Describe the process of accommodation in the human eye. Include in your answer: the roles of the ciliary muscle and suspensory ligaments, changes in the shape of the lens, and how these changes affect the focal length of the eye. Use diagrams or equations only if necessary; the explanation should be clear and detailed.
Answer
During accommodation, the ciliary muscle contracts, slackening the suspensory ligaments. This reduces the tension on the lens, allowing the lens to become more convex (thicker) and increasing its refractive power. The increased curvature shortens the focal length so that light from a near object is brought to a sharp image on the retina.
Step-by-step solution
- 1. Contraction of the ciliary muscle removes tension from the suspensory ligaments.
- 2. The lens, supported by these ligaments, bulges inward and becomes more spherical (increased curvature).
- 3. The increased curvature raises the lens’ refractive power, shortening the focal length of the eye.
- 4. As a result, the eye can focus on a near object without changing the cornea’s power.
- 5. When the ciliary muscle relaxes, ligaments tighten, the lens flattens, and the eye returns to its normal focal length for distant vision.
Common mistake: Neglecting the role of suspensory ligaments
Concept tested: Accommodation mechanism
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