Prescription of presbyopic lens to a 50 year old emmetropic individual is
Ans. (c) +1.50Ref: Khurana optics 2/e, p. 101, Elkington optics 4/e, p. 237Rough estimate for presbyopic add45 years: +1.00 to +1.25 D50 years: +1.50 to +1.75 D55 years: +2.00 to +2.25 DIn order to focus on an object at a reading distance of 25 cm, the emmetropic eye must accommodate by 4 D. However, for comfortable near vision one-third of the available accommodation must be kept in reserve. Therefore, the patient will begin to experience difficulty or discomfort for near vision at 25 cm when his accommodation has decayed to 6 D. This usually occurs between 40 and 45 years of age. A person experiencing such difficulty and discomfort for near vision due to reduced amplitude of accommodation is said to be presbyopic.
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Elementary Optics