must not be forgotten that some of these spectacles do not give the protection and rest advertised. In truth, some of these spectacles injure the eyes to a great degree. Before we go deeper into this discussion, we must point out a self-evident truth: sunglasses that protect and benefit the eyes cannot be sold for a few piasters, because genuine sunglasses that protect and benefit the eyes are a purely technical piece of work.

A ray of sunlight does not consist only of heat and light. Besides the light rays which the eye sees, there are the infrared rays, which the nerves of the body feel, and likewise the ultraviolet rays; neither of these two kinds of rays can be seen. It is clear that any piece of smoked or ordinarily tinted glass — such as is used in cheap sunglasses — softens the simple rays, but does not filter out the invisible rays. And here lies the danger. Ordinarily the eye protects itself against the sun's glare by means of its natural structure, for the iris of the eye works like the shutter of a camera and narrows the pupil so as to admit a quantity of light sufficient to give a clear image on the retina; and it likewise reduces the heat rays and the ultraviolet rays that can enter the eye. But when you wear dark-colored spectacles, the iris does not work in the foregoing way — that is, it does not act like a camera shutter; on the contrary, it actually opens wider than usual in order to let in more light, and if these spectacles are not technically made, the way lies open for an unusual and injurious quantity of ultraviolet and infrared rays to enter. In this case there may result a swelling of the eyes, or the passage of the long ultraviolet rays through the iris of the eye or the eye's transparent covering, so that the natural lens of the eye is affected and becomes inflamed and watery, impairing its normal sight. And it is not the ultraviolet rays but the infrared rays that do the eye permanent harm. If you look up at the sun and then turn away from it, you see a dark patch for a short space of time. The reason is that the infrared rays have inflamed the retina with their scorching heat — that curtain standing at the back of the eye upon which the images of things are reflected. If you stare fixedly at the sun for a long time, this inflammation of the retina becomes serious to the point of permanently disfiguring the surface retinal tissues, and the dark patch appears in everything you see for the whole of your life. In fact, you become blind in a part of your eye. Some people think that cheap black spectacles will protect them from the danger of lying with their eyes open toward the sun, and perhaps this is the reason these spectacles are dangerous: for instead of protecting the eye, they help the harmful hot rays to settle upon the eye.

Accordingly, spectacles meant to absorb the ultraviolet and infrared rays and the colors of light that make up the sun's white light must be made according to the scientific principles of lens-grinding, so as to absorb the harmful rays before they reach the eye. There are spectacles that contain a thin filtering film between the layers of the two lenses, but since these spectacles are flat, they may reflect certain quantities of light back to the eyes and so tire them. In fact, a good pair of sunglasses must have two curved lenses.

There is another question, and we mean by it the color of the spectacles. The answer is that color is unimportant except in one respect: the effect of the color of the lenses on the colors you see. In countries that use the color system to direct the flow of traffic, it is best for sunglasses to be of a green color inclining to yellow, for this color causes no confusion in the colors seen, whereas spectacles of a dark amber color make the wearer unable to distinguish between red and green; and since red in traffic means stop and green means go, you may appreciate the extent of the harm that would result, not only to the flow of traffic, but to the driver of a car, if he used such spectacles.