Up until 2002 (then age 23) I had 20/20 vision.  Over the course of a
few months I started having problems focusing on things - especially
text on computer screens and small print in books and magazines.  I
went to an eye doctor.  She diagnosed me with astigmatism and gave me
some glasses.  That helped immensely and I took to wearing the glasses
all of the time.  However, about 4 or 5 months ago, I've noticed that
my vision seemed to be getting worse again suddenly.  The glasses
didn't help so much anymore and sometimes seemed to make my vision and
eye fatigue worse.

I have since heard that astigmatism generally gets worse over time with
the use of corrective lenses.  (Is this true?)  About 2 weeks ago I
decided to stop using my glasses and for about a week it seemed to
actually help my vision about 50% of the time and my eyes were less
tired at the end of the day.  So I kept them off.  This week, though,
it seems to be getting worse again and I'm finding myself considering
going back to the eye doctor and getting a new prescription since my
eyes have clearly diminished in quality over the past few years.

I guess my question here, though, is what causes astigmatism to begin
with and are there any ways to correct it or at least attempt to
reduce/eliminate the degradation?  Is it true that astigmatism gets
worse the longer it is corrected?  If so, why?

And perhaps most importantly:  What would cause the sudden onset of
astigmatism to begin with - especially with no prior vision problems on
my part.  Back in 2002 I was concerned about how quickly it seemed to
appear and my doctor had nothing to say about it when I expressed that
concern.  The only people I've known who went from no glasses to
wearing glasses later in life have been in the 40-50 age range and the
excuse given is always that it's just part of getting old.  The fact
that this hit me at age 23ish has me slightly concerned that by the
time I'm 50 I'll be blind or something!

Thanks,
Sean