Human eye- the eye

Question 1

the human eye is like a camera. elucidate

Answer 1

the human eye and the camera have many similarties.
i) both have bi convex lens. so the image formed is real and inverted.
ii)the shutter in the camera is like the eyelid of our eyes,
iii) the retina of our eyes can be compared to the film in the camera.
iv)both our eye and camera work in the presence of light,

Question 2

what is the main difference between camera and our eye

Answer 2

in the camera, the power and focal length of the lens is fixed, the image distance varies according to the object distance. the eye lens, however, can change its power and focal length according the object distance with the help of the ciliary muscles. the image distance, that is the distance between the retina and eye lens, remains constant

Question 3

what is the function of the sclerotic and choroids

Answer 3

it protects the internal parts of the eye.

Question 4

what is the choroid

Answer 4

it is the membrane attatched to the sclerotic. It helps on darkening the eye from the inside and prevents any internal reflection.

Question 5

what is the cornea what is its function

Answer 5

the cornea is a thin transparent membrane which forms a bulging portion in the front surface of the eyeball. It allows light to enter the eye. Most of the refraction of light rays entering the eye occurs on the outer surface of the cornea

Question 6

comment on the shape and size of the eyeball

Answer 6

the human eyeball is almost spherical in shape having a diamater of 2.3 cm

Question 7

describe the iris

Answer 7

iris is a dark muscular diaphragm having a tiny hole in the middle called the pupil. its function is to control the size of the iris.
imp:
iris has muscles and coloured pigments so the colour of the eye depends on the colour of these pigments

Question 8

what is the pupil

Answer 8

the pupil is a small hole in the iris which regulates and controls the amount of light entering the eye

Question 9

how does the iris and pupil work together

Answer 9

As the iris relaxes, the pupil becomes bigger allowing more light to enter the eye. When the iris contracts, the pupil becomes smaller allowing lesser light to enter. So the iris and the pupil together control the intensity of the light entering the eye.

Question 10

describe the eye lens

Answer 10

it is a crystalline bi convex lens made of transparent and flexible tissues. It forms real and inverted image on the retina. it also provides finer adjustment of the focal length reqired to focus objects at diffferent distances on the retina, it is composed of fibrous-jelly like material.

Question 11

what are the ciliary muscles

Answer 11

it is the ring of muscles which hold the lens in position. its function is the alter the focal length and power of the lens so that the objects at various distances can be focused clearly on the retina

Question 12

describe how the ciliary muscles achieve their function

Answer 12

when the object is at infinity (farthest point) the ciliary muscles are relaxed. The lens becomes thin and the focal length increases, power decreases.
when the object is at the near point that is 25cm the ciliary muscles contract. the lens becomes thick, the focal length decreases and the power of the lens increases

Question 13

describe the retina

Answer 13

the retina is a delicate membrane which has an enormous number of light sensitive cells. the retina receives the optical image of the object. The light sensitive cells get activiated upon illumination and generate electrical signals which are sent to the brain through the optic nerves

Question 14

what are found in the retina

Answer 14

the retina has a large number of roc cells and cone cells.
-cone cells are responsible for the colour of the image
-rod cells are responsible for the brightness/intensity fo the image

Question 15

what causes colour blindness

Answer 15

colour blindness is due the lack of a few cone cells. cone cells are blue,red and green coluorued

Question 16

what is the yellow spot

Answer 16

yellow spot is the centre of the retina which is extremely sensitive to light and gives a very clear image

Question 17

what is the blind spot

Answer 17

blind spot is the the region on the rretina where the optic nerve enters the eye ball. It is insensitive to light

Question 18

what is the optic nerve

Answer 18

the optic nerve carrues optical messages to the bran.

Question 19

what is the aqueous humour

Answer 19

it is the fluid filling the space between our cornea and the eye lens. it prevents the eyeball from collapsing

Question 20

what is viterous humour

Answer 20

it is the watery saline fluid that fills the space between the eye lens and the retina. It washes the eye and keeps the cornea moist.

Question 21

define accomodation

Answer 21

the ability of the eye to adjust its focal length by the action of ciliary muscles in such a way that objects placed at different distances from the eye are focused into a sharp focused image on the retina is called power of accommodation of eye

Question 22

define near point

Answer 22

The minimum distance, at which objects can be seen most distinctly without strain, is called the least distance of distinct vision of the eye. For a young adult with normal vision, the near point is about 25 cm.

Question 23

define far point

Answer 23

The farthest point up to which the eye can see objects clearly is called the far point of the eye. It is infinity for a normal eye.

Question 24

define range of vision

Answer 24

The distance between the near point and far point of an eye is known as range of vision. For normal eye, the range of vision is 25 cm to infinity.

Question 25

define power of accomodation

Answer 25

The power of accommodation of an eye is defined as maximum variation in the power of the eye lens.
maximum power of accomodation of a normal eye is 4D