From blind spots in our retinas to an eye colour that didn't exist until recently, we count 

40 bizarre facts about our own eyeballs40 Human eyes blink an average of 17 times a minute. This equates to 14,280 times a day or 5.2 million times a year.

 39Blinking removes debris from the eye’s surface by spreading tears over it. The tears help moisten and lubricate the eyes. They also have anti-bacterial properties. 

38Eyes heal quickly. With proper care, corneal abrasions can repair within 48 hours. 

37Newborns don’t produce tears. While they do make crying sounds, their tears donut start flowing until they are 4–13 weeks old. 

36Approximately six in a thousand people are born with heterochromia irides. This is a condition where the person’s eye are two different colours.

 35A shark’s corneas are very similar to those of humans’. Because of this similarity, shark corneas have been used as replacements in human eye surgeries. 

34Schizophrenia can be diagnosed with 98.3% accuracy using a simple eye test that tracks eye movement abnormalities.

 33Dogs are the only species other than humans that seek visual cues from other individuals’eyes. Dogs only do this when interacting with humans. 

32‘Impossible’ or ‘forbidden’ colours are colours that are too complex for the human eye. Although it is impossible to perceive them under regular viewing conditions, they can be seen in special circumstances

 31The pupil of your eye expands as much as 45% when you look at someone you love. Similarly, a person's pupils may dilate when looking at someone they are sexually attracted to. 

30It's possible for your eyes to be sunburned. Prolonged sun exposure eventually leads to toa thickening of the eye tissue, which might require eye surgery. 

29Your retinas perceive the outside world as upside-down. The brain must then flip and make sense of the image.

 28Eye colour – or our perception of it – can change with lighting conditions. Neither blue nor green pigments are present in the human iris or ocular fluid. 

27Octopus eyes have no blind spot and evolved separately from vertebrate eyes. This is an example of convergent evolution.

 26Up until 10,000 years ago, brown was the only known human eye colour. This changed when a person living by the Black Sea developed a genetic mutation that made their eyes blue. 

25If one red eye appears in a flash photograph, there is a chance this person has a strand of treatable eye cancer called Leukocoria. For this test to work, both eyes must be looking directly at the camera.

 24Human retinas cannot detect the colour red. Our ‘red’ receptor only detects colours in the yellow-green spectrum; thus, our brains must combine multiple signals to perceived.

 23It’s possible for eyesight to improve with age. However, this can be a sign that something is wrong with a person’s overall health. 

22Your eye’s lens sits behind the iris and is roughly the size of an M& M candy. Developing a cataract in your eye is like developing a peanut in that M& M. 

21Our peripheral vision has a very low-resolution and is almost black-and-white. But we don notice this because our eyes move and fill in the details.

 20The visual centres in the brain are located at the lower back part of your head. This is why people with head injuries can sometimes experience temporary blindness.

 19Tetrachromacy is a rare genetic mutation occurring in 2% of women. It gives them an extra retinal cone, allowing them to see 100 million colours. 

18Staring directly into the sun will burn a spot in the retina, causing permanent blindness. This is called solar retinopathy. 

17Iris pigmentation develops over the first year of life. This means our eyes are darker now than they were when we were newborns. 16Our eyeballs grow just like the rest of our body. At birth, they are roughly 

16 centimetres wide; by puberty, they will have grown to a maximum width of 24 millimetres. 

15‘20/20 vision’ isn’t perfect vision. It simply means a person can see 20 feet in front of them with the same clarity as a normal-visioned person.

 14If you’re short-sighted, your eyeball is longer than normal. If you’re farsighted, it’s shorter than average. 

13The composition of tears differs depending on whether you’re crying, yawning or have an irritant in your eye. 

12In order for you to see, your brain must interpret the signals it receives from your eyes. Optical illusions occur when there are discrepancies between what your brain and eyes perceive. 

11Our eyes constantly make tiny involuntary jerking movements called ‘microsaccades’.These stop objects from fading from our vision. 

10Although the human eye is thought to be capable of detecting around 10 million unique colours, they only have the capacity to detect 30 shades of grey. 

9The refractive power of a human eye lens is approximately 18 dioptres, roughly one third of the eye’s total power. This makes an eye’s lens quicker than a camera’s. 

8Human eyes contain 107 million cells – all of which are light sensitive. Seven million cones help with the detection of colour and detail, while 100 million rods allow us to distinguish black and white. This means that less than a tenth of our visual receptors detect colour. 

7Human eyes have a small blind spot in the back of the retina where the optic nerve attaches. We don’t notice this hole in our vision because each eye works together to fill the other's blind spot. 

6The human eye can only make smooth (non-saccadic) motions if it’s tracking a moving object.A person cannot will their eye into making a smooth motion. 

5Pirates used eye patches to quickly adjust their eyes from above to below deck. They would have one eye trained for the bright light and the other for dim, below deck lighting. 

4All kittens are born with blue eyes, which – if they are going to do so – will change colour by around 8 weeks of age. 65–85% of all white cats born with blue eyes are deaf. 

3To detect nocturnal predators, many animal species will sleep with one eye open. One hemisphere of their brain is asleep while the other is awake. 

2Our two eyes give us depth perception. Comparing two images allows us to determine how far away an object is from us.

 1People generally read 25% slower from a computer screen compared to paper. Reports also suggest that late-night screen-reading may be damaging to our eyes.