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Explain the structure of an eye with a diagram.

The Shape of the eye is roughly spherical with an average diameter of around 2.3 cm. The outer part of the eye is quite tough and white in colour. This white part of the eye is known as sclera.The transparent, front outer covering of the eye is known as the cornea. Behind the cornea, there is a colored membrane known as the iris. It regulates the amount of light entering the eye. It also gives colour to the eye. In the iris, there is a variable sized, black circular opening known as the pupil. Its size is controlled by the iris. It appears to be black in colour because most of the light entering it is absorbed by the tissues, which are present in the pupil.

The size of the pupil depends on the brightness of light. It opens and closes in order to regulate and control the amount of light entering the eye. When we enter a dimly lit room, it takes the iris some time to expand the pupil to allow more light to enter the eye. For this reason, it takes us a few seconds to clearly see objects in a dimly lit room


 

 

 

 

 

 

Behind the pupil there is a lens which is thicker at the centre. It is made up of living cells. Two Ciliary muscles hold the lens within the eye-ball. The eye lens being convex in nature converges the light rays’ incident on it. Hence, it focuses the light falling on it on a thin layer of nerve cells called the retina. The retina is made up of a large number of nerve cells. Light falling on these nerve cells stimulate two kinds of sensitive cells known as cones and rods. Rods are sensitive to low light levels. Cones are sensitive to bright light, but they sense colours. Sensation felt by them is transmitted to the brain in the form of electrical signals through the optic nerve. This allows us to see.

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Structures of the Eye

The structures of the eye include:

  • The pupil, which is the opening in the colored part of the eye (iris). The iris controls the size of the pupil in response to light outside the eye so that the proper amount of light is let into the eye.
  • The lens, which is located behind the iris and is normally clear. Light passes through the pupil to the lens. Small muscles attached to the lens can change its shape. Tightening or relaxing these muscles causes the lens to change shape, allowing the eyes to focus on near or far objects.
  • Vitreous gel (also called vitreous humor), which is a thick liquid that fills the eye. It helps the eyeball maintain its shape.
  • The retina, which is a thin nerve membrane that detects light entering the eye. Nerve cells in the retina send signals of what the eye sees along the optic nerve to the brain.
  • The optic nerve, which is the nerve at the back of the eye that carries visual information from the eye to the brain.
  • The macula, which is near the center of the retina at the back of the eyeball. The macula provides the sharp, detailed, central vision a person uses for focusing on what is directly in the line of sight.
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Structures of the Eye

The structures of the eye include:

  • The pupil, which is the opening in the colored part of the eye (iris). The iris controls the size of the pupil in response to light outside the eye so that the proper amount of light is let into the eye.
  • The lens, which is located behind the iris and is normally clear. Light passes through the pupil to the lens. Small muscles attached to the lens can change its shape. Tightening or relaxing these muscles causes the lens to change shape, allowing the eyes to focus on near or far objects.
  • Vitreous gel (also called vitreous humor), which is a thick liquid that fills the eye. It helps the eyeball maintain its shape.
  • The retina, which is a thin nerve membrane that detects light entering the eye. Nerve cells in the retina send signals of what the eye sees along the optic nerve to the brain.
  • The optic nerve, which is the nerve at the back of the eye that carries visual information from the eye to the brain.
  • The macula, which is near the center of the retina at the back of the eyeball. The macula provides the sharp, detailed, central vision a person uses for focusing on what is directly in the line of sight.
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Structures of the Eye

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