Lecture Notes: Accommodation and Changes in Lens Structure

Overview

• Light path through the eye:
  • Cornea
  • Anterior cavity
  • Pupil
  • Lens
  • Posterior cavity
  • Retina
• Light Refraction: Light bends as it passes through substances of varying densities.

Main Focus: Accommodation

• Accommodation: The eye's ability to change focus from distant to near objects and vice versa.
• Achieved by changes in the shape of the lens.

Details of Accommodation

• Lens Structure:
  • Bends light to focus it on the fovea centralis, part of the retina with high cone concentration for clear images.

Lens Adjustment for Close Objects

• Close Object Focus:
  • Lens becomes rounder and thicker.
  • Focal Length: Distance between lens and retina decreases.
  • Increased Refractive Power: Light bends more sharply.
  • Ciliary Muscles: Contract, loosens ciliary processes, making the lens more rounded.

Lens Adjustment for Distant Objects

• Distant Object Focus:
  • Lens becomes flatter and thinner.
  • Focal Length: Increases as lens stretches.
  • Decreased Refractive Power: Light bends less sharply.
  • Ciliary Muscles: Relax, pulling processes tight, stretching the lens.

Age-related Changes

• Decreased Accommodation with Age:
  • Reduced flexibility of the lens.
  • Weaker ciliary muscles.
  • Difficulty focusing on objects increases with age.

Recap

• Accommodation Process:
  • Lens shape change allows focus adjustment from near to far and vice versa.
  • Supported by ciliary muscles and processes.
  • Close view: lens is rounder, increased refraction, decreased focal length.
  • Distant view: lens is flatter, decreased refraction, increased focal length.