To the Editor.
—I wish to take issue with the conclusions of Dr Zadnick and colleagues1 that the slightly greater incidence of myopia and long eyes among the school-age children of myopes is evidence for a strong genetic determination of myopia. I would like to suggest how environmental influences might produce such results, to correct a technical error, and to point out a misleading interpretation.Consider that there are two mechanisms for clearing blurred images: accommodation, which rapidly adjusts the optical power of the lens, and emmetropization, which slowly adjusts the length of the eye during growth (shown clearly by animals compensating for myopia or hyperopia imposed by spectacle lenses2). Because the two mechanisms act in parallel, the better accommodation is, the more in focus images would be, and the less the eye would need to elongate and become myopic to clear the images. Conversely, poor accommodation might