Lecture Notes: Accommodation and Vision Correction

Key Concepts

• Accommodation: A reflex that adjusts the lens' refractive power for viewing near and far objects.
• Vision Correction: Use of glasses when accommodation is insufficient.

Anatomy of the Eye

• Cornea: Refracts light consistently.
• Lens: Fine-tunes refraction to focus light on the fovea.
• Ciliary Muscles: Control lens shape by contracting and relaxing.
• Suspensory Ligaments: Connect lens to ciliary muscles, change tension to adjust lens shape.

Process of Accommodation

Near Objects

• Light needs strong refraction.
• Lens becomes short and fat to increase curvature and refractive power.
• Mechanism:
  • Ciliary muscle contracts inwards.
  • Suspensory ligaments slacken.
  • Lens adopts a fatter shape.

Distant Objects

• Light requires less refraction.
• Lens stretches to decrease curvature.
• Mechanism:
  • Ciliary muscle relaxes.
  • Suspensory ligaments tighten.
  • Lens stretches out.

Vision Deficiencies

Long-sightedness (Hyperopia)

• Cause: Lens doesn't refract enough.
• Effect: Light focuses behind the retina, causing blurriness for nearby objects.
• Correction: Convex lenses in glasses add refracting power.

Short-sightedness (Myopia)

• Cause: Lens refracts too much.
• Effect: Light focuses before reaching the retina, causing blurriness for distant objects.
• Correction: Concave lenses in glasses spread light outwards to reduce over-refraction.

Summary

• Ciliary Muscle Action: Moves inwards for near objects (contracts) and relaxes for distant objects.
• Suspensory Ligaments: Adjust tension to modify lens shape but do not contract or relax themselves.
• Medical Terms:
  • Long-sightedness = Hyperopia
  • Short-sightedness = Myopia