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Least Distance of Distinct

What is Least Distance of Distinct Vision?

The least distance of distinct vision is defined as:
The minimum distance from the eye at which an object can be seen clearly and distinctly without strain.
It is also known as the near point of the human eye.

Value of Least Distance of Distinct Vision

For a normal human eye: $[ \boxed{D = 25\ \text{cm}} ]$ This value is used as a standard constant in numerical problems.

Why is Least Distance of Distinct Vision Important?

  • Determines maximum magnifying power
  • Used in simple microscope
  • Helps understand defects of vision
  • Indicates focusing ability of eye lens

Variation of Least Distance of Distinct Vision with Age

Age Group Least Distance
Children Less than 25 cm
Normal adult 25 cm
Old age More than 25 cm
In old age, the near point shifts away due to weakening of ciliary muscles (presbyopia).

Formula Using Least Distance of Distinct Vision

Maximum magnifying power of simple microscope: $[ M = 1 + \dfrac{D}{f} ]$ Where:
  • (D = 25) cm
  • (f) = focal length of lens

MCQs on Least Distance of Distinct Vision

MCQ 1

The least distance of distinct vision for a normal human eye is: A. 10 cm B. 15 cm C. 25 cm D. 50 cm ✅ Answer: C Explanation: Standard near point of a normal eye is 25 cm.

MCQ 2

Least distance of distinct vision is also known as: A. Far point B. Near point C. Retina point D. Optical centre ✅ Answer: B

Numerical Problems on LDDV

Numerical 1

The focal length of a simple microscope is 5 cm. Find its maximum magnifying power. Solution: $[ M = 1 + \dfrac{25}{5} = 6 ]$ ✅ Answer: 6
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