Lecture Notes: The Process of Accommodation

Introduction

• Accommodation is a reflex changing the refractive power of the lens.
• Allows vision of both near and distant objects.
• Glasses can assist when this process malfunctions.

Structure of the Eye

• Cornea and Lens:
  • Both refract or bend light.
• Ciliary Muscles and Suspensory Ligaments:
  • Control the shape of the lens.

Focus on the Retina

• Fovea:
  • Spot on the retina where light must be focused.
• Light Refraction:
  • Cornea primarily refracts light.
  • Lens fine-tunes refraction to converge light on the fovea.

Near and Distant Objects

• Close Objects:
  • Require more refraction.
  • Lens becomes short and fat to refract more.
• Distant Objects:
  • Require less refraction.
  • Lens stretches out to reduce refractive power.

Mechanism of Accommodation

• Ciliary Muscle and Suspensory Ligaments:
  • Ciliary muscle contracts for near objects, loosening ligaments, allowing lens to fatten.
  • Ciliary muscle relaxes for distant objects, tightening ligaments, stretching the lens.

Key Points

• Ciliary muscle moves inwards towards the lens when contracted.
• Suspensory ligaments can only be pulled taut or slacken, not contract.

Vision Deficiencies

• Long-Sightedness (Hyperopia):
  • Lens can't refract enough for near objects.
  • Corrected with convex lenses in glasses.
• Short-Sightedness (Myopia):
  • Lens over-refracts light for distant objects.
  • Corrected with concave lenses in glasses.

Conclusion

• Long-sightedness (hyperopia) and short-sightedness (myopia) have specific corrective measures through lens adjustments in glasses.