> The dominant hypothesis now is that exposure to daylight is the main variable. Which is obviously wrong. The main variable is the time the eye spends at a sh

> The dominant hypothesis now is that exposure to daylight is the main variable. Which is obviously wrong. The main variable is the time the eye spends at a short focal length. Like every other part of the body, the eye adapts to the stresses it experiences. Focusing on nearby objects for extended periods is stressful for a normal eye and as is the case for so many stressors, the body adapts[1]. This is easily seen in that ceteris paribus a person with myopia can comfortably focus on much closer objects than someone with normal vision. Incidentally this means that corrective lenses can actually cause myopia to progress. Contrariwise a prescription can be written such that there is an effective training stimulus to reverse myopia[2]. However, that won’t fix the decreased focal range due to age related hardening of the lens of the eye. [1] See Selye for details. [2] Inexplicably, most optometrists refuse to do so.