how do you tell if a cat is hurt or needs too go to the vet?

If your cat’s behavior or condition suddenly changes - eating patterns, sleeping patterns, sudden aggressiveness/personality change, going outside the litterbox when they didn’t before, constant appearance of the third eyelid, noticeable fever, vomiting more than once, diarrhea, etc - then he may be sick.

If your cat’s third eyelid is visible in just one eye but not the other or he’s keeping it closed, it’s possible he’s scratched his eye on something or has conjunctivitis (”pink eye”). I would definitely take him to the vet to have it looked at your cat could lose that eye if there is an infection.

There are some descriptions of a variety of different eye problems that cats can develop in this thread: http://www.cats.com/question/cathealth/eyeear/can-cats-get-human-eye-problems/?search=human%20eye%20problems

I agree with telegramsam - become familiar with your cat’s normal behavior patterns because sudden changes can indicate a problem that should be evaluated by your vet.

HI
take you cat to the vet,He/she can have an intection in the eye.

thanks for all the great answers