I’ve never gotten into a mess resulting in a black eye, even if I am a little clumsy, but I’ve seen a couple—never any serious though.
For the most part, a black eye is just a bruise around the eye and can be treated as any other bruise. However, because of the location and depending on how you got the black eye, you may want to have it looked at by a professional. Because it is around the eye, there’s always the chance that a more serious injury has a occurred without detection or that complications could arise. I say all this, but at the same time, a black eye can look worse than it is because the tissue around the eye is fairly loose and can swell easily.
So, other than the obvious bruise, a black eye can also come with blurry vision and pain and still be pretty normal. The eye may even swell shut but this is still normal for a minor injury. There should be more concern if the afflicted person has any of the following symptoms:
Cannot move their eye
Loss of consciousness
Blood/fluid coming from the ears or nose
Blood visibly in the eyeball
A severe or ongoing headache
A doctor can usually tell based on a physical exam how serious a black eye may be but there is always the chance that there are fractured bones or something may have gotten into the eye.
A normal black eye (that doesn’t have fractures or other complications) can be treated at home. An ice pack or ice compress can be used for the first day or two to reduce the swelling; just apply once every hour for 15-20 minutes. A bag of frozen vegetables can also be used, but do not use a piece of raw meat—the cartoons are wrong and this is dangerous. A heat compress can be used after the swelling has gone down to help fade the bruising, but otherwise, this will go away on its own with time.
Info: American Academy of Ophthalmology: https://www.aao.org/eye-health/diseases/black-eye