@ehdog

If the spot is always physically present but you only notice it sometimes, such as on plain white surfaces, it is likely related to a migraine aura, visual processing quirk, or eye strain. The important points that show it is not caused by hypertension are:
Hypertensive vision problems do not appear only on certain backgrounds, they are persistent and clearly noticeable across all visual situations. They do not come and go in awareness, the loss is there every time you look, even if your brain partially filters it out. They occur in the context of long term, poorly controlled high blood pressure, which you do not have.
Because your blood pressure is well controlled and your readings are consistently normal, this spot is not caused by hypertension.