Direct quote from the CDC PDF on Hydroxychloroquine:

How long is it safe to use hydroxychloroquine?

CDC has no limits on the use of hydroxychloroquine for the prevention of malaria. When hydroxychloroquine is used at higher doses for many years, a rare eye condition called retinopathy has occurred. People who take hydroxychloroquine for more than five years should get regular eye exams.

FULL SEND