If you can get a Xerox copy, use yellow high-lighter on the problem letters/words and then use a black light; highlighting the word helps the black light to work even better. Do not do highlight an original, just use the black light on it.
This works on over 90% of all copies, I can't say the percentage of documents. I haven't had the luxury of handling originals, beyond newer vital records. With the use of a black light ($10.00 from a company who sells through Amazon), my eyestrain is over.
Source: Just tried this and it worked so well I had to let others know
By Neko from OR