Human Eye

Our eyes help us to see all the beautiful things around us

Let's study the structure and function of the eye

How does Our Eyes help us to see?

Our Eyes are based on principle of Refraction of Light

It acts like a camera and has a convex lens (called eye lens) and a screen called retina

Light enters eyes, get refracted from cornea and eye lens and forms image on the screen called retiina

The light sensitive cells on retina sends electrical signals to the brain via optical nerves

Brain interprets these signals and we are able to see the objects

What kind of Image is formed by eyelens on retina?

Since eye lens is convex lens

It forms an inverted real image of the object

Note - Though image formed is inverted, our brain interprets image as errect

What is Shape of Human Eye?

It is approximately spherical in shape

It has a diameter of 2.3 cm

What are Different Parts of Human Eye?

Cornea

Outermost layer is called Cornea

It is transparent

Most of refraction of Light Rays occur at the outer surface of Cornea

Iris

Behind the cornea, there is dark muscular structure

It is called iris

The colour of the iris of different people is different.

Some have brown eyes, some black, some blue

So, Iris gives color to the eye

Pupil

In iris,there is a small opening called pupil

Pupil Regulates amount of light entering Eyes

Note: Pupil is the hole in the middle of iris

Crystalline Lens

Behind the pupil, there is convex lens which is called crystalline lens or eye lens

The Lens forms inverted real image on screen at back of eye called retina

Note - Most of refraction of Light Rays occur at the outer surface of Cornea
The crystalline lens provides the finer adjustment of focal length so that image is formed on the retina

Aqueous Humour

It helps in changing shape of lens

This helps lens to focus

Retina

It is a delicate membrane (layer) on back of eye

Image is formed on the retina

Retina contains different light sensitive cells

These cells generate electric signals and transfer them to brain via optic nerve

Optical Nerve Cells (Light Sensitive Cells)

There are 2 types of cells

• Cones
  They are sensitive to bright light.they sense color
• Rods
  They are sensitive to dim light

Optic Nerve

Sensations felt by nerves are transmitted to the brain by optic nerve

Ciliary Muscle

It helps in changing shape of lens

This helps lens to focus

Vitreous Humour

The space between lens and retina is filled by a jelly like substance called Vitreous Humour

Function of Iris and Pupil

Iris regulates the amount of light entering the eye

In the day, the amount of light entering our eyes is large

So, the iris contracts the pupil to allow less light to enter

However

In the night , the amount of light entering our eyes is small

So, the iris expands the pupil to allow more light to enter

The Function of Iris and Pupil is explained here