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Comprehensive Overview of Eye Anatomy

Nov 26, 2024

Anatomy of the Eyeball

Introduction

  • Understanding the anatomy of the eye is crucial before delving into phototransduction and optic pathways.
  • Focus areas include the tunics of the eye, segments, aqueous humor flow, lacrimal flow, and relevant clinical correlations.

Tunics of the Eye

  1. Fibrous Tunic

    • Composed of:
      • Sclera: Opaque connective tissue. Has three layers:
        • Episclera: Dense fibrous connective tissue.
        • Sclera Proper: Rich in collagen fibers, providing toughness.
        • Lamina Fusca: Pigmented layer.
      • Cornea: Transparent, five layers - epithelial (rich in nociceptors), Bowmanโ€™s membrane, stromal layer, Descemet's membrane, endothelial layer.
      • Function: Allows light passage, minimal blood supply, low risk of rejection in transplants.
  2. Vascular Tunic (Uvea)

    • Composed of:
      • Choroid: Pigmented, prevents light scattering, and has a rich vascular supply.
      • Iris: Controls pupil size; contains dilator (sympathetic) and sphincter (parasympathetic) pupillae muscles.
      • Ciliary Body: Ciliaris muscle (involved in accommodation), ciliary processes (produce aqueous humor).
  3. Sensory Tunic

    • Primarily the Retina, consists of:
      • Neural layer with photoreceptors (rods and cones), bipolar, ganglion cells, amacrine, and horizontal cells.
      • Pigmented layer absorbs light, prevents scattering.
      • In proximity to choroid for vascular supply.

Segments of the Eye

  • Anterior Segment: Contains anterior and posterior chambers, separated by the iris.
  • Posterior Segment: Posterior to the lens, filled with vitreous humor.

Aqueous Humor Flow

  • Produced by ciliary processes, flows from posterior to anterior chamber, drained via scleral venous sinus (canal of Schlemm).

Vitreous Humor

  • Fills the posterior segment, maintains retinal position, transmits light, contributes to intraocular pressure.

Clinical Correlations

  • Sclera: Jaundice can cause yellowing.
  • Cornea: Minimal immune presence allows transplant success.
  • Lens: Cataracts result from crystalline protein clumps, influenced by factors like diabetes and smoking.
  • Retina: Detachment can occur when vitreous humor leaks between neural and pigmented layers.

Lacrimal Flow

  • Lacrimal gland produces tears, flow across the eye and drain into the nasal cavity.

Other Eye Structures

  • Palpebra (Eyelids): Conjunctiva covers inner lid, tarsal plates provide structure and gland secretions.
  • Optic Nerve: Exits eye at the optic disc, passes through lamina cribrosa.

Conclusion

  • In the next session, focus will be zooming into the retinal layers and phototransduction process.