Question

Distance between the focusing parts of the two human eyes is about
A) 2cm
B) 4cm
C) 7cm
D) 10cm

Answer 1

Hint: Here we will discuss the focusing power of the human eye by comparing their accommodation power. It acts like a reflection and it can be controlled sometimes.

Complete Answer:
- Every vertebrate organism can focus objects by their accommodation power. Focusing means to clean the image of the object at each distance.
- The change in focal power i.e. reciprocal focal length is resulted into the reduction of the zonular tension by the induction of ciliary contraction of muscle. It occurs in between very few milliseconds i.e. 225-255 milliseconds.
- By increasing age, the accommodation amplitude is declined. When a person is 46-50 years old, the accommodation occurs in less than 2 dioptres and the person loses its ability of focusing on very close objects. And hence the person needs glasses or bifocal lenses for reading or working.
- Again in the age of about 70-75 years, about 1 dioptre accommodation power is decreased. It is better summarized in Duane’s Curves.
- At a young age i.e in about 5-6 years accommodation power remains very smooth. A human eye can focus the objects from near distance to extremely infinite distance.

Hence Option C: 7cm is the correct answer.

Note: The most far distance which can be focused by the human eye is called farpoint of the human eye and the normal distance that can be focused by the human eye is called nearpoint eye. The distance of the farpoint eye can be 25cm to infinite.