It is very common for people to notice dark or semi-transparent dots or squiggly lines in their vision from time to time. Some people describe them as “hairs, flies or cobwebs”, which they often try in vain to swat away. They appear to move across the vision, which has provided the basis for their technical name – ‘floaters’. Some individuals also experience ‘flashes’, which appear as small sparkles in their vision. Flashes and floaters are not usually something to be alarmed about but here we ‘shine some light’ on the topic so you know when to seek advice.

Who gets flashes and floaters?

Flashes and floaters occur more frequently in people who are short-sighted, or have had previous eye surgery, injury or trauma to the eye. Floaters gradually increase in number with age, and are a very common presentation in people aged over 50 years.

Why does it happen?

The space between the lens and the back layer (retina) of our eyes is filled by a jelly-like substance called the ‘vitreous’. Over time, this jelly naturally shrinks and separates, leaving small clumps of cells and particles floating in liquid (think of a shaken snow globe). They move across the vision with eye movements, casting a shadow on the light-sensitive cells at the back of the eye, which fire off signals that we perceive as floaters. While they are ever present, we tend to be more aware of them against bright, uniform light conditions such as a clear blue sky or a white wall in a well-lit room. As the jelly shrinks further and some parts start to come away from the back layer (retina). During this process, some people may notice an occasional flash or sparkle of light as they move their eyes – this is particularly apparent in dark room conditions. It occurs when there is a pull or tug on the light-sensitive cells of the retina in areas where the jelly is still attached. This is generally short-lived until the jelly naturally comes away completely from the back layer (retina).

Headaches and ‘visual aura’

Many people who get migraine headaches experience a visual display or ‘visual aura’ before, during or after the main event. This can range from seeing shimmering or zig-zag lines to parts of their vision blurring, dimming or even disappearing! Visual aura typically affects half of your field of vision and lasts between 10 and 20 minutes. It is caused by a temporary reduction in blood flow to the area in the brain that processes information received from our eyes (the visual cortex). They can be triggered by emotional factors (e.g. stress, shock, anxiety), physical causes (e.g. tiredness, poor posture, poor sleep) and dietary factors (e.g. chocolate, cheese, red wines, dehydration). It can be very frightening when this happens for the first time and especially if it occurs without a classic headache, so it is advisable to seek advice. In most cases, the visual aura is harmless and short-lived.

Should I get it checked?

Floaters are usually harmless and part of the natural ageing process of the eye. If you’ve had them for a long time, they’re not getting worse and your vision is not affected, then don’t worry. Your eye and brain get used to them so they become less noticeable over time. You can also lessen their effect on your vision by wearing dark glasses in brighter light conditions. However, you should seek further attention from an eye professional if you experience new floaters, or if you notice floaters with flashes, or a black shadow across your vision. These can be signs of something more serious.

Fun fact

The layer at the back of your eye (retina) sends signals to your brain in response to light. It also responds to physical pressure – you can test this by gently pressing on the side of your closed eye to stimulate the retinal cells. You should see a ring of light emerge on the opposite side!