I have a 3-4 day black eye. i was doing cold and hot application on the eye so it can heal faster. saw a er doc on my 4th day and she said no point. ?

Use logic: I am going to assume that the eye underneath is untouched and sees well - so the only problem is the skin around the eye. The usual rule for a contusion like this is to apply cold for 2-3 days which staunches bleeding and minimizes swelling. After that heat will accelerate the healing and absorption of what blood has leaked into the tissues. Hot and then cold repeatedly is not logical.