A Twitter post illustrating how people with astigmatism see light has gone viral and caused thousands of social media users to realise they themselves suffer from the common eye condition.
The tweet by Unusual Facts on 25 March depicted two shots of cars caught in traffic on a motorway at night, their red rear lights flaring in one but not the other.
It has been retweeted 23,000 times and liked almost 55,000 times at the time of writing, as people attempt to decide which of the two best represented their own experience of vision.
The image on the left captures what would be seen by those with astigmatism, which, as Unusual Facts suggests, relates to having a slightly curved cornea.
For those unfamiliar with the condition, the NHS defines it accordingly:
Astigmatism means your eye is shaped more like a rugby ball than a football, so light is focused at more than one place in the eye.
This can cause: blurred vision, headaches and eye strain.
Essentially, the curves of the cornea on the front surface of the eye and the lens inside it are mismatched, meaning incoming light rays do not refract as they would in the case of a perfect eye. Instead, light strikes the retina at multiple points, creating a blurring effect.
The condition is most commonly present combined with another refractive error like short-sightedness or long-sightedness.
The reaction to the lens flare tweet was largely one of surprise:
Others were sceptical:
It's all true of course and no cause for concern, although you should obviously visit an optician if you experience any discomfort at all relating to your vision.