It is highly likely that you have a
Vitamin D deficiency. Check with a doctor. It is unlikely that your poor
vision is associated with the hair loss.
Now, if you are having REALLY BAD headaches, or SUDDEN headaches (not just scalp pain) that coincide with fuzzy vision, then you really need to look into the possibility of high blood pressure, possible strokes or aneurysms, or a tumor. If you just have bad vision requiring glasses, then you are probably fine.