Above) People unfamiliar with chihuahuas tend to assume they're all bug-eyed, as above. But a normal chihuahua does not have protuberant eyes. The bug-eye effect is one of many deformities that should disqualify a given dog from being bred, though it certainly can still be a wonderful pet. The condition of proptosis, or prolapsed eyeball. It leaves the eye vulnerable to scratches or more serious injury, thus to infection, blindness, and loss.
Below) Prolapsed eyeball effects in particular pugs, and ill-bred chihuahuas. The above photo is of Chico at age 13 after a visit to the vet with his eye hanging out. The eye was restored successfully, though it remained to be seen if Chico could see from it.