Hi there,
High BG levels change the osmotic pressure and balance within the eye which can alter the ability to properly focus and cause blurring. If you have extended periods of hyperglycemia (high blood sugars) then this can be a side-effect - if good control of sugars is regained this can and should subside. It is unlikely that you would have retinopathy at this stage however this is something you should be regularly (once per year) screened for.
J