Sometimes you may see an unexpected flashing light in one or both eyes, without an accompanying external source such as a bright light. If you do experience this, you should know that flashes (as well as floaters, another common symptom) are actually fairly common and may not require any urgent medical treatment.

Flashes can occur on their own or with floaters. They look like lights or lightning streaks and are usually more noticeable at night or in dark environments. They are usually caused by a 'pulling' of the vitreous gel at the back of the eye. This can be a harmless occurrence, but you should see your optometrist for a check-up to rule out anything more serious.

If you see flashes suddenly and in a greater amount than usual, you should definitely see your optometrist or doctor immediately. A sudden and unexplainable surge of these types of flashes can indicate the vitreous fluid inside your eye is pulling away from the retina, the light-sensitive layer at the back of the eye.

This increases the risk of the retina itself becoming detached or torn away from the inner section of the eye, which means your vision will be affected. In this case it is crucial to seek help right away, as the earlier a retinal tear is detected, the better the chance of it being reattached successfully.

At other times, seeing a flash of light can also be a common occurrence after receiving a significant injury to the head area - also known as 'seeing stars'. On the other hand, if your flashes appear more like jagged lines or heat waves and last for between 10 and 20 minutes, the cause is usually attributed to migraines. If you are worried about seeing flashes in one eye, it's best to consult your optometrist for more information.