Vet doesn't know why my cat is going back and forth between blind and seeing

My otherwise very healthy 21-yr-old neutered DSH Muzak has been literally alternating being blind and sighted for a week. I've watched his eyes go completely dilated for maybe five minutes and he begins to bump into things, and then back to normal for three minutes, etc. The vet says his eyes appear otherwise normal. His BP was around 165, she is putting him on alampidine. (She agreed he was blind when dilated.) She doesn't however have any idea why he should be going back and forth, she watched him do it. What could be going on? Thank you so much!

Hello!  Pacing back and forth can be a sign of distress and can also happen in neurological pathologies, which may fit with the impression of going temporarily blind / appearing confused (perhaps even the pre or post dromal phase of a fit)? It's okay that your vet doesn't know; there are infinite presentations in the world and there can be several explanations for most of them.  What is important, however, is whether they know how you can find out.  What did they propose as to the next stage?  There may be several ways forward depending on the exact presentation; perhaps bloods or a phone call to a specialist neurologist were possibilities?

Oh No!  I have incorrectly read your question.   Let me try again................. This is, indeed, a very strange case. Visual changes can happen at different levels.  First, at the level of the eye, for example cataracts etc.  I would expect most changes to be one-way, or at least healing to be slow eg with a corneal ulcer, but an increase intraoccular pressure that builds and  is then released again might account for a faster change, if the pressure was not reaching a certain peak that resulted in permanence. Another level at which blindness can happen is that of the brain.  This is more difficult to understand in a pet because they cannot explain what is going on and again, many brain changes tend to be one-way, or at least much slower to resolve than you seen to be describing. A third possibility may be that you are interpreting the behaviour incorrectly; that the eyes could be dilated for reasons of stress, for example.  However, it sounds as though your vet is reaching the same conclusion as you. So what would I do next? It depends on your vet, of course.  Personally, this is outside my area of expertise and I would try to get permission to refer the case to an expert in optics or neurology as described in my first answer. I would be very interested, if you were to do this, to know what was found.