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Two persons, A and B are using lenses of power $+1.5\ \text{D}$ and $-1.5\ \text{D}$ respectively in their spectacles. Write the names of eye defects from which A and B are suffering. Write two causes for each defect of vision.
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• A is suffering from Hypermetropia ($\frac{1}{2}$ Mark)
• B is suffering from Myopia ($\frac{1}{2}$ Mark)
Causes of Hypermetropia (A)
(i) Focal length of eye lens is too long ($\frac{1}{2}$ Mark)
(ii) Eye ball has become too small ($\frac{1}{2}$ Mark)
Causes of Myopia (B)
(i) Excessive curvature of eye lens ($\frac{1}{2}$ Mark)
(ii) Elongation of eye ball ($\frac{1}{2}$ Mark) (3 Marks)
• B is suffering from Myopia ($\frac{1}{2}$ Mark)
Causes of Hypermetropia (A)
(i) Focal length of eye lens is too long ($\frac{1}{2}$ Mark)
(ii) Eye ball has become too small ($\frac{1}{2}$ Mark)
Causes of Myopia (B)
(i) Excessive curvature of eye lens ($\frac{1}{2}$ Mark)
(ii) Elongation of eye ball ($\frac{1}{2}$ Mark) (3 Marks)