Myopia, or nearsightedness, is extraordinarily common -- affecting as much as 50% of the population of the
United States. Given the large number of people who need
glasses or
contact lenses to correct this
refractive error, one might wonder how
nearsighted people managed in the hundreds of thousands of years before
spectacles were
invented. From what is now known about myopia, most people's vision may have been considerably better in
ancient times. The basis for this assertion is the surprising finding that the growth of the
eyeball is strongly influenced by focused light falling on the
retina. This
phenomenon was first described in 1977 by
Torsten Wiesel and
Elio Raviola, who studied
monkeys
reared with their
eyelids
sutured closed. This procedure, obviously enough, deprives the eye of focused retinal images. Animals growing to
maturity under these conditions show a remarkable elongation of the eyeball. The effect of this deprivation is a local one, since the
abnormal growth of the
eye occurs in
experimental animals
even if the optic nerve is cut. In fact, if only a portion of the retinal surface is deprived of focused light, then only that region of the eyeball grows abnormally.
Although the mechanism of light-mediated control of eye growth is not fully understood, many believe that some aspect of modern civilization -- perhaps reading and writing -- interferes with the normal feedback control of vision on eye development, leading to abnormal elongation of the eyeball. A corollary of this hypothesis is that if children wanted to improve their vision, they might be able to do so by practicing far vision to counterbalance the near work "overload". Practically, though, most people would probably choose wearing glasses or contacts rather than the onerous daily practice that would be required. Not everyone agrees that such a remedy would be effective, however, and some investigators and drug companies are exploring the possibility of pharmacological intervention during the period of childhood when abnormal eye growth is presumed to occur.
Neuroscience, Sinaur Associates (QP355.2.N487 1997)