By – Dipanshu Nagar

HUMAN EYE The Key to Vision

INTRODUCTION

The human eye is one of the most valuable and sensitive sense organs.

It is like a camera, it captures images, accommodates them, and sends it to the brain which interprets it.

INDEXStructureFunctioningPower of AccommodationThe need of two eyesDefects of the eye

– Myopia and its correction– Hypermetropia and its correction– Presbyopia and its correction

Eye Donation

Structure of the Human EyeA Human Eye has the following parts : Aqueous humour Pupil Iris Cornea Retina Optic nerve Vitreous humour Ciliary muscles Crystalline lens

How the eye works

We can only see things when light gets reflected off the objects. This reflected light enters our eyes, forms an image and sends messages to the brain; the brain then interprets the image.

Probably the most important part of the eye is the lens, it bends the light rays so that they can be concentrated to form tiny, but clear and perfect images of the large objects. We will talk about the main parts of the eye in the next slide…

How the eye works• The Cornea - It is a round, transparent thin

membrane where light is refracted first. • The Sclera - The white part of the eye, it is a

protective layer on the eyeball.• Ciliary muscles - Helps to adjust the shape of

the lens.• Iris – It dilates or contracts the pupil and thus

control the amount of light falling on the retina. • The Lens – It is the elastic and transparent part

that refracts the light so that it falls on the retina.

How the eye works• The Vitreous Humor –it is the jelly-like texture that

is contained within the interior chamber, behind the lens

• The Retina - forms the entire curved inside of the eyeball and is lined with two types of light-sensitive cells, the rods (sensitive to light of low intensity but not to colors) and cones (sensitive to colors).

• The Optic Nerve - all the rods and cones are connected to the brain by a nerve and all these nerves form a thick cable called the optic nerve. This emerges from the back of the eye, moves through the skull and ends up inside the skull bone, beneath the brain near the pituitary gland.

Power of accommodation

The ability of the lens of the eye to adjust its focal length is called accommodation. However, the focal length of the lens cannot be reduced to a certain minimum limit. That is why we can see objects placed more than 25 cm from our eyes.

The need for two eyes

A human being has a horizontal view of 150° to extend it we have two eyes which give a combined view of 180°

Also, with only one eye, we can have only a 2D view while two eyes give a 3D view, providing the ability to detect faint objects.

Defects of the eye• Myopia

Myopia is also known as near sightedness. A person with this defect has a far point nearer than infinity.

Myopia is corrected by placing a concave lens before the eye.

Defects of the eye• Hypermetropia

Hypermetropia is also known as far-sightedness. A person with this defect can see distant object clearly, but cannot see nearby objects distinctly.

Hypermetropia is corrected by placing a convex lens before the eye.

Defects of the eye• Presbyopia

With the increasing age, the power of accommodation of our eyes usually decreases. As a result, some people suffer both Myopia and Hypermetropia.

Presbyopia is corrected by placing a bi-focal lens before the eyes. The upper part of this lens is a concave lens (Myopia) while the lower part is convex (Hypermetropia) lens.

Defects of the eye• Cataract

Sometimes, the crystalline lens of the eye becomes milky and cloudy with age, this condition is known as Cataract. It causes partial or complete loss of vision.

Cataract is removed with the help of a cataract surgery.

Eye donation

Do you know that our eyes can live even after our death?

We can light up a blind person’s life by donating our eyes after we die. About 35 million people in the world are blind and most of them can be cured with donated eyes.

“ We are lucky to have this gift of god, so why not pass it on to someone who

doesn’t have it !!”

THANK YOU !