THOSE MIRACULOUS PINHOLE GLASSES
How pinholes function. Pinhole glasses (also known as stenopeic glasses from the Greek words for "little opening") are not made of glass at all but of an opaque substance such as metal or plastic. The user looks through any of the many small holes in the material. These holes have the effect of reducing the width of the bundle of diverging rays (called a "pencil of light") coming from each point on the viewed object. Normally, the full opening of the pupil admits light. It is the improper bending of the outermost rays in that pencil of light which causes refractive errors such as myopia, hyperopia (farsightedness), presbyopia (diminished focusing range with age) and astigmatism to be noticeable. Pinholes can bring about clearer vision in all these conditions. By blocking these peripheral rays, and only letting into the eye those rays which pass through the central portion of the pupil, any refractive error in the lens or cornea is not noticed as much. The pupil may be wide open, but only the central portion is receiving light. The improvement in visual acuity can be striking.
Fig. 1 shows an eye with a pinhole lens in front of it. You will see that the eye does not need to deal with the rays that would need the most bending since they are blocked by the lens. It is said that Scheiner first described this effect in 1573. Those who are familiar with cameras will recognize that this is the same principle used to increase the depth of focus by decreasing the aperture. Pinhole cameras also operate by this principle.
An easy way to demonstrate this is to make a fist and put it up to one eye while closing the other eye. Open the fist just enough to create a small hole to look through. If you have a refractive error, you should see clearer this way. This same improvement in the vision takes place when someone squints to see more clearly. The upper and lower eyelids cut off the rays that would normally enter the top and bottom of the pupil and the vision improves somewhat. Since there is no similar way to cut off rays entering the sides of the pupil, these rays still contribute to the blurred vision. Looking through pinhole glasses instead of squinting cuts off the peripheral rays from all sides. Since the glasses are so close to the eye, the material between the holes is greatly out of focus and is not as disturbing as one might think. After a period of getting used to the glasses, the brain tends to ignore the presence of the material.
Also of interest is that the farther away the viewed object is, the less the pinholes are noticed. The honeycomb effect of the holes is more noticeable when viewing a book held close to the eyes, because the eyes are focused just a short distance in front of the glasses. When looking at a distant TV, however, the holes are hardly visible at all since the eyes are focused much farther away. Also, because of the distance, you can view the entire TV screen through one hole, an obvious benefit.
Looking through the teeth of a comb held in front of the eyes is another way to simulate the pinhole effect. The native people of Alaska have long used this principle by wearing glasses with narrow slits to look through, thus blocking out much of the glare from the sunshine reflecting off the snow and ice. Anyone who remains in this environment for long periods during the summer without protection can suffer from snow blindness. This painful condition forces the person to discontinue the use of the eyes until healing can take place. This is nature's way of protecting the eyes from permanent damage.
Some advantages that pinholes have over prescription glasses.
Using pinholes as sunglasses. A serious limitation of ordinary sunglasses that is not obvious to the average user is that they degrade the vision in two ways. The obvious way is that they reduce the amount of light entering the eye, making everything darker and harder to see. The less obvious way is that any refractive error (nearsightedness, farsightedness, astigmatism) is made worse. This happens because the pupil becomes wider to compensate for the loss of light when the glasses are put on. And the wider the pupil, the more any refractive error contributes to poor vision. This is a simple thing for anyone to verify. Of course, one answer to this problem is to buy expensive prescription sunglasses. And new glasses must be purchased whenever there is a substantial change in the vision.
Conventional, hole-type pinhole glasses also reduce the brightness of the sun, just like sunglasses. But they do so by creating a smaller pupil which improves the vision. This is also a simple thing to verify. Just put on a pair of pinholes on a sunny day and see how the brightness of the sun is reduced. One drawback of this solution is that the glasses have no ultraviolet protection.
But the most extraordinary use of pinholes in place of ordinary sunglasses is with the new smooth-lens pinholes. In addition to the light reduction that is provided by the small holes, the lenses have built-in UV protection. So you get a sunglass effect and better vision at the same time with no need for expensive prescription sunglasses. Smooth-lens pinholes are really the ultimate in eyewear. They are inexpensive, stylish, improve visual acuity, function as sunglasses, can be used indoors or outdoors, and can last a lifetime.
Using pinholes as computer glasses. Many people experience eye strain from using a computer for long periods. This has been given the name Computer Vision Syndrome and consists of such problems as fatigue, headache, dry eyes, eyestrain, blurred vision and double vision.
