Human eye- the eye Flashcards
the human eye is like a camera. elucidate
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,
what is the main difference between camera and our eye
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
what is the function of the sclerotic and choroids
it protects the internal parts of the eye.
what is the choroid
it is the membrane attatched to the sclerotic. It helps on darkening the eye from the inside and prevents any internal reflection.
what is the cornea what is its function
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
comment on the shape and size of the eyeball
the human eyeball is almost spherical in shape having a diamater of 2.3 cm
describe the iris
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
what is the pupil
the pupil is a small hole in the iris which regulates and controls the amount of light entering the eye
how does the iris and pupil work together
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.
describe the eye lens
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.
what are the ciliary muscles
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
describe how the ciliary muscles achieve their function
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
describe the retina
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
what are found in the retina
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
what causes colour blindness
colour blindness is due the lack of a few cone cells. cone cells are blue,red and green coluorued
what is the yellow spot
yellow spot is the centre of the retina which is extremely sensitive to light and gives a very clear image
what is the blind spot
blind spot is the the region on the rretina where the optic nerve enters the eye ball. It is insensitive to light
what is the optic nerve
the optic nerve carrues optical messages to the bran.
what is the aqueous humour
it is the fluid filling the space between our cornea and the eye lens. it prevents the eyeball from collapsing
what is viterous humour
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.
define accomodation
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
define near point
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.
define far point
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.
define range of vision
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.
define power of accomodation
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
