As blind as a bat.

This comparison describes someone as having very poor eyesight. It is an emphatic way to say that seeing clearly is difficult for them.

The expression is an exaggeration, not a precise account of what a person can see. It can convey frustration or amusement when someone fails to notice something.

Use it to emphasize difficulty seeing, especially when someone overlooks an object that others can readily spot. Because it compares a person to an animal, consider whether the tone suits the person being described.