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
A chemical splash is an emergency.
Rinse the eye immediately with plenty of clean water and seek emergency help.
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
Contact your eye clinic promptly if a contact lens becomes persistently painful, repeatedly falls out, or no longer gives its usual vision.
Remove the lens if it is causing pain, redness, or marked irritation.
Seek urgent same-day eye care for:
Sudden loss or major worsening of vision
A suddenly cloudy or white-looking cornea
New eye pain with watering or strong light sensitivity
Significant redness, discharge, or pain while using contact lenses
Eye injury or a chemical splash
Sudden vision loss should also be assessed urgently rather than waiting for a routine appointment.
3
Does any of this apply?
Book an appointment
Arrange a routine eye examination if your vision is becoming increasingly blurred or distorted, your prescription changes frequently, or one eye sees much less clearly than the other.
If you have diagnosed keratoconus, keep planned appointments even when your vision seems unchanged, because scans may detect progression before you notice it.
Every sign above is quoted from the sofidex article on Keratoconus. If you are not sure, err upward — it is always reasonable to be checked.