I have only fasted for 3 or 4 days, but that sign of "poor vision" usually comes during the last day of the fasting. I had not paid much attention to it because of the many readings warning about it. As yourself, I only use reading eyeglasses, can not keep them on if I want to look at other things. I found out that is temporary, a day or two in my case. Later on, my eyes feel better than before attempting the fasting.