Is it possible for a person to get a lazy eye after boxing for several years?

Yes: Boxing causes repeated trauma to the eye which usually withstands this due to a structure called the vitreous gel which holds things in place (mostly the retina). But sometimes this is not enough, the retina may detach, the vision drops and the eye drifts out of alignment - which is the term for a "lazy eye". If you must box, protect your eyes.