Here's a good study:
http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1003299
It's a study on 45,000 caucasian people genetically. The results were that they identified genes that are implicated in the eventual need for glasses. Those children that had the "bad genes" in the 90th percentile (the worst) risk group (survival probability of surviving without need for any glasses) had a probability of ending out with no need for glasses of 40%. So what they're saying is that they identified genes or "risk alleles" that if you end up with those, you have a certain probability of NOT needing glasses (their survival probability if you carry those genes). Apparantly you can end up with risk alleleles and still not develop myopia. Also you can carry those genes and develop myopia. Also there is no analysis of two adults one with myopia or two with myopia. I think what they're saying is that if you inherit the bad genes you have a certain probability of ending out with no need for glasses. But the study outlines what they're saying and they do mention the fact that there has been an environmental hypothesis, but what they're looking at is risk alleleles on genes and what they seemed to have concluded is that whether you end up with glasses is based on what you inherited but also the survival probability among the entire group that all ended up with "risk alleles" with in the worst case a 40% chance of not needing glasses, and the process is linked to the very early growth of the brain, in particular the retinal cells. But to be analytical, they discovered that even among those who inherit the risk genes that they looked at in their study, you have a probability at worst case of 40% surviving without the need for glasses. And to repeat 60% of those who inherited the "bad genes" at worst case ended up with a need for glasses. And to add another loophole, they do no analysis on if a person with glasses mates with a person with no glasses, they only looked at the genes of the group and analyses. So in theory it may be likely that one person with glasses mating one person with not glasses the chances of a child not needing glasses is 80% among a random group of people, but probably amongst the whole more like 70% if one of them has glasses. ---So my take on this is that everybody inherits or ends up with two sets of genes, one selected from the mother and one selected from the father. The ones that end up with no need for glasses but perhaps had a myopic parent inherited "bad genes" but they ended up not being expressed perhaps recessive I'm not sure. Or on the flip side the ones that were expressed were the ones that did not need any need for glasses, but perhaps when THEY MATE [[my take on this is that those who have the risk alleleles and ended up with no need for glasses have the risk gene amongst their genes but the one that is expressed on that site came from the other parent who passed down a gene that was not a risk allele on that site]] are identified they still carry the risk for carrying on genes to a child that will perhaps statistically add a very slight increase in the need for glasses. Many large famillies have and still do not have any members going back 100 years with no need for glasses. Other areas, perhaps in asian cities, over 3 generations have built up a "weight of refractive propensity" that is expressed above 80% in that city. So the way I would look at it is where you are located and if not that many people have glasses and you have glasses, it doesn't seem to be any problem with mating with a large number of them and not really affecting future generations, because who knows in the future eyeglasses may be outlawed as a deterrent to natural selection. Labrador retrievers in some areas who keep over 100 of them, 30% end up with refractive errors, but they mate constantly, and there are progenators who are myopic, but it must balance out amongst the nattural selection on those estates to where only 30% need glasses, and it doesn't overwhelm the group even though you may have a progenator in one generation who is dominant and mates with all the female dogs, the probability is that the next generation the progenator is still one who is free of refractive errors, dominant, and mates with all the other dogs. And to further add a note in some studies myopia with greater than refraction -6 diopters has been discovered to be autosomal dominant. If say your parent was not high myopic but needed glasses and your other parent had no person in a large family going back generations with any need for glasses, then even though you have glasses the odds are that identifying those risk alleles that you do carry from the progenator, when YOU MATE the ones passed down to the offspring are statstically speaking going to de-select those "bad genes" since the one parent had no risk for myopia, but statistically, you in what you are looking through ended up with an eight ball, but the sheer probability is that the child will not need glasses especially if the one you mate does not need glasses since you have no autosomal dominant genes, you're just as likely to pass down the "good gene" from the non-progenator in your parents. So let's say that of 20 genes that contribute to myopia, you inherit ten of them and you cannot have more than 6 to develop myopia. And let's say that ideally two people without glasses the child has a 1 in 40 chance of needing glasses. To get 1 in 40 with two parents with no need for glasses, that would mean that one of the parents (not both) has a bad gene. So let's assume your partner has 2 bad gene out of the 40 genes they care considering they have 2 copies of genese one from each parent., and you have 10 bad genes out of 20 or really 20 out of 40. When these combine, just roughly speaking, you can simplify it to 10 out of 20 combining with 2 out of 20. Those are 400 possible gene pairs, with at worst case a stack of 220 bad gene pairs. 220 divided by 400 is 0.55. And at the worst case 0.55 times 10 is 5.5 which does not equal the six which you had said is necessary to have glasses.
