How much of nearsightedness is due to genetics?
It is certainly a fact that if both parents are myopic (nearsighted), the chances of their child growing up to be myopic is much higher than if only one, or neither, parent is myopic.
But this is not necessarily evidence of a genetic cause for myopia. Higher levels of education are also correlated with myopia, so it may be that the parents met in college or graduate school. Correlation is not the same as causation. Longer intervals of time spent outdoors and in natural sunlight in childhood is also inversely correlated with nearsightedness. So it is conjectured that a child, regardless of the parents needing or not needing glasses, may become myopic from spending a lot of time in childhood indoors reading or studying.
Nearsightedness is the growth of the diameter of the globe (the eyeball) to a degree in excess of normal and of the focusing system at the front of the eye. The factors causing this anatomic change are not at all well understood presently but cannot be attributed solely, or even predominantly to genetics.
Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic