So I looked it up and according to the first source I found and at the top of the page of the article

A deer’s eyes consist of more rods than cones, which is why it is able to see very clearly, even at night. However, when a car’s headlight beam falls into their eyes, the deer becomes blinded by the bright light. Until its eyes adjust to that heightened level of brightness, a deer will keep standing there, which makes it look like the deer is rooted to the spot