Eyeglasses have become common only in the past 100 years (and arguably in the past 60 years, about since the time visits to eye doctors became common). While there have been jokes about "four eyes" not breeding, because they can't get dates, neither this theory nor the converse appear to have any correlation with actual breeding patterns. Do more kids today need glasses than 100 years ago? Than 500 years ago? Than 5000 years ago? An interesting question, but claims that the past 60-100 years of eyeglass wearing have caused some major change in genetics seems to be a stretch.
Another possibility is that a large population of those with corrected vision had their vision slowly degraded by the early applications of the correction. I have no experience with vision correction, but I know anecdotally that most people with corrected vision need their corrections strengthened throughout their lifetime. In reality, their sight problem may have stabilized (or even improved) very early on in the absence of treatment. Thus, our perception of what sight abilities the average person in the United States has might be artificially deflated by early and aggressive treatment. Imagine putting back braces on all children that exhibited minor scoliosis - and asking them to leave it there all their life. If this were common, we might be speaking about how back strength and lifting ability must not be what they used to be... ----- John Kozubik - john@kozubik.com - http://www.kozubik.com