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
Several different eye conditions can cause this, and some need immediate treatment.
Call emergency services if a vision change occurs with facial drooping, arm or leg weakness, difficulty speaking, loss of balance, or a sudden severe headache.
These can be signs of a stroke or another neurological emergency.
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 a same-day eye assessment for a new, sudden loss or blurring of vision, even if it is painless.
Get urgent help if you develop:
A painful red eye, headache, or nausea with reduced vision
A sudden shower of floaters, flashes, or a curtain-like shadow
A major new dark or missing area in your sight
Rapid worsening between scheduled eye appointments
Do not wait for a routine appointment if a sudden new symptom develops.
3
Does any of this apply?
Book an appointment
Routine follow-up is for monitoring stable vision, retinal swelling, eye pressure, and treatment response.
Every sign above is quoted from the sofidex article on Retinal vein occlusion. If you are not sure, err upward — it is always reasonable to be checked.