I'm not so certain that the issue is the definition of the term normal, so much as it is the value (positive or negative) or association (healthy vs. unhealthy) the term implies in a medical or social context.
One of the most common reasons for blurry vision while wearing contacts is that your eyes are dry. Some people have a medical condition that causes dry eyes, called dry eye syndrome, but others' eyes are irritated by the contacts themselves.
If your eyes feel tired, sore or gritty or sandy, you may have 'dry eyes', or 'blepharitis' , or both. Dry eyes is a common problem as people get older, and in diabetes. The eyes may feel scratchy or gritty, as though there is something in them (foreign body sensation). They also be a little itchy, and they may be red.