Special Senses Module: Anatomy of the Eye

Overview

• Special senses have dedicated organs: vision, hearing, balance, smell, taste.
• Previous modules covered the tongue and nose.
• Focus of this module: anatomy of the eye and ear.

Learning Objectives

• Identify structures associated with the eye adnexa.
• Identify parts of the eye tunics.
• Identify boundaries of the eye chambers.
• Identify parts of the outer, middle, inner ear.

Anatomy of the Eye

Eye Components

• Eyeball and Accessory Structures contained within the orbit.
• Surrounded by periorbital fascia and fat.

Eye Adnexa

• Adnexa: Attachments or appendages that protect/support organ functions.
• Components:
  • Eyelid and Conjunctiva: Protection.
  • Lacrimal Apparatus: Moisture and nourishment.
• Eyelids (Palpebrae):
  • Thin skin layer; upper and lower lids.
  • Dogs have a third eyelid (nictitating membrane).
  • Tarsus: Fibrous plate supporting eyelid, contains tarsal glands.
• Conjunctiva:
  • Mucous membrane lining eyelid/eyeball.
  • Types: Palpebral (inner eyelid) and Bulbar (over eyeball).
  • Canthus: Meeting point of eyelids (medial and lateral).
• Lacrimal Apparatus:
  • Lacrimal glands: Secret tears.
  • Lacrimal sac/ducts: Convey tears to nasal cavity.
  • Lacrimal Caruncle: Triangular prominence at medial canthus.
  • Lacrimal Puncta: Openings into lacrimal canals near medial canthus.

Eye Tunics

• Three Layers:
  • Outer Fibrous Layer:
    • Sclera: White, protective outer coat.
    • Cornea: Transparent part allowing light entry.
  • Middle Vascular Layer:
    • Choroid: Vascular membrane inside sclera.
    • Ciliary Body: Contains muscles for lens accommodation.
    • Iris: Colored part, regulates pupil size.
  • Inner Nervous Layer (Retina):
    • Composed of photoreceptors, bipolar neurons, ganglion neurons.
    • Photoreceptors: Rods (dim light/shape) and Cones (color/sharpness).
    • Optic Disc: Blind spot, no photoreceptors.

Lens

• Transparent, biconvex body behind the iris.
• Function: Focus light on retina by changing shape (accommodation).

Eye Chambers

• Anterior Chamber: Between iris and cornea.
• Posterior Chamber: Between iris, ciliary body, lens.
• Vitreous Chamber: Behind lens, surrounded by retina.
• Fluids:
  • Aqueous Humor: Fills anterior/posterior chambers.
  • Vitreous Humor: Fills vitreous chamber.

Conclusion

• Covered eye adnexa, eye tunics, and eye chambers.
• Next module section: Anatomy of the ear.