Power of Accommodation

  

Power of Accommodation – The Eye’s Ability to Focus

The power of accommodation refers to the ability of the human eye to adjust its focal length so that objects at different distances can be seen clearly. This is achieved by changing the curvature of the eye lens with the help of ciliary muscles.

Subtopics of Power of Accommodation:

1. Structure and Function of the Eye Lens

  • The eye lens is a convex lens made of a flexible, transparent material that allows refraction of light onto the retina.

  • The ciliary muscles control the shape of the lens, helping it to focus on objects at varying distances.

2. Mechanism of Accommodation

  • When viewing a near object, the ciliary muscles contract, making the lens thicker, thus decreasing its focal length.

  • When viewing a distant object, the ciliary muscles relax, making the lens thinner, thereby increasing its focal length.

  • This adjustment ensures that the image is always formed on the retina, maintaining clear vision.

3. Limits of Accommodation

  • The minimum distance at which an object can be seen clearly without strain is called the near point (least distance of distinct vision), which is 25 cm for a normal human eye.

  • The far point of the eye is infinity, meaning distant objects are seen clearly without effort.

  • The range of accommodation lies between 25 cm and infinity.

4. Defects Related to Power of Accommodation

  • When the eye loses its ability to adjust focal length properly, it leads to vision defects such as:

    • Myopia (Nearsightedness): The eye can focus on nearby objects but not distant objects due to an elongated eyeball or excessive curvature of the lens.

    • Hypermetropia (Farsightedness): The eye can focus on distant objects but not nearby objects due to a shorter eyeball or less curved lens.

    • Presbyopia: Occurs with aging when the lens loses its flexibility, making it difficult to focus on near objects.

Class 10 CBSE Notes on Power of Accommodation

  • The power of accommodation is the ability of the eye to adjust its focal length to see objects at different distances.

  • The ciliary muscles play a key role in adjusting the shape of the eye lens.

  • The near point for a normal human eye is 25 cm, and the far point is infinity.

  • The eye lens becomes thicker for nearby objects and thinner for distant objects.

  • Defects in accommodation include myopia, hypermetropia, and presbyopia, which require corrective lenses for clear vision.

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