Top 10 eyes facts

Blue-eyed people. The iris plays no role in the effect, but the blue-eyed people have relatively low melanin in the fundus as well. Therefore, they show a much stronger red-eye effect, as the light passing fundus is not absorbed by melanin. The role of melanin in red-eye effect is nicely demonstrated in case of heterochromia (one eye blue, one brown): typically, only the blue eye displays the effect.

Black. Owl's eye colour depends on the time of day in which they hunt. The ones that hunt during daylight have yellow eyes. The ones that hunt at night but also at the evenings and mornings have orange eyes. Black eyes are typical to owls that hunt only at night.

To better see in the dark. The sharpest image is produced by round pupils, and if cats weren’t nocturnal, they probably would have round pupils like us. But the vertical pupil, in combination with horizontal eyelids, gives the cat greater and more accurate control in different types of lighting. A cat may adjust the amount of light by moving eyelids only.

Sahara. The Richat Structure in Mauritania, also known as the Eye of the Sahara, was interpreted as an asteroid impact structure, but no evidence of shock metamorphism has been found. Today, scientists believe that it is a huge (40 km in diameter) and deeply eroded geologic dome.

Siberian Husky. Siberian Huskies are known for blue eyes. They commonly have one more unusual trait called heterochromia - a difference in iris coloration between the left and the right eye.

The giant squid. Giant squids have the largest eyes of any living creature except perhaps colossal squid – over 30 centimeters (1 ft) in diameter. Large eyes can better detect light (including bioluminescent light), which is scarce in deep water.

Goat. The horizontal pupils allow wide panoramic vision. Because goats' irises are usually pale, their pupils are much more noticeable than in animals such as cattle, deer, horses and sheep, whose similarly horizontal pupils blend into a dark iris.

Wearing sunglasses without UV filter causes the pupils to dilate and eyes to absorb more UV rays than they normally would without the sunglasses. Hence, it's much better not to wear sunglasses at all, than to wear ones without UV filter.

Tetrachromat. Man is usually sensitive to about 500,000 colors. Tetrachromacy is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cells in the eye. Organisms with tetrachromacy are called tetrachromats which can see up to 99 million shades.

Her mysterious smile. Mona Lisa is famous for an optical illusion aka 'the mysterious smile'. The illusion is caused due to peripheral vision as the focus of the viewer shifts from the eyes of the portrait to the lips of the portrait.