Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Use emergency services for sudden loss of vision, severe or rapidly worsening eye pain, a bulging eye, an embedded object, uncontrolled bleeding, loss of consciousness, seizure, repeated vomiting, increasing confusion, new weakness, or difficulty waking.
Seek same-day medical advice for blurred or double vision, persistent eye pain, difficulty moving the eye, blood inside the eye, facial numbness, a deep eyelid cut, or significant swelling that prevents the eye from being assessed.
People taking prescribed blood thinners should have a lower threshold for contacting a clinician after a head or facial injury.
Routine home monitoring is reasonable when the injury was minor, vision is normal, the eye moves normally, pain is mild, and swelling is gradually improving.
The bruise should change color and fade rather than become increasingly painful or swollen.
Arrange a routine medical review if the bruise is not improving, remains unexplained, or happens repeatedly.
A clinician should also review easy bruising elsewhere, frequent nosebleeds, or other unusual bleeding.
These symptoms may need an assessment of medicines or blood clotting.
After a diagnosed concussion, eye injury, or facial fracture, attend the recommended follow-up even if the bruise looks better.
Vision testing or specialist review may detect problems that cannot be judged from appearance alone.
Every sign above is quoted from the sofidex article on Black eye. If you are not sure, err upward — it is always reasonable to be checked.