"Michael S. Lorrey" wrote:
> I often wonder which came first: cathode ray tubes used for entertainment, or the
> trend of increasing numbers of short sighted, astygmatic, near blind people.... (me
> being one of those astygmatics...)
I had read a theory that eyesight is fine-tuned in mammals (including humans) via a feedback mechanism. As the child grows, the eyeball lengthens until it receives an inhibiting chemical(?) signal (sorry, it's been long enough that the details are as fuzzy now as my vision). The signal is generated by the cells stimulated by peripheral vision. The theory is that those cells do not receive enough light to release this signal (which is actually released gradually) until the eye is at the right length to focus sufficiently on the retina. There were some animal experiments that supported this theory.
Interestingly, the researchers were able to create near-sighted animals by giving them a "dull" field of vision, where everything was roughly the same brightness. Apparently the lack of contrast was sufficient to not convince the retina that focus had been achieved, and the signal was reduced/eliminated/delayed (not sure which). Speculation then is that the old wives' tale is true: spend your childhood with your nose in a book (low visual contrast, especially for peripheral vision where everything from the page looks gray), and you'll need glasses! Has anyone heard whether this theory has been validated or disproven?
If this theory holds, one would expect the current colorful TV and computer displays to be less damaging to eyesight than paper books.