How long does it take for a cat's vision to come back after going blind from hypertension?

My senior cat with CRF (diagnosed more than a year and a half ago) is now also blind as a result of hypertension likely as a result of his CRF. He only has one eye, having literally lost the other to glaucoma five years ago. His blood pressure was 220 on April 23 and he's been taking 1.25 mgs (half a pill) of Amlodipine since then. We think we caught the blindness quickly since he only has one eye in the first place. His pressure in the "good" eye was normal so he does not have glaucoma. He won't get another BP reading until May 20. How long does it take for the vision to return, or at what point do you just resolve yourself with the fact that the vision will not return?