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• normal vision- 25 cm to infinity
• near point- 25 cm the closest distance at which an object can be clearly seen
• far point- 25cm farthest disatnce
• hyperopia- farsightedness, distant objects are clear but close objects appear blurry
• presbyopia- loss of accommodation due to aging
• myopia- nearsightedness, near objects are clear but far objects appear blurry. the far point is not at infinity
• astigmatism- unequal curvature of cornea or lens causing distorted images
• myopia can be corrected by the use of diverging lens
• hyperopia can be correct by using converging lens
• presbyopia corrected by

  bifocal near to far vision

  trifocal near, middle and far vision
• Progressive lenses change magnifying power from near to middle to far vision gradually