Question

Explain the structure and functioning of the human eye. How are we able to see nearby as well as distant objects

Answer 1

Eye:

1. The eye is the most important organ which helps us to view different objects.
2. It is like a camera, it forms an image on a light-sensitive screen called the retina.

Structure of the eye:

1. The external structure of the eyes are the sclera, conjunctiva, cornea, iris and pupil.
2. The internal structure includes lens, retina, optic nerve, aqueous humour and vitreous humour.
3. Optic nerve: Located posteriorly in the eye and they basically carry nerve impulses from the eye to the brain for perception.
4. Retina: It is present as the innermost layer in the eye. It is a photosensitive layer and it converts the image into electrical nerve impulses for visual reception in the brain.
5. Sclera: It is made up of dense connective tissue and is the visible outer portion. It helps in the protection of the inner layer.
6. Conjunctiva: It lines the sclera. It keeps our eyes moist by secreting tears and mucus.
7. Cornea: It covers the iris and the pupil. The refraction of light is the main function.
8. Iris: It is the pigmented coloured portion which is visible externally. The main function is to adjust the size of the pupil.
9. Pupil: It acts like camera focus and allows light to enter. It gets focused on the retina.
10. Lens: It is the transparent, biconvex lens of an eye. The cornea along with the lens helps in the refraction of light.
11. Aqueous humour: It is present between the cornea and the lens. It is a watery fluid-like substance. It provides nourishment to the eye and keeps it inflated.
12. Vitreous humour: It is present between the lens and the retina. It is a transparent jelly-like substance. It also provides protection to the eye and maintains its spherical shape.

Ability to see:

1. The process by which particular muscles known as ciliary muscles act to shift the focal length of the eyes so that the image is clearly produced on the retina is known as accommodation of the eye.
2. A normal person's accommodation power is roughly 4 dioptres.
3. The retina has numerous light-sensitive cells(rods and cones) which generate nerve impulses that are sent to the visual cortex for analyzing and representation in its proper form.
4. Power of accommodation is said as the ability of the eye lens to adjust its focal length, to clearly focus rays coming from distant as well as near objects on the retina.