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How our eyes make sense of light

How our eyes make sense of light

Eye: The sight organ. There are a variety of components to the eye. Such elements include the cornea, iris, eye, lens, retina, macula, optic nerve, choroid, and vitreous, but are not limited to. The cornea is the transparent front window of the eye, transmitting light into the eye and concentrating it.

Although baby’s eyes grow at birth, it takes up to 2 years to completely grow eyesight. After birth and again during puberty, the eyes develop steadily until age 20 or 21 when they stop increasing in size. Eyes keep on rising in weight and experiencing age-related changes.

Eyes importance

Our connection to the world is the human senses. Our eyes are by far the most important organs of thought. By our sight, we experience up to 80 per cent of all experiences. And when other senses like taste or smell stop functioning, it’s the eyes that best protect us against danger.

Regardless of their distinct forms, certain nerve cells are called rods and cones. Rods also allow the eyes to detect movement and help us see in dim light and in the evening. In the eye, these cells transform the light into electric impulses. Those impulses are sent to the brain by the optic nerve, which creates an image.

What areas of the body are these?

The front part (what you see in the mirror) is;

  • Iris The element of color.
  • Cornea a distinct cloud above the iris.
  • Pupil The circular black opening in the iris that lets light in.
  • Sclera The eye dark.
  • Conjunctiva a thin film of tissue that covers the entire eye front except the cornea.

How do our eyes see?

  • The structure of the human eye is so complex that it is hard to believe it is not the result of intelligent design, but by looking at the eyes of other species, scientists have shown that it has developed very gradually over the course of around 100 million years from a simple light-dark sensor. It functions very close to a mirror, with an aperture through which the light enters a focusing lens, and a light-sensitive membrane at the rear.
  • The amount of light that enters the eye is regulated by the circular and radial muscles in the iris, which contract and relaxes to alter the size of the pupil. The light first passes through a tough protective sheet called the cornea, and then travels into the lens. This flexible structure bends the light, focusing it at the back of the eye, down to a point on the retina.
  • The retina is protected by millions of light-sensitive receptors, called rods and cones. receptor contains pigment molecules, which change shape when light reaches them, causing an electrical message that passes through the optic nerve to the brain.
  • The back of the eye is covered by a layer of light-sensitive cells with a thickness of only fractions of one millimeter. When light photons strike the pigments within the cells, it causes a cascade of signals that travel through a series of different connections before transmitting them to the brain.
  • They pass first to the interneurons, then to the neurons known as ganglion cells. Such cells are cross-linked, capable of comparing neighboring signals, filtering out some of the information before forwarding it to the brain. That helps to enhance contrast and meaning. The neurons are moving over the back surface toward the optic nerve, relaying the information to the brain.
  • As the two optic nerves enter the brain, they cross over, coming together at a point known as the optic chiasm. Here, signals from the left side of both eyes are diverted to the left side of the brain, and vice versa, allowing the images from both eyes to be combined and compared.
  • Via the thalamus, the signals penetrate the brain, splitting the incoming information into two parts, one comprising color and imagery and the other movement and contrast. Then the signals pass back into the brain, and into the visual cortex. The cortex is laid out so that it resembles the rear of the retina, enabling the reconstruction of a detailed image.

Note

  • Each eye has 6 to 7 million cone cells, with one of three color-sensitive proteins known as opsins. Once light photons strike the opsins, they change form, causing a cascade that generates electrical signals, which transmits the messages to the brain in turn. Over half of our cone cells respond to red light, about a third to green light, and just 2% to blue light, giving us a vision centered on the yellow-green spectrum area. The vast majority of the human eye’s cone cells are found in the middle of the retina, at a location known as the fovea, containing only fractions of one millimeter. Light is focused on this level , providing at the center of our vision a clear, full-color image. 120 million rod cells dominate the majority of the retina, which sense light but not color.
  • Our eyes can only create two-dimensional images, but the brain is able to turn such flat images into a three-dimensional vision with a certain clever processing. Our eyes are located at a distance of about five centimeters (two inches), so each views the world from a slightly different viewpoint. The brain compares the two images, using the differences to establish the impression of profundity.

We see the world in wavelengths of red, green and blue, but most other species only see in yellow and brown. Some species of fish, reptiles and birds have four-color vision, and are able to see ultraviolet or infrared light too

The picture we see consists of light that is reflected from the objects we look at. This light reaches the eye through the cornea, at the front of the body, functioning like a shutter. It bends the light as the front portion of the eye is bent, making an upside down image on the retina.

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