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What exactly occurs in the eyes to make some people short-sighted and others long-sighted? (continued)

Tony Harding, Sarsfield, Victoria, Australia

Time spent outdoors may make it less likely that people become short-sighted because of exposure to different wavelengths of light, as a previous answer suggested, but I suspect the explanation is simpler than that.

I suggest that changes in eyeball shape that give rise to long or short-sightedness are a consequence of the growth spurt at puberty when the eye must enlarge but retain clear vision. If you are a reader, the eye adapts to provide clear vision at the normal distance between book and reader while if you spend most of your time outdoors it will adapt to accommodate more distant views.

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