The bottom line here is one word: presbyopia.
As a person ages, they gradually lose the ability to "accommodate"
where the focus of the lens of the eye shifts from distance to
near. It is our current understanding that this is caused by a
decrease in the lens elasticity. Normally the ciliary muscle in
the eye contracts, the 'zonules' which hold the lens in place
relax, and the lens 'bulges' somewhat, increasing the power of its
focus. This shifts the focal point from far to near. As one ages,
the loss of lens elasticity results in less and less change in the
power of the lens when the ciliary muscle contracts. There are
some current challenges to this as the physiologic explanation, but
this is the currently accepted one.
A child can accommodate extremely well, and the 'near point' (the
closest point which can be focused) is quite near to the eye. As
you age, this near point gradually gets further and further out, as
accommodative ability is lost. It reaches a 'critical' point
generally in the 40's, as the near point pushes reading material
further and further out. The solution is reading glasses, which is
basically just a plus lens (typically starting about +1.25
diopters).
I am not aware of any studies that suggest computer use, or
prolonged reading or close work, have any effect on the rate of
loss of accommodation. In fact, it could be argued (or rather
hoped!) that prolonged use of the accommodative process might keep
it stronger for longer than it would otherwise, but this is just a
theoretical argument.
So to the best of my knowledge, there's no reason to blame your
computer (LCD, CRT or otherwise), or any other activity on your
part, for your need for reading glasses. It's just the passage of
time. I was determined that I would be the "exception that proved
the rule" and postponed getting reading glasses, hoping I would
never need them. I sit here with a pair of +1.25 reading glasses
perched on my nose as I type this. Sigh....
Hope this helps! As they say, getting older is bad news, but it's
better than the alternative.
--
Don
http://www.dlcphotography.net
