When I was in high school years ago (shortly after getting my new glasses) I thought a disproportionate amount of the student population required prescription lenses. I had always figured that the percentage of people that required corrective lenses in any given population would be rather small (say, 10-15 percent). I later became shocked when, as I became more social, I learned that a huge amount of people wore contacts.
I just came from a small get together with some friends of a friend. Everyone but one person wore glasses, and for all I know she had contacts. This little subject started to burn through my mind, so now here I am…
What’s going on? I always thought “20/20” was ‘normal.’ If so many young people require prescription lenses…is there something odd going on? Or is 20/20 not normal but a higher standard than usual?
Cecil speculates that poor vision is a product of civilization. I figured this might be a factor. Is there any evidence that reading actually leads to myopia, far-sightedness, astigmatism, etc.? Is 20/20 ‘normal’? If we went back thousands of years or even to caveman times would most of our ancestors have ‘normal’ vision? Or would a similar percentage need correction? I’m guessing that may be unknowable, but hey, I’m on a roll.
This page says that the percentage for corrective lenses is similar between the U.S. and some third world countries, but cites diseases, poor nutrition, etc. for the third world. That is certainly understandable, but then wouldn’t they have a higher percentage? What explains the U.S. percentages then?
It’s a conspiracy by the lense manufacturers I tells ya!
First of all, I’m not any kind of eye doctor; I’m basing this on my own observation and logic.
First of all, it really is possible to if not “ruin,” to impair your eyes through excessive close work. The focusing muscles need exercise, too, and if you (like me) mostly have your nose in a book or at a computer monitor, you risk not doing enough far vision focusing. Sort of like if you only used one hand and never used the other, the muscles in the un-used hand would not be as strong.
Secondly, after about 40 or so, it simply becomes harder for the eyes to focus as well as they used to, and most people become more farsighted, or at least have some difficulty with near vision.
Third, in a non-literate society, the emphasis would not be on close vision for most people, so the eye would get lots and lots of far vision development.
Finally, in ages past, I think greater variation from average would be more tolerated than now. Since we have the capability to correct our vision, most of us want to be as near to optimal as we can.
Well, I agree with your first sentence, but then you lose me. Leading ophthalmologists agree that you cannot impair your vision by reading too much or working at a computer monitor or sticking your nose in a book. Your second, third and fourth points are relatively accurate, however.
Many are myopic (near-sighted) and my take on this is this is a development that allows people to read when they get older without corrective lenses. If you are only slightly myopic, when you do get presbyopia (which is the loss of the ability of the lens and its ligamentic attachments to allow close focus), you will be able to read and see close up. However, if you have 20/20 vision, you will need corrective lenses to see close up once you pass age 40 or so. So possibly this was a development in mankind to be slightly myopic. Evolution does not always produce perfection, and many become too myopic. However, it does not explain farsightedness.
Evolution ain’t perfect. Survival of the fittest and all that. You’d think that those so myopic would’ve been weeded out of the gene pool. Perhaps myopia came later.
Not necessarily. Sub-optimal vision is sub-optimal for modern tasks such as reading, watching TV, and typing - for hunter-gatherer activities, it might be a hindrance, but not necessarily a fatal one, particularly in co-operative societies.
I’d imagine that unless vision was impaired to the point of near-blindness, it wouldn’t confer a deadly disadvantage for early man - my eyesight is shot to hell, but I don’t doff my hat to lamp-posts or mistake libraries for movie theatres - or sabre-tooth tigers for rocks, for that matter.
I suspect there’s also the matter of life-expectancy: since severe shortsightedness is mostly exarcerbated by age, with a shorter life-span most early humans would probably have been dead before it became an issue.
Besides, there may well have been a selective advantage to myopia: while the tough hairy he-men with 20/20 vision were out harrying the woolly denizens, who do you think was taking advantage of their eyesight to hop on with the womenfolk? The short-sighted, that’s who: “Sorry, Ugg, damn eyes are playing up again. You and Ogg go and hunt mammoths, and I’ll, uh, stay here and help the girls weave baskets. Yeah, baskets. Great Spirit, but I wish I could go hunting with you guys. Mind out for the sabre-tooths, now.”
{Anyone more knowlegeable about opthalmology, palaeontology or anthropology is welcome to come along and shoot holes in my reasoning. Except the last paragraph: that’s my fantasy, and I’m sticking to it.}