All defination chapter - human eye
Answers
Answer:
It is a naturally occurring optical instrument. As you all know that we have a pair of eyes and its function is to enable us to see. Without it the whole world would have been a dark place for us.
Structure of eye
It is a spherical ball with a small bulge in the front part.
It is located in the eye socket.
It has two layers that cover it: scleroid and choroid.
Function of scleroid: It is the outermost covering that consists of white fibres and its function is to protect all parts of the eye.
Function of choroid: It is a grey membrane attached to choroid from inner side. Its function is to darken the eye from inside so that no internal reflection takes place.
Apart from these layers, it consists of :
Cornea
Iris
Pupil
Ciliary muscle
Lens
Retina
Blind spot
Optic nerve
Cornea:
It is the white part of the eye that allows light to enter.
It acts as a window to the world.
Iris:
It is colored part of the eye.
It holds the pupil and also adjust the size of pupil according to the intensity of light.
Pupil:
It is black in color and absorbs all the light rays falling on it.
It gets constricted when the intensity of light is high.
It gets expanded when the intensity of light is low.
Ciliary muscles
They hold the lens.
They adjust the focal length of the lens.
Convex lens
A cellular structure resembling convex lens (diverging lens).
Retina :
It is the screen of an eye where image is formed.
It consists of two types of cells:
Cone cells: those cells which respond to colours.
Rod cells: those cells which respond to the intensity of light.
Yellow spot:
A point on the retina where the most clear image is formed.
Blind spot: It is that point on the retina where no image is formed.
Optic nerve: A nerve that connects the eye to the brain.
The fluid which is present between cornea and lens is called aqueous humour.
Function : It is a watery fluid present in the interior part of the eye and its function is to protect the exterior part of the eye from collapsing when there is a sudden change in the atmospheric pressure. Also, it is the fluid that flows out from the eye when we wink our eyes. So, it washes the eye and also keeps it moist.
The fluid is present between lens and retina and is called vitreous humor.
Function: It is a dense jelly - like fluid present in the posterior part of the eye and its function is to protect the posterior part of the eye from collapsing when there is a sudden change in the atmospheric pressure. It also helps in focusing the image clearly on the retina.
Adjustment of the size of the pupil according to the intensity of light: When we are exposed to bright light the iris constricts the pupil partially or we can say that the pupil shortens so that the right amount of light enters and a clear image is formed. Whereas in a dark room, Pupil expands itself to gather more light in order to obtain a clear image.
Accommodation of eye: It is the ability of the eye lens to adjust its focal length so that a clear image is formed on the retina that can be easily recognized by our brain.
In case of far off objects.
In order to see a far off object, our ciliary muscles, lens and focal length undergo a change i.e. the ciliary muscles relax, lens become thin and elongated and focal length increases.
In case of nearby objects.
In order to see nearby objects, focal length of the lens and ciliary muscles undergo a change.
ciliary muscles contract, lens become thick and short and the focal length decreases.
Answer:
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Human eye, in humans, specialized sense organ capable of receiving visual images, which are then carried to the brain. cross section of the human eye. A horizontal cross section of the human eye, showing the major parts of the eye, including the protective covering of the cornea over the front of the eye.
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