I get this on day 3. It is as if you are only seeing half the picture .... like if your vision is made up of thousands of dots (sort of like a computer screen) then you are only seeing around 75% of the dots and the rest are blank). That is how I would explain it.
Bella Lucia had this same problem with her fast about 4 or 5 months ago. I call it the "sparkles" because even though you are looking at a solid object there is something kind of missing and it is also like a mild case of "seeing stars", but not exactly.
What you are talking about might be completely different to what I just described. It could be caused by lower blood pressure than usual or something quite harmless. I wouldn't worry about it.