The Various parts of eye and their functions
1. Cornea : It is a thin membrane through which light enters. It forms the
transparent bulge on the front of eyeball. Most of the refraction occurs at the
outer surface of the cornea.
2. Eyeball : it is approximately spherical in shape, with a diameter of about 2.3cm.
3. Iris : It is a dark muscular diaphragm that controls the size of pupil. It is behind the cornea.
4. Pupil : It regulates and control the amount of light entering the eye. It is the black opening between aqueous humour & lens.
5. Crystalline eye lens : Provide the focussed real & inverted image of the object on the retina. It is composed of a fibrous, jelly like material. This is convex lens that converges light at retina.
6. Ciliary muscles : It helps to change the curvature of eyelens and hence changes its focal length so that we can see the object clearly placed at different positon.
7. Retina : Thin membrane with large no. of sensitive cells.
8. When image formed at retina, light sensitive cells gets activated and generate electrical signal. These signals are sent to brain via optic nerue. Brain analyse these signals after which we perceive object as they are.
How pupil works ?
Here the pupil of an eye provide a variable aperture, whose size is controlled by iris a) When the light is bright : Iris contracts the pupil, so that less light enters the eye.
b) When the light is din : Iris expand the pupil, so that more light enters the eye. Pupil open completely, when iris is relaxed
Persistence of Vision : It is the time for which the sensation of an object continue th in the eye. It is about 1/16 of a second.
Power of Accommodation : The ability of eye lens to adjust it focal length is called accommodation with the help of ciliary muscles.
DEFECTS OF EYE:
1. CATARACT : The image can not be seen distinctly because eye lens become milky and cloudy. This condition is known as cataract, it can cause complete or partial loss of vision. This can be corrected by surgical removal of extra growth (cataract surgery)
2. Myopia : (Near Sightedness) Aperson can see nearby object clearly, but cannot see distant object distinctly. Image formed in front of the retina. It is corrected by using a Concave Lens of appropriate power.
(3) Hypermetropia (Far - Sightedness) – Aperson cannot see nearby object clearly, but can see distant object distinctly. Image formed at a point behind the retina. It is corrected by using a Convex Lens of appropriate power.
4. Presbyopia As we become old, the power of accommodation of the eye usually decreases, the near point gradually recedes away. This defect is called Presbyopia. Person may suffer from both myopia and hypermetropia.
Correction- Using of Bifocal lens with appropriate power.
UNDERSTANDING THE EYE :
The eye functions in a similar way to a sophisticated camera. Light from an object will first pass through the cornea (the transparent dome at the front of the eye), which is the major focusing element of the eye and begins the process of bending (or refracting) the light rays. It then enters the front of the eye, which is filled with clear fluid called the aqueous humour; passes through the pupil, the round opening in the middle of the coloured iris until it reaches the lens, the fine focusing element of the eye. The lens completes the work started by the cornea by bending (refracting) the light rays so they focus at a single point on the retina. Behind the lens and in front of the retina is the main cavity of the eyeball, filled with a clear gel called the vitreous humour. The retina is made up of nerve tissue and is fed by a network of blood vessels (the choroid) supplying it with a constant source of oxygen and nutrients. Light falling on the retina causes impulses to be transmitted along the optic nerve and so that the brain can assemble a "clear picture". However, this will only occur if all the various components of the eye are in working order.
The lens is encased within a bag known as the capsule, which is suspended by delicate fibres called zonules. These zonules are the ligaments attaching the lens to the circular muscle ring, the ciliary body. Contraction of this muscle varies the tension on the lens capsule and allows the lens to become fatter so that the eye can change its focus for near vision. This process is called accommodation and allows the eye to see for reading. With advancing age the lens becomes harder and the ciliary muscle weaker and the ability of the eye to change its focus for near vision reduces. This is called presbyopia and is the reason that most people will require reading glasses after the age of 50.
2. Eyeball : it is approximately spherical in shape, with a diameter of about 2.3cm.
3. Iris : It is a dark muscular diaphragm that controls the size of pupil. It is behind the cornea.
4. Pupil : It regulates and control the amount of light entering the eye. It is the black opening between aqueous humour & lens.
5. Crystalline eye lens : Provide the focussed real & inverted image of the object on the retina. It is composed of a fibrous, jelly like material. This is convex lens that converges light at retina.
6. Ciliary muscles : It helps to change the curvature of eyelens and hence changes its focal length so that we can see the object clearly placed at different positon.
7. Retina : Thin membrane with large no. of sensitive cells.
8. When image formed at retina, light sensitive cells gets activated and generate electrical signal. These signals are sent to brain via optic nerue. Brain analyse these signals after which we perceive object as they are.
How pupil works ?
Here the pupil of an eye provide a variable aperture, whose size is controlled by iris a) When the light is bright : Iris contracts the pupil, so that less light enters the eye.
b) When the light is din : Iris expand the pupil, so that more light enters the eye. Pupil open completely, when iris is relaxed
Persistence of Vision : It is the time for which the sensation of an object continue th in the eye. It is about 1/16 of a second.
Power of Accommodation : The ability of eye lens to adjust it focal length is called accommodation with the help of ciliary muscles.
DEFECTS OF EYE:
1. CATARACT : The image can not be seen distinctly because eye lens become milky and cloudy. This condition is known as cataract, it can cause complete or partial loss of vision. This can be corrected by surgical removal of extra growth (cataract surgery)
2. Myopia : (Near Sightedness) Aperson can see nearby object clearly, but cannot see distant object distinctly. Image formed in front of the retina. It is corrected by using a Concave Lens of appropriate power.
(3) Hypermetropia (Far - Sightedness) – Aperson cannot see nearby object clearly, but can see distant object distinctly. Image formed at a point behind the retina. It is corrected by using a Convex Lens of appropriate power.
4. Presbyopia As we become old, the power of accommodation of the eye usually decreases, the near point gradually recedes away. This defect is called Presbyopia. Person may suffer from both myopia and hypermetropia.
Correction- Using of Bifocal lens with appropriate power.
UNDERSTANDING THE EYE :
The eye functions in a similar way to a sophisticated camera. Light from an object will first pass through the cornea (the transparent dome at the front of the eye), which is the major focusing element of the eye and begins the process of bending (or refracting) the light rays. It then enters the front of the eye, which is filled with clear fluid called the aqueous humour; passes through the pupil, the round opening in the middle of the coloured iris until it reaches the lens, the fine focusing element of the eye. The lens completes the work started by the cornea by bending (refracting) the light rays so they focus at a single point on the retina. Behind the lens and in front of the retina is the main cavity of the eyeball, filled with a clear gel called the vitreous humour. The retina is made up of nerve tissue and is fed by a network of blood vessels (the choroid) supplying it with a constant source of oxygen and nutrients. Light falling on the retina causes impulses to be transmitted along the optic nerve and so that the brain can assemble a "clear picture". However, this will only occur if all the various components of the eye are in working order.
The lens is encased within a bag known as the capsule, which is suspended by delicate fibres called zonules. These zonules are the ligaments attaching the lens to the circular muscle ring, the ciliary body. Contraction of this muscle varies the tension on the lens capsule and allows the lens to become fatter so that the eye can change its focus for near vision. This process is called accommodation and allows the eye to see for reading. With advancing age the lens becomes harder and the ciliary muscle weaker and the ability of the eye to change its focus for near vision reduces. This is called presbyopia and is the reason that most people will require reading glasses after the age of 50.
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