What causes near-sightedness?
Recently, I have been doing a lot of research on near-sightedness and eye health in general. I came across something called the Bates method. Basically it asserts that you can improve eyesight with methods such as not wearing glasses or looking at the sun for a brief time. His theories were discredited and almost no eye doctor takes his methods seriously. However, there are thousands who claim to have had success with this methods and have improved their eyesight. I am near-sighted and am trying to figure out why. My father was near-sighted, so genetics could play a role, but I'm starting to think environment does as well. It has been suggested that reading too much or staring at something close up for long periods of time will make you near-sighted. This makes sense, as there has been an epidemic of near-sightedness in the last 100 years. My question is, why? I have heard eye doctors claim that genetics is the only role that comes into play. If that's true, why the epidemic? And why are certain races of people affected more than others, particularly across literate populations? On the other hand, if environment is the predominant role, why do most eye doctors claim that genetics is the only factor? Thanks in advance.
What causes myopia (nearsightedness)?
…so why does myopia keep getting worse even though eyeballs don’t keep getting bigger?Well, the eyeballs do keep getting bigger. More specifically, the axial length of the eyeball (the distance between the anterior and posterior poles of the eye) is what keeps increasing.At birth the axial length is about 17 mm (on average). By adulthood, it increases to 24 mm in people with normal vision. For myopes, it becomes longer than 24 mm and for hyperopes it remains shorter than 24 mm. Each mm of length corresponds to about 2.5 D of correction. So if your axial length is 26 mm, you need -5.0 D of correction.The axial length can be measured with very high precision (0.1 mm) using infrared laser. This is required for determining the power of intraocular lens needed after cataract surgery.Now, what makes the eyeball for some people grow to 25 or 26 mm instead of 24 mm. That is a harder question, but the latest research shows that lack of sun exposure during childhood and teen years is a major factor. See:The myopia boomQuote: “The leading hypothesis is that (sun) light stimulates the release of dopamine in the retina, and this neurotransmitter in turn blocks the elongation of the eye during development. “Myopia Causes - Is Your Child at Risk?Quote: “The researchers calculated a 2 percent drop in the risk of developing myopia for each additional hour children spend outdoors per week. "This is equivalent to an 18 percent reduction for every additional hour of exposure per day,"”
What was life like for people with poor eyesight during the pre-modern eras? Were there any odd solutions people devised prior to the invention of eyeglasses?
People tended to do, what their eyes would let them. Nearsighted people worked up close, “normals” or farsighted were hunters, looking at distance. Farsighted and Astigmatism people found that if they squinted hard, they could see better. Some found if they looked through a button hole, they could see better far away. Now days, we use that same technique in testing eyes; we refer to it as a “Pinhole” or “Multiple” pinhole. It tells us quickly if the persons’ poor vision is due to just the need for new glasses, or if something else is wrong. If you wear correction, remove it and look through a very small hole, just poke some holes in a piece of paper, if it’s not too big, or small, you can see clear at distance.Eskimos, accidentally invented the “Stenopaic Slit”. Which is just like squinting, which works without using your facial muscles causing fatigue. It’s basically like a long skinny pinhole, but works the same. They initially used them to protect from “snowblindness” but found out they could see better at distance by wearing them. Eskimos tend to be more nearsighted than the general population, so these “snowblindness” glasses also improved their distance vision.
If nearsightedness, farsightedness, and astigmatism are genetic, then how come they didn't disappear through evolution?
Evolution weeds out traits that hinder reproduction and survival (of traits). My first guess would be that some of these traits were insufficiently negative to necessitate the complete eradication of said traits from the gene pool. For example, you wouldn't encounter much risk being slightly astigmatic if you could still differentiate, say a cougar from a tree. Another point is that some of these traits manifest after our reproductive prime - far-sightedness usually manifests after the age of 40. By that time, the prehistoric humans would have had enough time to reproduce and raise their offspring. As such, death due to farsightedness (indirectly) would not have cost the human species that much.Then there's the issue of group selection. I'm quite sure it was covered by another answer.Finally, I contend that the conditions for these afflictions to become aggravated were not present in the past - hunter-gatherer societies did not read as much as we did (no books anyway), nor did that have to submit reports and the like. So perhaps these traits were not strained out of the genetic pool because they didn't really manifest until now.Just my two cents. Hope it helps.
Isn't being an atheist who believes in egalitarianism contradictory?
Great observation. That reason alone is why I know atheist and like minded people are misinformed, or not very good at reasonable thought. I have thought the same think myself about atheist/liberal arguments and just conclude they are blowing smoke and spreading propaganda.
Will myopia decrease if I stop wearing glasses?
If you stop wearing your glasses, your vision beyond 40cm will be blurred. That’s about it. Your myopia will not decrease.It might seem to decrease if your initial refraction was wrong and you were given overpowered/overcorrected glasses. But if the measurements are accurate then don’t expect anything to happen by not wearing your glasses.The natural history of myopia is that it slowly increases in childhood, with or without glasses wear, if the particular genes and environment of the person are conducive for that to happen. The myopia then stabilises in the late teens or early twenties, with or without glasses wear. We know this from decades of seeing and treating patients.Even if we suppose that not wearing glasses could have a beneficial effect, life would be tough with the blurred vision from -2.50D of myopia. For sure, if the myopia is -0.50D or so there is no real need to wear glasses, but once it goes above -1.00D lots of things become blurry. A person with -1.00D of myopia would generally need to wear glasses to obtain vision good enough to drive a car.Let’s just say there are many controversial areas/topics out there in the world - many things which people disagree on.
Were people with bad eyesight considered blind before the invention of glasses?
If their bad eyesight was due to a condition that could have been corrected with glasses (e.g. Simple myopia=near-sightedness , or hyperopia= farsighted, or astigmatism), then they would not have been blind, but would have been at a severe disadvantage as far as survival goes; that is a myopic individual would not have been able to see a dangerous condition until he was right upon it (or until it was right upon him, as the case may be). Farsighted individuals would usually be OK until their late 20-30s, but if we are talking pre-history, humans life expectancy wasn't that long, so far sightedness wouldn't have made as much of a difference. Once humans stated living together in groups and building dwellings, then nearsighted individuals could have had a role that didn't involve hunter-gathering, as they could have been good at recognizing and differentiating certain plant and seeds, making clothing/furs, as musicians, storytellers, oral historians, etc. So they might have had some value to group survival at that point in time.
It is a myth that birthmarks are where you were wounded when you died in a previous life. Based on your birthmarks, how do you think you died in a past life?
My birthmark is a very nice little square on the back of my right forefinger:So maybe I lived in a culture where a ring was worn there as a symbol of love, and I was grievously wounded in my love and have carried that wound with me into this life on my finger! :)When I was a cute li’l Catholic boy, my parents told me that the birthmark was put there by God to note that I was very special so He could pick me out easily when I went to heaven!MJM, who’s always wondered why God didn’t just get a better pair of glasses if He’s nearsighted…