This has been attributed to glare from overhead lights, glare from the screen, poor contrast, reflections, poor lighting, squinting, infrequent blinking resulting in dry eyes, focusing close for long periods of time, ultraviolet light or "radiation" from the screen, inadequate screen resolution, etc. Also, letters on a computer screen consist of round pixels of light that form letters which are not sharply defined on the edges, different from the solid lines of normal print. This can create difficulty for the brain to accurately control focusing effort, resulting in blurred vision. The eye can tend to constantly shift its focus from the print to a point farther away and back again, causing fatigue. Various types of tinted glasses in various powers have been offered for sale to reduce the discomfort of computer work, but they often do not live up to their promises. Usually, the glasses seem to help for a while but then the old symptoms reappear.
However, many computer users do need a pair of glasses for their computer work that is different from the glasses they use for their other common visual needs. In other cases, they may have a vision disorder that would not otherwise require correction if they weren't performing a demanding visual job such as at the computer. Even people with excellent unaided vision could need glasses just for computer use. These are called "computer glasses".
It would seem that pinhole glasses offer as good a solution to this problem as it is possible to find, and at a much lower cost than other options. Glare from above or the sides is reduced by looking through the holes. The depth of field increases. Also, the focusing effort, or accommodation, is reduced, just as if you put on a weak pair of reading glasses. This also reduces the possibility of developing myopia from the constant close work, in those who are prone to do so. Ultraviolet, or other forms of radiation, have been shown to be of no consequence.
Myopia prevention. This brings us to a very important use for pinholes, Myopia Prevention, an application that has until now been totally ignored. When a person's eye has become abnormally long due to excessive close work, the outermost rays come to a focus in front of the retina and cause the blurred vision. Imagine for a moment the common situation where a child begins to develop myopia and can't see the board in school clearly. The usual solution of giving the child minus lenses is disastrous.
But suppose the child has a pair of pinholes and puts them on just to look at the board. A large area of the board can be seen through just one hole. The cost and the risk involved with minus lenses has been avoided entirely. Suppose the child also leaves them on when reading or looking at a computer screen. This could help greatly in preventing myopia since the accommodative effort is reduced. For those children whose natural farsightedness has diminished to around +0.5 diopters and are on the verge of moving into myopia, sitting down at the school desk and putting on the pinholes should be almost simultaneous events. Many children might need nothing more than this to insure that they do not develop myopia. Schoolteachers should have several pairs on hand to lend to the students who have difficulty seeing the board.
Limitations. One limitation of pinhole glasses is that blocking some of the light makes it more important than usual to have good lighting on the viewed object, even though the sharper image greatly compensates for the diminished light. When looking at television this is not a problem since the set makes its own light. When reading, a good lamp should be provided nearby. Another limitation is that peripheral vision is diminished, so they should not be used for driving or similar activities involving motion. As with any glasses, even sunglasses, they should not be used to stare at the sun, thinking that no harm can be done.
Pinholes cannot replace prescription glasses in every situation. People with over 6 diopters of myopia will probably not find pinholes useful, because pinholes cannot eliminate all of the blur. And just as it would be risky to wear ordinary glasses in situations where they could be broken and damage the eyes, there are situations where using pinholes instead of prescription glasses is not advisable. Use common sense and only wear the pinholes when the limited view does not pose a risk.
One group that should not use pinholes, or any glasses that reduce accommodation (focusing effort), is young people who are very farsighted. These people need to accommodate as much as possible in order to reduce their farsightedness to a lower level. This is nature's dynamic method of refining visual acuity in the growing youngster and it should not be defeated.
Opposition. Can you imagine what the eye doctors and optical industry think about this inexpensive solution? The fact that you don't find pinholes in the optical stores and eye doctors don't recommend them should give you a hint. In fact, it is just this opposition that has resulted in government persecution of those who sold such glasses in the past.
In the past, people who attempted to sell pinholes have left themselves open to this kind of attack by claiming that pinholes can permanently eliminate all kinds of visual problems. Such claims could not be substantiated. In one case, 14 state attorneys got together to close down one such operation that was advertising that pinholes could improve vision. How often do you hear of that many state attorneys getting together to do anything? The recent case where a lawsuit was brought against the tobacco companies is one of the few instances. That might be understandable since tobacco is an extremely harmful product that was costing the states hundreds of millions of dollars in health care costs.
But pinhole glasses are a perfectly harmless device, even if exaggerated claims were being made. Exaggerated claims seem to be the rule in the marketing world. What would create such a massive coordinated attack against a small company selling such a harmless product? Do you smell the presence of the eye doctors and optical companies in the background? Proof is difficult to find, but what other explanation is there? If there was a way to make squinting illegal, they would try to do it. Isn't it strange that pinholes are not offered for sale in retail stores, where they could be made available without making any claims at all for them, just like off-the-rack reading glasses? The reason is that any attempt to mass distribute them has been deliberately and massively squashed. The Internet has now made it possible to purchase pinholes without the eye doctors being able to stop it.