Hi, I'm getting ready to buy a backup pair of glasses, and they'll be
the first pair of glasses I'll have been able to really research, since
I've finally learned my lesson (+my prescription is settling down...
only changing by a decrease of -0.25 spherical power diopter every 2
years, and an increase of -0.25 cylinder power in one eye (OD) over the
last 4 years.

Anyways, I'm curious both about lens thickness and optics. I know that
the frame matters a lot to thickness - and my current frames are the
tiniest ones I've had yet (I'm 21, on my 6th pair of glasses, and I've
noticed every pair I get gets smaller). I also got my first contact
lenses this time! But I don't really like wearing them (Ciba
O2Optix)... My eyes get tired more easily, I get more headaches (partly
since unlike glasses I can't just take them off to read and use the
computer), etc... Anyways, my current frames are these:
http://framesdirect.com/framesfp/Candies-tapfm/r.html  (size
46-18-130). They were bought at Pearle Vision and I have Seiko 1.60
index aspheric lenses that were stock and stock AR coated. I'm very
satisfied with the thickness and optics - though I don't care for the
greenish AR (before I had Zeiss Gold ET on a non-aspheric, unnamed,
1.60 index). Pearle Vision did have to redo them *three* times until I
got a pair of lenses that didn't have tiny scratches in the coating!!!

I LOVED the Zeiss Gold ET but needed glasses-in-an-hour (and that meant
stock lenses) this time (my old ones literally fell apart when cleaning
them one day - they were a cheap plastic frame with tons of tiny cracks
in it)

Historically, before my last pair I had always had what my parents
bought for me - uncoated polycarbonate. The stuff gave me terrible
headaches from glare and the chromatic aberration really bothered me.
But I was a kid and teenager - I didn't know there WERE any other type
of glasses, and the possibility of different lens materials being
optically better (I was TOLD as a kid by opticians that polycarbonate
was "far better than plastic") and coatings was never presented to me.
I was told by a good friend of mine when complaining about how I hated
glasses that I needed AR coating and better lenses - both he and his
(then ten, now twelve year old) daughter had high-index AR coated
lenses for the same problems I had and both said they made all the
difference in the world - and they do!

Anyways, sorry for all that but hopefully it helps you provide me
recommendations for the best cost for money for me in a backup pair of
glasses. Are Costco's glasses decent? Anywhere else cheap? In a frame
the size of the one I'm wearing now - what will the edge thickness of
the different materials on the market? How would CR-39 look in my
prescription with my frame size - these 1.60's are SO thin in this
frame, I'm thinking CR-39 might not be TOO bad for backup glasses. How
would they compare optically? What are the best (non-glass) optics I
can get? What is cheap and still great for backup glasses (which I'll
probably be wearing quite often - they won't be sit-in-a-drawer backup,
they'll probably be a slightly different style and color so I can match
outfits better than being stuck with one pair)

Thanks for any recommendations you can make - I've learned my lesson
that lens and coating choices can change how I see my world -
literally. Headaches as a kid are gone. Hate for wearing my glasses -
70% gone. (Of course, part of that is finally getting some nice tiny
frames vs. the huge things I used to wear (at the encouragement of the
optician!) But the AR, in addition to getting rid of glare also makes
me feel better about wearing them). That's why I want to get some
professional (and experienced amateur :) :) :) ) opinions before I go
shopping for this pair!

Thanks so much in advance,

Mark