human eye

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CLASS : VIII – B SUBJECT: SCIENCE CHAPTER 16 : LIGHT TOPIC: EYE - STRUCTURE AND WORKING: 

CLASS : VIII – B SUBJECT: SCIENCE CHAPTER 16 : LIGHT TOPIC: EYE - STRUCTURE AND WORKING

STRUCTURE OF HUMAN EYE : 

STRUCTURE OF HUMAN EYE

PARTS OF HUMAN EYE : 

PARTS OF HUMAN EYE 1 . CORNEA - The transparent front part of eye through which the light enters. 2 . IRIS - There is a dark muscular structure behind the cornea. It controls the size of pupil. 3 . PUPIL -In the iris there is a small opening called pupil. It regulates and controls the amount of light entering the eye. 4 . CILIARY MUSCLE - Eye lens is attached to ciliary muscle.

5. EYE LENS- It is a convex lens. It focuses the light on retina . It forms real and inverted image of object On retina. 6. RETINA- A screen on which an image is formed on the eye. It is behind the lens. It contains several nerve cells. It consists of light sensitive cells. 7. OPTIC NERVE- The retina contains several nerve cells. Sensation felt by the nerve cells are then transmitted to the brain by optic nerve. : 

5. EYE LENS- I t is a convex lens. It focuses the light on retina . It forms real and inverted image of object On retina. 6. RETINA - A screen on which an image is formed on the eye. It is behind the lens. It contains several nerve cells. It consists of light sensitive cells. 7. OPTIC NERVE - The retina contains several nerve cells. Sensation felt by the nerve cells are then transmitted to the brain by optic nerve.

TWO TYPES OF CELLS- 1. CONES- They are sensitive to bright light. Cones sense colour. 2. RODS- They are sensitive to dim light. BLIND SPOT- At the junction of optic nerve and retina, there are no sensory cells, so no vision is possible at that spot. This is called blind spot. : 

TWO TYPES OF CELLS- 1. CONES - T hey are sensitive to bright light. Cones sense colour. 2. RODS - T hey are sensitive to dim light . BLIND SPOT- At the junction of optic nerve and retina, there are no sensory cells, so no vision is possible at that spot. This is called blind spot.

WORKING OF EYE: 

WORKING OF EYE Light rays coming from object enters through pupil on eye lens which converts light rays and produce real and inverted image of object on retina . The image thus formed is conveyed to brain by optic nerve and give rise to sensation of vision.

NEAR POINT- The minimum or least distance at which the object can be seen clearly with out strain in the eye is called near point. Its value is 25 cm. FAR POINT- The farthest distance at which the object can be seen clearly is called far point. : 

NEAR POINT- The minimum or least distance at which the object can be seen clearly with out strain in the eye is called near point . I ts value is 25 cm. FAR POINT- The farthest distance at which the object can be seen clearly is called far point.

DEFECTS OF VISION OF EYE: 

DEFECTS OF VISION OF EYE 1. MYOPIA (NEAR SIGHTEDNESS) - A person can see nearby objects clearly but can not see the distant objects so clearly. The defect can be corrected by using spectacles fitted with concave lens. 2. HYPERMETROPIA (LONG / FAR SIGHTEDNESS)- A person can see distant objects clearly but can not see the nearby objects so clearly. The defect can be corrected by using the spectacles fitted with convex lens.

EYE DISEASE- CATARACT: 

EYE DISEASE- CATARACT In old age, eye sight becomes foggy. It is due to the eye lens becoming cloudy. There is a loss of vision. It is possible to treat the defect by removing opaque lens and inserting artificial lens.

CARE OF EYE: 

CARE OF EYE If there is a problem in eye, we should go to an eye specialist and have a regular check up. 2. It is advised , to use suitable spectacles. 3. Too little or too much light is bad for eyes, use suitable lights. 4. Do not look at the sun directly. 5. If dust particles enter in eye, wash your eyes with clean water. 6. Always read at normal distance for vision.