Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Go to an emergency service for sudden loss of vision, severe eye pain with headache or nausea, or an object that has pierced the eye.
Do not press the eye or try to remove an embedded object.
Rinse the eye continuously with plenty of clean, lukewarm water and arrange emergency help.
Remove contact lenses if they come out easily, but do not delay rinsing.
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Seek same-day medical care for:
Eye pain, strong light sensitivity, or a change in vision
A red, watery eye while wearing contact lenses
Marked redness, swelling, or difficulty opening the eye
A suspected scratch or something that remains stuck in the eye
Watering after an eye injury
3
Does any of this apply?
Book an appointment
Arrange a routine appointment with an optometrist, ophthalmologist, or primary care clinician if watering lasts, keeps returning, or interferes with daily activities.
You should also book an assessment if it mainly affects one eye, or if you have ongoing discharge, eyelid changes, or swelling near the inner corner of the eye.
The article also says
A chemical splash also needs immediate action.
Every sign above is quoted from the sofidex article on Watery eyes. If you are not sure, err upward — it is always reasonable to be checked.