Some people may see flashes of light in front of one of their eyes like small sparkles. These tend to be in the extreme corners of your vision – they come and go and do not affect your vision. They don’t last for a defined length of time and may be more noticeable if you go from a light to a dark area. These are different to the zig-zag lines that often accompany a migraine attack. Migraine shimmers are a flickering of light, often on only one side of your vision, which then expands to the outside of your vision with a jagged pattern. This will often obscure part of your vision, either the left or right side. The shimmers usually disappear after 10-20 minutes and may be followed by a headache, although some people may get migraine shimmers without a headache afterwards.
Flashes occur when there is a pull on the retina. This might happen as the gel inside the eye becomes more liquid and collapses, which is more likely to happen as you get older. You may experience flashes occasionally, on and off over weeks or months. Flashes can also occur if you have a blow to the eye.
Floaters appear as black spots or something that resembles a hair or cobweb. These can be semi-transparent or dark and appear to float in front of your vision. If you have had these for a long time your eye and the brain learn to ignore them. Sometimes the number of floaters increases as you get older. Occasionally an increase in floaters can be a sign of problems inside the eye. Because they float in the jelly inside the eye, you will find that if you move your eye to try to look at a floater it will move away in the direction you move your eye. Floaters are sometimes only noticeable if you stare at a light-coloured surface or bright sky. Floaters can be a nuisance but most people learn to cope with them. Floaters are more common in people who are short-sighted however most of the time floaters are harmless and treatment is not required.
It is important to note that a sudden increase in floaters and/or flashes may be a sign of a more serious eye condition such as a retinal detachment. This is when the retina pulls away from the back of the eye and may also cause a blank spot or shadow in your vision. If you notice these you should seek immediate attention from an eye casualty department to check if there is any damage to your retina.