Prudie's advice is fine enough. But this is indeed tough. People are willing to accommodate many problems, but it's hard when they can't see the problem, and when they're not familiar with it. A "practical" solution may be to wear dark glasses... a "traditional" vision impairment may be easier to explain (dark glasses plus "I have difficulty distinguishing faces" could do the job).

I just think that having to explain your ailment to each and every person is a pain in the butt for LW.