What kind of prescription?

Question

number have to be reached so that he or she wouldnt find their way back home without glasses or contacts

Answer 1

it would depend on the familiarity of an area or region.  The person could have a moderate prescription and not be in a familiar area and not get to where they wanted to, someone that is blind or nearly blind can get around in a familiar environment.  SO not really understanding much else, i can not answeryou any clearer.

Answer 2

I would imagine most anyone regardless of their eyeglass prescription right up to -10.00 could "find their way home".