Question

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“ Structure of Eye”

Explain
Diagram and explanation
Proper

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Answer 1

$\textbf{The Human Eye }$:

Human eye is the most important organ. It is used to see the beautiful nature and the natural phenomena. The human eye works on the refraction of light through a natural convex lens made of transparent living material and enable us to see things around us.

$\textbf{The main parts of human eye are }$:

Cornea, Iris, Pupil, Ciliary muscles, eye lens, retina and optic nerves.

1. $\textbf{Cornea}$:

It is transparent part of eye and allow the light to enter in the eyes, it is the outermost part of the eye.

2. $\textbf{Iris}$:

It is a circular diaphragm having a hole in it's centre. This hole is called $\textbf{pupil}$. The circular diapragm has muscles and coloured pigments. The colour of an eye depends on the colour of these pigments. The function of iris is to control the amount of light entering the eye through the pupil. The pupil becomes small when bright light falls on the eye but it becomes wide when there is dim light.

3. $\textbf{Eye lens }$:

The eye lens is a crystalline double convex lens and made of transparent and flexible tissues. It is behind the pupil and help them by the muscles called ciliary muscles. It focuses the images of objects on the retina of the eye.

4.$\textbf{Ciliary Muscles }$:

These muscles hold the eye lens in position. It controls the focal length of eye lens. When these muscles contracts the focal length of the lens increases when they expands they exerts pressure on the lens and decreases focal length.

5. $\textbf{Retina}$:

It acts as a screen to obtain the image of object. It contains number of cells in the form of rods and cones which are sensitive towards light. These cells convert light energy to into nerve impulses or signals.

6. $\textbf{ Optic Nerves }$:

Optic nerve is found by the nerve fibres coming from the retina. It transfers nerve impulses to the brain.

$\textbf{Working of the eye }$:

When will look towards an object light from the object enters the pupil of the eye and falls on the eyelens. The lens forms a real and inverted image on the retina of the eye. The retina of the eye contains special cells in the shape of rods and cones. These cells convert light energy into electrical signals. These electrical signals carried to the brain through the optic nerves.

Answer 2

$\huge\underline\mathfrak\blue{Human\:Eye-}$

Eyes are one of the most valuable and sensitive sense organs. Eye can be viewed by its vertical section.

Location : Eyes are located in the orbits of skull.

Size : Eyeball is approximately spherical in shape, its diameter is about 2.3 cm.

Structure : An eye has three layers and two chambers.

Layers : An eye has three coats.

a). Fibrous coat :

$\leadsto$ It is thick and tough. It has two distinct but unequal regions.

• $\bold\pink{Sclera-}$ It forms posterior $\frac{5}{6}$th of fibrous coat. It is present in the orbit, opaque in nature and bluish - white in colour. To this layer, eye muscles are attached which move the eyeball. This layer maintains the form of eyeball and protects the eyeball too.

• $\bold\pink{Cornea-}$ It is anterior $\frac{1}{6}$th portion of fibrous layer. It is transparent and remains bulged outward. It refracts the light rays towards the lens of eye.

b). Vascular coat :

$\leadsto$ It lies below the fibrous coat. It shows three regions.

• $\bold\pink{Choroid-}$ It lies below and in contact with sclera. It contains abundant blood vessels and pigment cells. It is dark brown in colour. Its blood vessels nourishes the retina and sclera.

• $\bold\pink{Ciliary\:body-}$ It is thickened portion of choroid in anterior portion, towards the cornea. It contains ciliary muscles which help in its contractions and relaxations. Inner surface of ciliary body is having radiating folds - ciliary processes. To these there are attached firm and elastic ligamentous structures - the suspensory ligaments. These ligaments keep the eye lens in its position.

• $\bold\pink{Iris-}$ It is a very thin, coloured and diaphragm like portion of vascular coat. This is having an aperture in its middle. It is called the pupil. It controls the size of pupil. So the English are not complete in structure but are perforated. Iris contains muscles of contractions and dilations. Due 2D types of muscles it can contract and dilate, making the size of pupil smaller and wider respectively. Iris provides characteristic colour to the eye ( like - greenish blue, grey, brown etc )

• $\bold\pink{Retina-}$ It is also called light sensitive layer. it lies in the inermost portion of eyeball, below the vascular coat. In front of eye lens, the retina has a point of most distinct vision. It is called the yellow spot, it contains only cone cells. There is another point on it, where vision power is zero because of its insensitiveness to light. It is called the blind spot. Retina is also having parts over the ciliary body and iris.

• $\bold\pink{Rod\:cells-}$ These are helpful in dim light vision. These cells make a blurred image of any object.

• $\bold\pink{Cone\:cells-}$ These are helpful in seeing in bright light. These are also used to perceive the basic colours ( red, green and blue )

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Eye lens : Eye lens is a double convex lens. It is a solid but elastic body. It is covered by thin, elastic and transparent membrane - the lens capsule. It is made up of transparent and flexible tissues. It remains in its position by suspensory ligaments. Suspensory ligaments and ciliary body can change the focal length of eye lens according to the distances of objects. Eye lens lies just behind the pupil. The light rays falling on It are refracted to the yellow spot.

Conjunctiva : Cornea and and small part of exposed sclera are covered by a thin transparent membrane - the conjunctiva. It remains attached with eye lids. Sometimes it is inflamed making eyes - pinkish - known as pink of eyes.

Optic nerve : From each eye, from its posterior portion, one nerve arises which carries the Informations of vision to the visual areas of brain.

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$\orange{\boxed{\boxed{\pink{\underline{\underline{\red{Functioning\:of\:eye-}}}}}}}$

Functioning contains two parts -

★ Focusing part : In this, the image of object is made at retina. In this function, conjunctiva, cornea, aqueous humour and lens help. Maximum refraction is caused by cornea which brings the image approximately on retina. Lens helps in fine adjustment and brings the image at sharp focus.

★ Receptor part : It involves retina. The image formed on retina is inverted, smaller and real. This formed image, activates the light sensitive cells of retina. Activated light cells standard electrical signals ( also called sensory or nerve impulse ). These signals are carried to visual areas in the brain via optic nerves. The brain interprets and analyses these signals. Finally, it processes the information, in such a way that we can perceive the objects as they are. It means we can see the objects upright with their natives characteristics.