Layers of the Eye

Overview

• The eye is composed of three tunics (or layers):
  1. Fibrous Tunic
  2. Vascular Tunic
  3. Sensory Tunic

1. Fibrous Tunic

• Sclera:
  • The white portion of the eye
  • Made of dense irregular tissue
  • Very tough
• Cornea:
  • The clear portion covering the iris
  • Located at the front of the eye
• Optic Nerve:
  • Sensory nerve (Cranial Nerve II)
  • Located at the back of the eye

2. Vascular Tunic

• Contains many blood vessels
• Composed of:
  • Choroid Coat:
    • Covers approximately three-fourths of the eye
    • Connected to the ciliary bodies
    • Edges meet the ciliary bodies at the Ora Serrata (scalloped edge)
  • Ciliary Bodies:
    • Made of smooth muscle
    • Surround the pupil
    • Connected to the lens by zonular fibers (suspensory ligaments)
    • Contract to change the lens' shape
  • Iris:
    • Colored portion of the eye
    • Made of smooth muscle and pigmented epithelial tissue
    • Contains the pupil (a hole for light entry)
• Lens:
  • Held in place by zonular fibers
  • Changes shape to focus light

3. Sensory Tunic

• Composed of the retina
• Retina:
  • Thin layer covering two-thirds to three-fourths of the eye
  • Contains photoreceptors: cones (detect color) and rods (detect black and white)
  • Macula Lutea:
    • Central area with most rods and cones
    • Provides acute vision
  • Fovea Centralis (Central Fovea):
    • Located in the center of the macula lutea
    • Contains only cones (color detection)
  • Optic Disc:
    • Point where retina exits the eye and becomes the optic nerve
    • Known as the "blind spot"

Eye Chambers

• Vitreous Chamber:
  • Large chamber filled with vitreous humor (clear, jelly-like substance)
  • Helps maintain eye shape
  • Contains as much vitreous humor as you have from birth
• Anterior Cavity:
  • Composed of two chambers:
    • Anterior Chamber:
      • Between the back of the cornea and the front of the iris
    • Posterior Chamber:
      • Between the back of the iris and the front of the lens
      • Hard to see in models
  • Usually focus on anterior and vitreous chambers for examination