Interesting facts about vision

Swedish biologists Dan-Erik Nilsson and Suzanne Pelger of Lund University simulated the history of the evolution of the eye on a computer. In this model, it all started with the appearance of a thin layer of cells that are sensitive to light. Above him lay a transparent cloth through which light penetrated; underneath is an opaque layer of fabric.

Individual, minor mutations could change, for example, the thickness of the transparent layer or the curvature of the photosensitive layer. They happened by chance. Scientists only introduced a rule into their mathematical model: if a mutation improved the image quality by at least one percent, then it was fixed in subsequent generations.

In the end, the "visual film" turned into a "bubble" filled with transparent jelly, and then into a "fish eye" equipped with a real lens.

Cats, like any nocturnal predators, see well at night. In the dark, their pupils dilate markedly, reaching a diameter of 14 millimeters. In humans, the diameter of the pupil does not exceed eight millimeters. This means that a cat needs much less light than a person to distinguish between objects and other animals.

In addition, a cat's eye is designed differently. In its depth, behind the retina, there is a special reflective layer - Tapetum lucidum. It casts light into the cat's eyes. This is why a cat's eyes glow yellow or green in the dark. Thanks to this feature, the visual cells located on the retina of her eyes receive twice as much light.

There are two types of light-sensitive cells in the human eye: rods and cones. The sticks distinguish between dark and light. Thanks to them, we see at least something at night. The cones perceive color. A cat has the same two types of cells. But if a person has four sticks for one cone, then a purr has twenty-five! This is why cats can see colors much worse than us. So, red is completely inaccessible to them. The cat's world looks faded and pale. Scientific wisdom says: "During the day everything around the cat is gray." Only certain colors - for example, blue - brighten her horizons.

The birds' eyesight is phenomenal. So, a kite from a height of 2000 meters will notice carrion lying on the ground. The eyes of a bird of prey can rightfully be called a unique pair of binoculars.

The bird's eyes are arranged differently than ours. A person has a “yellow spot” in the middle of the fundus. There are the most light-sensitive cells here. This is the area of ​​the most acute vision. There is only one “yellow spot” in our eye, but birds have two. They can equally well see two objects at once, located to the side from each other. So, a thrush at the same moment can gaze intently at the worm, which he intended to seize, and at the cat, which is sneaking towards him.

The second "yellow spot" lies a little deeper than the first. It enlarges the object the bird is looking at. That is why the bird has binoculars eyes.

If we take the eagle's visual acuity to be 100 percent, then the human vision is only 52 percent of the eagle's vision. But what are the abilities of some other animal species:

octopus - 32 percent of the eagle's vision;

jumping spider - 9 percent;

cat - 7 percent;

goldfish - 5 percent;

rat - 0.7 percent;

fruit fly - 0.07 percent;

planaria (ciliary worm) - 0, 009 percent.

Visual acuity is also related to how well the eye can see objects located at different distances. To do this, he "adapts" to them. This property is called accommodation. In humans, like in other mammals, the curvature of the lens changes. When we consider an object lying close, the lens bends more strongly, and this changes its refractive power, or optical power. This ability is measured in diopters.

The young man easily shifts his gaze from the near background to the background. The lens of his eye is very elastic and changes its refractive power by 14 diopters. But his beloved dog is deprived of this talent. In her, the optical power of the lens can increase by only one diopter. With such natural inclinations, you can see well either at a distance from yourself, or directly in front of you. So, farsighted hounds.

Cats are also best able to make out objects that are to the side of them. They see especially well at a distance of two to six meters. It is very convenient for hunting birds or mice

The lens of the eye of the cormorant is especially surprising. Its optical power changes by 50 diopters. Therefore, the cormorant can see equally well in the air and under water.

And a few more facts:

Take a close look at the Big Dipper. If near the middle star, in the handle of the bucket, you can clearly see a small star, then your eye has normal sharpness. This method of checking eyesight was adopted by the ancient Arabs.

It is impossible to sneeze with your eyes open.

After a minute of being in the dark, the sensitivity of the eyes to light increases 10 times, after 20 minutes. - 6 thousand times.

The eye of large whales weighs about 1 kg. Vision in cetaceans is monocular. Many whales cannot see objects in front of their snouts.

Cockroaches also have infrared vision. A cockroach's mustache not only touches, but also sniffs.

Illumination of the eyes with red light for 2-3 minutes increases night vision sensitivity for half an hour. This method was used by army intelligence officers, back in the First World War.