The human eye is an essential part of our body. It is also one of the most complex sensory organs that animals and humans have. Eyes allow us to visualise things. One of the basic functions of eyes is to helps humans and animal with light perception, depth perception and identifying colours. Did you know that the camera was invented based on the structure and functionality of the human eye? The sense organs in our eyes are allow us to see objects when an external light enters them. Understanding the human eye is very interesting and amazing. You can also learn how the camera actually works. 

Our eyes function with the help of the refraction of light that passes through a natural convex lens, which is made of transparent living material. It enables us to see objects in our surroundings. The major parts of the human eye are: Cornea, Iris, Pupil, Eye lens, Retina Ciliary muscles, and the Optic nerve. 

Structure of The Eye

Cornea: The front part of our eye is the Cornea. the cornea is made up of a transparent substance and is protruding outwards. The outer layes of cornea is in convex shape. The light coming from objects enters our eye through the cornea.

Iris: Behind the cornea is the Iris. It is a coloured diaphragm, is coloured, flat, and a ring-shaped membrane behind the cornea.

Pupil: There is a tiny hole in the midst of the iris which is known as the pupil of the eye. The pupil appears to be black because no light can be reflected from it.

The lens of the eyes is a convex and made of a transparent, soft and elastic jelly-like material composed of proteins. Since it is flexible, the lens are able to change their shape, turn thick or thin in order to focus proper light on to the retina. The lens are held in place by the suspensory ligaments. One end of suspensory ligaments is joined to the lens and the other end is attached to the ciliary muscles.

Ciliary muscles: Ciliary muscles can change the thickness of he lens while focusing on something. The focal length of the lens and its converging power can be altered by altering the shape of the lens by the action of ciliary muscles. The focal length of the convex lens inside the eye can also be altered by the action of ciliary muscles.

Retina: The screen-line structure on which an image of the object is formed in the known as the retina. The retina is located behind the lens and at the extreme backside of the eye. It is a very delicate membrane with a large number of light-sensitive cells known as rods and cones. These cells respond to the intensity of colour and light of objects by producing electrical signals.

Blind Spot: There is a spot at the juncture of the optic nerve and retina, there are no ri=ods or cones (light-sensitive cells) due to which, no vision or image-building is possible at that spot. This spot is know as the blind spot. A blind spot can be said to be a tiny portion of the retina which is insensitive to light and where the optic nerve leaves the eye.

Eye Lid: In front of the eye the eye lid. It is  is the shutter of our eyes. When the eye lid is open, light can enter the eye but when eye-lid is closed, no light can enter.

Aqueous Humour: The gap between the cornea and lens is filled with a thick watery liquid known as the aqueous humour. The space between retina and lens is filled with a transparent jelly-like liquid known as the vitreous humour. It supports the back of the eye.

How to Eye Works

(1) The light rays coming from an object placed in front of us enter our eyes through the cornea, then pass through the pupil and fall on the lens.

(2) The lens of our eyes are convex in shape, and thus converges the incoming light rays and generates a real and inverted image of the object on our retina.

(3) The image thus formed on the retina is communicated to our brain by the optic nerves. this gives rise to the sense of vision. The retina has a large number of cells that are sensitive to light.

(4) When the image comes in contact with the retina, the light-sensitive cells get activated and produce electrical signals. The retina then sends these electrical signals to the brain through the optic nerve that gives the sensation of vision. Even though the image created on the retina is inverted, our brain interprets the image as an erect object.y

Function of Iris & Pupil

The iris monitors and manages the amount of light that enters our eyes. The iris adjusts the size of the pupil automatically and accordingly to the intensity of light received by our eye. If the intensity of the light coming in the eye is high, then the iris contracts the pupil, making the pupil small and decreases the amount of light coming in the eye.

If the intenstiy of the light coming in the eye is low like in a darkness, the iris expands the pupil so that more light can enter the eyes. The iris controls dilation and contraction of the pupil depending on the extend of light received by the eye. If the amount of the external light is less, then the pupils expand to bring in more light. If exernal intensity of light is high, the pupil contracts so that lesser light enters the eye. This adjustment of the size of pupil takes a few moments.

(1) As we enter a darkened room from a brightly lit space, we cannot see our surroundings clearly at first. After a few moments, our vision adjusts and we can see the surroundings clearly. When we are out under the sunlight, the size pupil of our eye is small. Thus, when we enter a dark place, very little light is able to enter our eye and thus we cannot see well.

(2) Inversely, when we enter a space with bright sunlight or switch on a bright light after coming from a dark room, we feel expansion of our eyes. This happens due to the fact that when in a dark location, the pupil of our eye is bigger. hence, as we go out from a dark room into brightness, a large intensity of light enters our eyes and our pupils contract so that less light then can enter our eyes.

What are Rods and Cones in the Eye?

The retina of our eye have innumerable cells that are sensitive to light. There are basically two types of these light-sensitive cells on the retina known as rods and cones.

(1) Rods: As the name suggests, they are rod-shaped cells located inside the retina. they are sensitive to dim light. We can see our surroundings in a dark room to some extent thanks to the presence of rod cells in the retina of our eyes. Nocturnal animals, i.e. the animals that sleep during the day time and come out during night time, like the owl, have a large number of rod cells in their eye retina. this helps them see clearly in the darkness. Rod cells of the do not send any information about the colour of the object to the brain.

(2) Cones:  As the name suggests, they are cone-shaped cells located in the retina of an eye. They are sensitive to light. Unlike the rod cells, the cone cells respond to colours.

Functions of Major Eye Components

Below are the functions performed by the major eye components:

S.No.	Human Eye Part	Functions
1.	Pupil	Opens and closes to manage and control the intensity of light entering the eye.
2.	Iris	Similar to the aperture of a camera, it controls light level.
3.	Sclera	Shields the outer coat.
4.	Cornea	A thin membrane that makes up for 67% of the eye’s focusing power.
5.	Crystalline lens	Helps to centre light on to the retina.
6.	Conjunctive	Covers the outer visible surface of the eye.
7.	Aqueous humour	Extends  power to the Cornea.
8.	Vitreous humour	Gives the eye its form and shape.
9.	Retina	Captures the light rays centred by the lens and transmits impulses to the brain through the optic nerve.
10.	Optic nerve	Sends electrical signals to the brain.
11.	Ciliary muscles	Contracts and dilates to allow changing of the lens shape for focusing.

We hope this article on The Eye helps you understand the structure and functioning of our eyes. For more informative articles, keep visiting Embibe.