Hello, Welcome to healthcare magic. I have read your question and understand your concerns. I do understand that you are worried about your symptoms. it is good that your MRI, CT scan and blood counts are normal. This rules out a space occupying lesion in your brain which is what majority of patients are worried about when they have a headache along with visual disturbances. Prediabetes is unlikely to cause blurred vision in you. Very high blood glucose can cause blurred vision but in prediabetes, the blood glucose is not that high. Further, by starting metformin your 2 hour postprandial glucose is in normal range. Blurred vision by itself can cause a tension type headache due to straining of nerves. I would advise you to see a ophthalmologist so that you could have a full eye check. I hope this answer has helped you. Thank you Regards Dr Sunita Sayammagaru