Myopia, or nearsightedness, is extraordinarily common -- affecting as much as 50% of the population of the United States. Given the large number of people who need glasses or contact lenses to correct this refractive error, one might wonder how nearsighted people managed in the hundreds of thousands of years before spectacles were invented. From what is now known about myopia, most people's vision may have been considerably better in ancient times. The basis for this assertion is the surprising finding that the growth of the eyeball is strongly influenced by focused light falling on the retina. This phenomenon was first described in 1977 by Torsten Wiesel and Elio Raviola, who studied monkeys reared with their eyelids sutured closed. This procedure, obviously enough, deprives the eye of focused retinal images. Animals growing to maturity under these conditions show a remarkable elongation of the eyeball. The effect of this deprivation is a local one, since the abnormal growth of the eye occurs in experimental animals even if the optic nerve is cut. In fact, if only a portion of the retinal surface is deprived of focused light, then only that region of the eyeball grows abnormally.

Although the mechanism of light-mediated control of eye growth is not fully understood, many believe that some aspect of modern civilization -- perhaps reading and writing -- interferes with the normal feedback control of vision on eye development, leading to abnormal elongation of the eyeball. A corollary of this hypothesis is that if children wanted to improve their vision, they might be able to do so by practicing far vision to counterbalance the near work "overload". Practically, though, most people would probably choose wearing glasses or contacts rather than the onerous daily practice that would be required. Not everyone agrees that such a remedy would be effective, however, and some investigators and drug companies are exploring the possibility of pharmacological intervention during the period of childhood when abnormal eye growth is presumed to occur.

Neuroscience, Sinaur Associates (QP355.2.N487 1997)

Another widely held theory for the myopia epidemic is that the invention of corrective lenses effectively eliminated any evolutionary advantage in having decent eyesight, and coincidently, improperly shaped eyeballs are a tremendously dominant trait. Or in layman's terms, good eyesight is a particularly fragile aspect of the human genetic code. Thus, even in the short period of time involved, having made myopia a non-terminal, life-destroying condition has allowed it to proliferate naturally, effectively reversing genetic evolution.

For the quick to criticize, corrective lenses have been around for a (relatively) considerable amount of time. Anecdotally, the Roman tragedian Seneca, born in about 4 BC, is alleged to have read "all the books in Rome" by peering at them through a glass globe of water to produce magnification. Ground glass "Reading stones" (aka maginfying glasses) date back to roughly 1000 CE. The first recorded use of ground-lense eyewear seems to date to the latter half of the 13th century.

Why do so many people receive ever increasing eyeglass prescriptions? Perhaps it's due to repeated, technically accurate, lens prescriptions during childhood.

Different body parts grow and change at different rates, at different times. I suspect the resulting changes in visual acuity, if left alone or moderately corrected, would tend to self-correct over time, or, at least, they would usually not worsen at a rapid rate.

In my experience, optometric prescriptions are set to achieve the best possible vision under unrealistic test conditions.

The usual eye test is in a darkened room. The patient is shown a Snellen eye chart of letters, simulated to be about 20 feet away. Various lenses are selected for the patient to look through, using a phoropter machine. With each lens change there are questions such as, "Which looks better, this or that?"

This routine is used to determine an overall lens curvature, measured in diopters. Next, choices are made about relative astigmatism, which is a difference of focus in different radial planes. The measurement results in a cylinder of 0-180 degree of varying diopter strengths. If the idea of cylinder is not clear, imagine looking sideways through a perfectly clear glass cylinder rod, like a clear swizzle-stick, which stretches an image in one direction.

Another chart is presented at book-reading length to determine the ability of eyes to focus on things close.

The Snellen eye chart displays rows of letters of varying sizes, indicative of relative visual acuity. The 20/20 line indicates the ability to discern, at 20 feet, what the average person would see at 20 feet. There are other lines indicating superior than average acuity. Under the test conditions, you might be able to achieve better than 20/20, with the right lenses applied. Maybe you can get down to 20/15, or even 20/10, especially when the patient is trying very hard to stay focused; "Which is crisper, and more clear? Is it this, or that?"

Perhaps there are some problems with the optometric prescription process. I think there is some controversy about this.

The testing is done in a darkened room. Eyes naturally dilate in a darkened room. It is also possible a hurried optometrist applies eye-dilating drops in advance of the vision testing. They do that so they can easily examine the insides of the eyes, using a rather bright slit-lamp. One's pupils tend to constrict under bright light, and a dilated pupil makes it easy to get a good look inside.

Eyes focus more clearly when the pupils constrict, which is unlikely in a darkened room, possibly with drugs administered that prevent normal pupillary action. Constriction of the pupils creates a pinhole effect, making images sharper. Dilation makes images less sharp. Some may know the "blurry eyed feeling" coming away from the optometrist.

Testing in a darkened room with dilated pupils is quite different from average real life scenarios. I think all this means the testing is simply a non-realistic scenario.

If you're in a dark room and need to see, what's the first thing you do?

It's not unusual to hear people say they were prescribed a series of ever increasing eyeglass prescriptions. Over time, the eyes adjust to the lenses, rather than adjusting to the natural non-lens environment. I think repeated re-prescription for young people interferes with what would be a more natural growth process.

This might be interesting to parents with children.


(May tick off any one who practices this, or possibly add to their thoughtfulness.)

Go out on a sunny day, and see just as well, or better, than people who say they've been told, or decided, they do or don't need glasses.

Part of the point there, is that if you get the "extra perfect" prescription, tuned for a darkened room, and spend a lot of time out in broad sunlight, or reading material up close, then your eyes and body train to adjust for that, and that, I think, can lead to ever increasing prescriptions for young people when they, and their eyes, are still growing.

PS A little looking around turns up a lot of material that I think confirms at least one of my suspicions. Testing eyes focus in a darkened room, possibly with use of drugs that dilate the eye, does not result in a realistic best prescription.

The person with the major, -7+, coke bottle lenses was likely the geek whose parents were overly fussy, took them to the optometrist every year, and made sure they got into reading books all the time, using those lenses designed for the best possible acuity. The essence of this is simple, their eyes were trained into myopia, by the continuous prescription and application of lenses.

"Glasses" really are spectacles if you're Elton John.

If a child who is perhaps barely four years old, asks you this question, as you both sit in the eye doctor's waiting room, as you look with love at green eyes fringed with long lashes that when shopping women notice and shake their heads saying, "such a shame to waste long eyelashes on a boy," you politely ignore them.

You do not use large words like pediatric strabismus or blame it on genetics or heredity.

You tell the child who is perhaps barely four, that Mommy and Daddy both wear glasses, then you help them name every other person the child knows who wears glasses. You explain, "People wear glasses so they can see clearly all of the things they like to look at."

The child smiles, trusting you, and says, "like birds and fire trucks and horses and pictures in books?"

"Yes," you answer, hoping there will be no need for surgery and that it was caught in time so this green-eyed boy does not grow up almost legally blind, like two grandparents.

Log in or register to write something here or to contact authors.