The closest distance of distinct focus for a healthy human eye is_______________?
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Answer: B. 25 cm
Explanation
The normal human eye cannot focus sharply on objects closer than a specific limit. Ciliary muscles reach their maximum tension limit when viewing objects at this close range. Conventionally, this standard near point distance is established internationally as twenty-five centimeters. The near point distance increases as people age due to natural eye lens stiffening. Optometrists test this focusing limit during routine comprehensive vision examinations. Young children often possess a closer near point due to high lens elasticity.
Reading books or viewing smartphones closer than twenty-five centimeters causes eye strain. Magnifying glasses help individuals with impaired vision view objects closer than twenty-five centimeters. Optical instruments are calibrated assuming a standard human eye near point of twenty-five centimeters. Fifteen centimeters is generally too close for a healthy adult human eye to focus. Thirty centimeters is slightly farther than the standard clinical reference near point value. Forty centimeters exceeds the standard near point for healthy young adult human eyes.
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