We've have a few threads before here at ETS about spare glasses. But I just ran across an interesting emergency eyeglasses product that I may have to try. It's adjustable for prescriptions within a 12 cylinder range! Obviously the best option is to have your own prescription but if it works as claimed it would be a great addition to group preps.
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“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman