Flashing lights and floaters
The rear two thirds of the eyeball is filled with a jelly-like substance called vitreous humour. Any particles suspended in the vitreous may be seen as dark floaters. It is perfectly normal to have one or two floaters in each eye, especially as you get older. You will notice them more on a bright day, against a blue sky or a white wall. They will move around as you move your eyes from side to side
If you notice the sudden appearance of a large number of floaters you should see your optometrist as soon as possible. If that is not possible you should go to the eye department or the accident and emergency department of your nearest hospital
Flashing lights
If you experience flashing lights this maybe linked to a migraine attack, although is could be a more complicated problem, and you should seek professional advice urgently