Anatomy of the Eyeball

Introduction

• Presented by Peter from Anatomy Zone
• Collaboration with TeachMeAnatomy
• Eyeball: bilateral and spherical organ responsible for vision
• Located in the bony cavity known as the Bony orbit

Anatomical Layers of the Eyeball

• The eyeball consists of three layers:
  • Fibrous Layer
  • Vascular Layer
  • Inner Layer

1. Fibrous Layer

• Outermost layer
• Comprises the Sclera and Cornea
  • Sclera:
    • Majority of the fibrous layer (~85%)
    • Provides shape and support to the eye
    • Attachment for extraocular muscles (responsible for eye movement)
    • Visible as the white part of the eye posteriorly
  • Cornea:
    • Transparent, located centrally at front of the eye
    • Refracts light entering the eye
    • Continuous with the sclera anteriorly

2. Vascular Layer

• Lies beneath the fibrous layer
• Comprises three parts:
  • Choroid:
    • Layer of connective tissue and blood vessels
    • Nourishes outer layers of the retina
  • Ciliary Body:
    • Encircles the eyeball
    • Comprises ciliary muscle and ciliary processes
    • Controls shape of lens through zonular fibers (suspensory ligament of the lens)
    • Contraction reduces size of ciliary body, allowing lens to round for near vision (accommodation)
  • Iris:
    • Circular structure with a central aperture (pupil)
    • Determines eye color
    • Contains circular fibers (sphincter pupilli muscle) and radial fibers (dilator pupilli muscle)
    • Controls pupil size:
      • Circular fibers constrict pupil (parasympathetic)
      • Radial fibers dilate pupil (sympathetic)

3. Inner Layer

• Consists of the Retina
• Composed of two cellular layers:
  • Neural Layer:
    • Contains photoreceptors (light-detecting cells)
    • Located posteriorly and laterally
  • Pigmented Layer:
    • Supports neural layer, continuous around eye
    • Anteriorly known as nonvisual retina
• Macula Lutea:
  • Yellowish area with high concentration of cones (for color vision)
  • Contains Fovea Centralis for high acuity vision
• Optic Disc:
  • Entry point of optic nerve, contains no light-detecting cells (blind spot)

Fluid Chambers in the Eye

• Anterior Chamber: Between cornea and iris
• Posterior Chamber: Behind iris and anterior to lens
• Chambers filled with Aqueous Humor:
  • Nourishes and protects the eye
  • Flows from posterior to anterior chamber via pupil
  • Drains into the canal of Schlemm
  • Obstruction can lead to glaucoma (increased intraocular pressure)
• Vitreous Chamber:
  • Fills eyeball with vitreous humor (gel-like substance)

Conclusion

• Overview of gross anatomy of the eyeball
• Next tutorial: Vascular Supply of the eye
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