Is myopia genetic? Why have there been such huge increases in myopia in the last hundred years?
Nobody reputable claims that myopia (nearsightedness) is strictly (or even primarily) a genetic problem. While there are undeniably genetic correlations with nearsightedness, there is more and more evidence that the growing prevalence of myopia is related to the increase in education and literacy that has occurred all across the world over the last 100 years. This begs the question: to what degree is being forced to spend most of one's childhood in a classroom, learning to read and do math, maybe the cause of the increasing numbers of nearsighted people? -or at the very least a significant part of the cause.
One prominent theory is that sustained and repeated accommodation (muscular pressure inside the eye on the natural lens to see up close) in a growing child might be re-directing the normal amount of growth of the eyeball to an exaggerated degree. A bigger-than-normal eyeball is by far the most common correlation with myopia -the larger the eye, the higher the degree of myopia. A myopic eye has a close-up default focal point, making it less stressful on the eye (at the expense of distance vision). So in old age nearsightedness makes reading glasses less necessary! Think of all those monks in the scriptorium, copying the Bible one page at a time before reading glasses became common. This theory is certainly logical, but hard evidence for it is sketchy.
But how does one test this hypothesis? You cannot put reading glasses on just one eye of a growing child (and not the other) for both ethical and for practical reasons. One proposal is to atropinize the eyes of a child -to use a medical eye drop that paralyzes accommodation to see if there is less myopia later in life in such a group. Among the many problems with this is that atropine also causes a huge degree of dilation of the pupil as well. Anybody who has been dilated at the eye doctor's office and then tried to go out into sunshine knows what that is like.
I am confident that as science and technology advance, we will gain a deeper understanding of the actual causes of myopia. From that knowledge we will be someday be able to prevent myopia from developing. But this unfortunately is not "just around the corner."
Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic
