Structure and Function of the Eye - Vision

Introduction

• The human eye is an organ that reacts to light, contributing to light perception, color vision, and depth perception.

Anatomy of the Eye

• Retina: Inner surface of the back of the eye; location of photoreceptive cells.
• Cornea: Transparent front layer; refracts light.
• Lens: Behind cornea; transparent convex structure; focuses light on retina.
• Iris: Colored part of the eye; regulates light entry.
  • Contracts in bright light, reducing pupil size.
  • Relaxes in dim light, enlarging the pupil.

Function of the Lens

• Focuses light on the retina and fovea centralis.
• Dynamic focusing ability:
  • Muscles change lens shape for near/far distances.
  • Loses flexibility with age, leading to presbyopia (farsightedness).

Vision Conditions

• Presbyopia: Image focuses behind the retina.
• Hyperopia: Similar to presbyopia; caused by a short eyeball.
• Myopia: Elongated eyeball; image focus falls in front of the retina.

Photoreceptors

• Two types: Rods and Cones.
• Rods:
  • Located at retina's outer edges.
  • Highly photosensitive.
  • Detect dim light; used for peripheral and nighttime vision.
• Cones:
  • Located near retina's center.
  • Respond to bright light; responsible for daytime color vision.

Fovea

• Located at eye center back; responsible for acute vision.
• High density of cones.
• In bright light, images are focused on the fovea.
• Peripheral vision uses rods for dim light objects.

Visual Pathways

• Cones outnumber rods in the fovea, enhancing color acuity.

Key Terms

• Cornea: Transparent front layer of the eye.
• Lens: Biconvex structure helping in light refraction.
• Iris: Colored part of the eye; controls light entry.
• Presbyopia: Age-related farsightedness due to lens elasticity loss.
• Hyperopia: Farsightedness caused by short eyeball.
• Myopia: Nearsightedness due to elongated eyeball.
• Retina: Converts light into neural signals.
• Rod: Light-sensitive cell at retina's edge.
• Cone: Color vision cell at retina's center.

Summary

• The eye functions through the interaction of its various parts to process light and focus images on the retina.
• Conditions like myopia and presbyopia affect vision due to structural differences in the eye.