Blue-eyed Tracy came out of the movie theater after a matinee. What kept Tracy from being blinded by too much sudden sunlight?

Flash blindness leads to reduction of size of the pupil.

Explanation:

when eyes of a person are exposed to a prolonged sunlight, the pupil in the eye gets smaller due to which everything looks black when come from severe sunlight to a normal room.

Also, vice versa is true if the eye of the person is exposed to too dark area, the size of the pupil gets increases from its normal size and when the person moves to the normal room, he becomes blind for some time.

Sam phenomenon happens in the given question.