The Human Eye

 The human eye.

The human eye is the most

valuable and sensitive sense organ and

it is a natural optical instrument the

eye is nearly spherical in shape with a

slight bulge in the front part and it

enables us to see the beautiful colorful

world around us let us discuss about the

important parts of the eye and the

functions.

 

Cornea the front part of the

eye is covered by transparent spherical

membrane called cornea light enters the

eye through Cornea, iris just behind the

cornea is a dark colored muscular

diaphragm which has a small circular

opening in the middle pupil.

 Pupil is a small circular opening of iris the pupil

appears black because no light is

reflected from it the dark center in the

middle of the iris the pupil determines

how much light is let into the eye

it changes sizes to accommodate for the

amount of light that is available the

iris regulates the light by justing the

size of the pupil let us see how iris

regulates and controls the amount of

light entering the eye when the

intensity of light is more or if it is a

bright source of light then the iris

makes the pupil to contract and as a

result the amount of light entering the

eye decreases when the intensity of

light is less or if the light is dim.

Then the iris dilates the pupil so that

more light can enter the eye islands the

islands is a convict land made of

transparent jelly-like proteinaceous

material the eye lens is hard at the

middle and gradually becomes soft

towards the outer edges the eye lens is

held in position by ciliary muscles the

ciliary muscles help in changing the

curvature and focal length of the

islands retina in the back surface of

the eyeball is called retina it is a

semi-transparent membrane which is

light-sensitive and is equivalent to the

screen of a camera the light-sensitive

receptors of the retina are called rods

and cones when light falls on these

receptors they send electrical signals

to the brain through the optic nerve the

space between the retina and islands is

filled with another fluid called

vitreous humour blind spot it is a spot

at which the optic nerve enters the eye

and is insensitive to light and hence

the name let us discuss about

Accommodation of the eye and power of

accommodation accommodation of the eye

the process by which the ciliary muscles

changed the focal length of an eye lens

to focus distant or near objects clearly

on the retina is called the

accommodation of the eye power of

accommodation the ability of the eye to

focus objects lying at different

distances is called the power of

accommodation of the eye how does an eye

focus objects at varying distances when

the ciliary muscles are relaxed the

islands becomes thin thus its focal

length increases and we see the distant

objects clearly when the ciliary muscles

are contract then the curvature of the

islands increases and the islands

becomes thick thus its focal length

decreases and we see the nearby objects

in brief it is adjustment of the focal

length of the eye lens which enables us

to focus on objects situated at

different distances least distance of

distinct vision near point near point or

least distance of distinct vision is a

point nearest to the eye at which an

object is visible distinctly for a

normal eye the least distance of

distinct vision is about 25 centimeters

however it varies with age of the person

for example for infants it is only 5 to

8 centimeter the far point of the eye

far point of the eye is a maximum

distance up to which the normal eye can

see things clearly it is infinity for a

normal eye cataract the crystalline lens

of people at old age becomes milky and

cloudy this condition is called cataract

this causes partial or complete loss of

vision it is possible to restore vision

through a cataract surgery range of

vision the distance between the near

point and the far point is called the

range of vision.