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Q19 (CDS-I/2004) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Human anatomy physiology Answer Verified

The normal eye is adapted for near and far vision. This is mainly due to

Result
Your answer: —  Â·  Correct: C
Explanation

The human eye's ability to focus on objects at varying distances, known as accommodation, is primarily facilitated by the ciliary muscles [c1][t3]. These muscles modify the curvature and focal length of the crystalline lens [c1]. When viewing distant objects, the ciliary muscles relax, causing the lens to become thin and increasing its focal length [c1][t6]. Conversely, for near vision, the ciliary muscles contract, which reduces tension on the zonular fibers and allows the lens to become thicker and more convex [c1][t1]. This increase in curvature decreases the focal length, enabling a sharp focus on nearby objects [c1][t4]. While the lens's convex nature is essential for refraction, the dynamic adjustment required for both near and far vision is specifically driven by the action of the ciliary muscles [c1][t2]. The iris merely regulates light entry by controlling pupil size [c2].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.1.1 Power of Accommodation > p. 162
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.1 THE HUMAN EYE > p. 161
  3. [3] https://www.sciencedirect.com/topics/neuroscience/ciliary-muscle
  4. [4] https://www.ncbi.nlm.nih.gov/books/NBK542189/
  5. [5] https://pmc.ncbi.nlm.nih.gov/articles/PMC9363677/
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