1. BY P.K.BERA. & N.MAKHIJA.

2. VIII TO X CLASSES AGE GROUP : 13 TO 15 YEARS.

3. LEARNING OBJECTIVES: 1.TO KNOW ABOUT INTERNAL STRUCTURE OF EYE. 2.TO KNOW THE DEFECTS OF VISION. 3.RECTIFYING THE DEFECTS OF VISION.

4. HUMAN EYE

6. Light rays entering the eye are refracted, or bent, when they pass through the lens. Normal vision requires that the rays focus on the retina.

7. If the eyeball is too long, an accurately focused image falls short of the retina. This is called myopia, or shortsightedness. A shortsighted person sees distant objects unclearly.

8. Longsighted focus, or hyperopia, results when the eyeball is too short. In this case, an accurately focused image would fall behind the retina. These conditions can also occur if the muscles of the eye are unable to alter the shape of the lens to focus light rays accurately.

9. NORMAL EYE WHEN WE LOOK NEARBY OBJECTS; CILIARY MUSCLES CONTRACT.LENS ASSUMES ROUND SHAPE. IMAGE FORMS AT RETINA FARAWAY OBJECTS; CILIARYMUSCLES REFLEXED.LENS ASSUMES THIN SHAPE. IMAGE FORMS AT RETINA.

10. MYOPIA OR NEAR SIGHTEDNESS PERSONS CANNOT SEE DISTANT OBJECTSCLEARLY. IMAGE FORMS INFRONT OF RETINA. A CONCAVE LENS BRINGS IMAGE BACK TO RETINA.

11. HYPERMETROPIA OR FAR SIGHTEDNESS PERSONS CAN NOT SEE NEARBY OBJECTS CLEARLY. IMAGE FORMS BEHIND THE RETINA. A CONVEX LENS BRINGS IMAGE BACK TO RETINA.

12. ACKNOWLEDGEMENT 1.ENCARTA ENCYCLOPEDIA 2000 2.NCERT BOOK OF CLASS VIII.