Carrots are of no use to your vision unless you are suffering a lack of vitamin A. If you are not, they will make NO difference. If you are suffering a lack of vit A there are lots of ways of sorting that out apart from carrots.
See wiki, as ever...
Lack of vitamin A can cause poor vision, including night vision, and these can be restored by adding vitamin A to the diet. An urban legend states that eating large quantities of carrots will allow one to see in the dark. This myth developed from stories about British gunners in World War II, who were able to shoot down German planes at night. The rumour arose during the Battle of Britain when the RAF circulated a story about their pilots' carrot consumption in an attempt to cover up the discovery and effective use of radar technologies in engaging enemy planes,