Last I read, researchers had pretty convincingly isolated the primary cause as insufficient intense UV-bearing light (so, sunlight) exposure during a handful of

Last I read, researchers had pretty convincingly isolated the primary cause as insufficient intense UV-bearing light (so, sunlight) exposure during a handful of critical early childhood years, followed by genes as a distant second major risk-factor for near-sightedness. "Too much TV" or "too much reading" had been ruled out as meaningfully affecting anything, once isolated from the "too little bright light during certain ages" factor. The supposed mechanism is that intense light plays a role in getting the eye to stop developing and changing shape at the right time.