The largest "eyes"
The Helix Nebula, also known as The Helix, was discovered by Karl Ludwig Harding at 1824. Because of the characteristic form Internet users and journalists called it as the “Eye of God”.
The Nebula is located in the constellation Aquarius about 650 light-years away from the Sun, and spans area of space about 2.5 light-years. It is probably the biggest “Eye” in the Space.
The Richat Structure, also called Guelb er Richât, is geological formation located in the western part of the Sahara Desert in the territory of Mauritania. Its diameter is about 40 km, therefore it is possible to be seen entirely from Space only.
Due to the appearance it is called “Eye of the Sahara” or “Eye of Africa”. The structure is ideally round. It formed about 600 million years ago apparently as a result of tectonic shifts of the Earth's crust.
Unusual eyes of animals
It is believed that in animals both eyes must be the same and see the same, but investigations of starlings eyes (Sturnus vulgaris), performed by prof. N. Hart of the University of Queensland (Australia) in 2000 showed that in the right eye of the birds there are more cones responsible for the recognition of movement, and in the left for color perception. Scientists assume that the starlings eyes have different functions, so the birds alternately examine objects with one and then with the other eye.
The six-eyed spookfish (Bathylychnops exilis) living in ocean near the Azores at depths of around 500-1000 meters has unique optical system: its eyes are divided horizontally into two unequal parts. The main, large, eyeballs look up. The other pair is downward-pointing spherical organs housed within the lower half of its large eyes. They were once believed to be light-producing organs – bioluminescence is a common phenomenon among deep-sea fishes. Closer examination, however, revealed their true identity. In reality, these organs, now referred to as secondary globes, are accessory eyes. Each of these globes possesses its own lens and retina and probably serves to increase the spookfish’s sensitivity to light (photosensitivity) within its dimly lit undersea realm. But this is not the only anomaly of its optical system. Scientists discovered one more surprise: behind the acsessory eyes is a third set of ‘eyes,’ even tinier than the secondary globes, but less sophisticated. These ‘eyes’ lack retinae. Instead, they serve merely to direct incoming light into the spookfish’s principal pair of eyes, thereby enhancing these latter organs’ powers of vision.
A chameleon, when hunting, to not betray its presence, does not move its head, but only rotates eyes. Chameleon eyes can rotate and focus independently of each other and see different objects at the same time. This gives them a 360 degree view around their body, and while one eye is watching the prey, the other looks around for danger. Also, chameleons have very good eyesight as for reptiles, that allows them to see small insects from a long distance (5-10 m).
The four-eyed fish Anableps anableps living in the Caribbean Sea has eyes located on the top of its head and divided horizontally into two halves, each of that has its own iris and retina. This allows the fish swimming at the surface of the water to look out for insects using the upper halves of eyes, and to monitor situation under the water using the lower ones. The lower part of the lens in the fish is thicker than the upper one that provides good vision in the water.
Optical illusion is a mistake of visual perception caused by the inadequacy of the visual image correction with by our brain. Optical illusion occurs when the observer consciously or unconsciously explanes the observed picture in wrong way. It may also be due to physical reasons (“broken spoon” in a glass of water).
Below you can see examples of optical illusions.
Fig. 1, 2 - the illusion of movement
Fig. 3, 4 - illusion of color perception: on the dark background the same color seems different from the color on the light
Fig. 5 - when fixing the gaze at the crossing of rhombs, the black dot “wanders” - changes its position.