Given that this is a unilateral finding (only on one optic nerve), this sounds like it is likely an ischemic optic neuropathy. In your age group with a history of disease that effects blood vessels (hypertension and diabetes, even if they are well controlled), this is the most likely entity.
For the most part, the vision that you have right after the event can tell you something about your visual prognosis. If your vision is quite bad (cannot even see the big "E" on the chart), then it's likely your vision is not going to improve significantly and therefore you would end up with a permanent disability. If your vision is still respectable (you can still make it out to 20/60, 20/70 on the eye chart, then your chances of retaining useful vision are relatively good; these are the people who tend to do the best. Even still, if this is an ischemic optic neuropathy, you will likely be left with some permanent deficit, even if it is only a small area where you don't see. The majority of patients with this do not return absolutely to how they were beforehand.
It sounds as though you are doing what is right in controlling your high blood pressure and diabetes. One of the most important things to consider is to try not to have this kind of an event in the other eye. Do you take aspirin? If not, you should consider talking to your primary care doctor and seeing if that's something that you can do. In addition, I would recommend that you speak to your primary care doctor about taking your high blood pressure medications as far away from when you go to sleep as feasible. The reason being is your high blood pressure medications tend to bring your blood pressure, which goes lower when you sleep, even lower still and at some point there can be a lack of pressure in the pump, so to speak, bringing blood to the optic nerve. This can lead to an ischemic optic neuropathy. So if you're taking blood pressure medicines all at night, ask your primary care doctor if you can change some of them to the morning. If there are some you are taking two or three times per day, see if he/she will allow you to take the later doses in early evening.
Again, I cannot know for sure that this is what's happening because I haven't examined you, but this sounds like the most likely problem you have been plagued with.
Does this make sense the way I've explained it?
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Disclaimer: My opinion is solely informative and does not constitute an informed medical opinion or recommendation. For an informed medical opinion and/or recommendation you must see an eye doctor.