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
Get urgent or emergency eye care for:
Sudden loss or major reduction of vision
A dark curtain or shadow moving across your sight
New flashes of light with many new floaters
Severe eye pain, redness, nausea, or headache
Vision changes after an eye injury
These symptoms can have causes other than night blindness, including retinal detachment or a sudden pressure problem inside the eye.
Rapid assessment can be important.
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 prompt medical advice if poor night vision develops after weight-loss surgery, with severe dietary restriction, or alongside a condition that affects nutrient absorption.
Vitamin A deficiency should be tested and treated rather than managed with supplements alone.
3
Does any of this apply?
Book an appointment
Arrange a routine eye examination if you have persistent difficulty seeing at night, need much more light than before, or notice that dark adaptation is worsening.
Make an earlier appointment if the change is new, affects driving, or comes with narrowing side vision.
Every sign above is quoted from the sofidex article on Night blindness. If you are not sure, err upward — it is always reasonable to be checked.