Powerpoint presentationon

human eyeand

it’s defect

FA – 3

the human eye The human eye is one of the most valuable and

sensitive sense organs. It enables us to see the wonderful world and the colours around us.

We can identify objects to some extent by their smell, taste, sound they make or by touch. But we can’t identify the colours when our eyes are closed.

The human eye works on the principle of Refraction Of Light .

Main part of human eye are:- Cornea, Iris, Pupil, Ciliary muscles, Eye lens, Retina and Optic nerve.

The eyeball is approximately sphericle in shape with a daimeter of about 2.3cm .

Structure of human eye

RetinaCornea

PupilIris

Lens

Optic nerve

Ciliary musclesVitreous humour

Aqueoushumour

Parts And Functions Of The Human EyeCORNEA :-It is a thin membrane through which light enters the eye. It forms the transparent bulge on the front surface of the eye. CORNEA

IRIS

IRIS :- Iris is a dark muscular daiphragm that controls the size of the pupil.

CILIARY MUSCLES:- Ciliary Muscles change the thickness of eye lens by focusing.

CILIARY MUSCLES

DILATED PUPIL

CONSTRICTED PUPIL

PUPIL:- Pupil is the hole in the middle of Iris. The pupil regulates and controls the amount of light entering the eye.

EYE LENS:- The eye lens is a covex lens made of transparent and flexible material (protien). It forms an inverted real image of the object on the retina .

EYE LENS transplant

RETINA:- The retina is a delicate membrane having enormous number of Light-Sensitive cells on which the image is formed. The two types of light-sensitive cells are – ROD CELLS and CONE CELLS .

RETINA

ROD CELLS

CONE CELLS

OPTIC NERVE :- Optic Nerve convey the signal which are generated by Light-Sensitive cell to the brain .

OPTIC NERVESCLERA :- Sclera is the white part of the eyeball. It helps in the attachment. Sclera is a tough white skin (made of tissue) that covers all of the eyeball except the cornea

SCLERA

POWER OF ACCOMmODATION The eye lens is composed of fibrous,

jelly-like material. Its curvature can be modified to some

extent by the ciliary muscles. The change in the curvature of the eye

lens can thus change its Focal lenght. The ability of the eye lens to adjust

its focal lenght is called accommodation.

When the muscles are relaxed, the lens becomes thin. Thus its focal lenght increases.

When you are looking at objects closer to the eye, the ciliary muscles contract. This increase the curvature of the eye lens and the focal lenght lens decreases.

Power of Accommodation

WORKING OF THE EYE

WORKING OF THE EYE The light rays coming from the object kept infront

of us enter through the Cornea of the eye, pass through the pupil of the eye and fall on the eye-lens.

The eye-lens is a convex lens, so it converges the light rays and produces a real and inverted image of the object on the retina.

The retina has a large number of light-sensitive cells. When the image falls on the retina then these light-sensitive cells get activated and generate electricle signals.

The image formed on the retina is conveyed to the brain by the optic nerve and gives rise to the sensation of vision.

DEFECTS OF VISION THEIR CORRECTION Sometimes, the eye may gradually lose

its power of accommodation. The person cannot see the objects

distinctly and comfortably. The vision becomes blurred due to the refractive defects of the eye.

There are mainly three common refractive defects of vision. These are :-

a) Myopia or near-sightedness.b) Hypermetropia or far-sightedness.c) Presbyopia.

MYOPIA :- Myopia is also known as near-sightedness. A person

with myopia can see nearby objects clearly but cannot see distant object distinctly.

In a myopic eye, the image of a distant object is formed infront of the retina and not at retina itself.

This defect may arise due to :-a) Excessive curvature of the eye lens.b) Elongation of the eyeball. This defect can be corrected by using concave lens

of suitable power. A concave lens of suitable power will bring the image

back on to the retina and thus the defect is corrected.

HYPERMETROPIA :- Hypermetropia is also known as far-sightedness. A

person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.

The near point, for the person, is farther away from the normal near point (25 cm).

As a result, the light rays from a closeby object are focussed at a point behind the retina.

This defect arises either because :-a) the focal lenght of the eye lens is too long.b) the eyeball has become too small. This defect can be corrected by using a convex lens of

suitable power. Eye-glasseswith converging lenses provide the

additional focussing power required for forming the image.

CORRECTION OF HYPERMETROPIA

Normal eye

Hypermetropic Eye

Light Rays Focussed on the retina.

Focussed beyond the retina.

Converging (convex) lens

Corrected eye

Makes light rays converge slightly.

PRESBYOPIA:-The power of accommodation of the eye usually decreases with ageing. For most people, the near point gradually recedes awayThey find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia.

Presbyopia in simple words is a type of hypermetropia which occurs in old age.

PRESBYOPIA:-It arises due to the gradual weakening of the ciliary muscles and diminishing flexibilityof the eye lens.A person may also suffer from both Myopia and Hypermetropia. Such people often require bi-focal lenses.A common type of bi-focal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision.

Human eye is one of the both valuable and sensitive sense organ which work on refraction of light and enables us to see the wonderful world.

summary

The parts of human eye are :- Cornea, Iris, Pupil, Ciliary Muscles, Eye lens, Retina and Optic nerve.

The ability of eyelens to adjustits focal lenght is called accommodation.

Light enters through the Cornea, of eye, passes through the Pupil, falls on the Eye lens which converges the light to form an Real and Inverted image on Retina, which contains the light sensitive cells. That generates electrical signals which are sent to the brain via optic nerve.

summary

GROUP MEMBERS NAME ROLL no.1. Md.irshad 522. Arko probho chattopadhyay 223. Dixita sur 244. Susmita saha 225. Bibhash dey 166. Samrat bhattacharjee 537. Harshita goswami 14

THANK

YOU