Basic ocular anatomy and diagnostics (Proceedings)


Basic ocular anatomy and diagnostics (Proceedings)

Apr 01, 2009

Basic Anatomy of the Eye

  • Orbit
  • Eyelids
  • Nasolacrimal System
  • Cornea/Sclera
  • Lens
  • Uvea
  • Aqueous/Vitreous
  • Iridocorneal Angle
  • Retina
  • Optic Nerve & Brain

The Orbit

  • Orbit= the "camera case" enclosing the eye
  • Made of bone, ligament, fat, muscle, salivary gland, roof of mouth
  • A mass behind the eye can push the eye out and/or protrude through soft tissue into the mouth*

The Eyelids

  • Eyelids= "lens cover" or "windshield wipers" of the eye
  • Act to protect and lubricate the surface of the eye

o Mechanical protection
o Meibomian glands of eyelids produce the oily component of the tears
o Spread tears (and foreign material) across surface & toward drainage system
  • Outer layer is thin skin
  • Muscles to close (orbicularis oculi) and open (levator palpebrae superioris) lids
  • Poorly developed supportive tarsal plate in dogs/cats
  • Meibomian glands in tarsus
  • Inner surface lined with conjunctiva
  • Cilia (eyelashes) arise from the lid margins*
  • Eyelids= skin, so can get all the skin diseases

o Bacterial
o Parasitic
o Allergic
o Auto-Immune
o Neoplastic
  • Eyelid glands can also become infected and/or inflamed, develop tumors

The Third Eyelid
  • Most domestic species have some variation of this structure
  • Acts to protect the eye when it is drawn over its surface passively*
  • T-shaped cartilage core coated by conjunctiva
  • Important tear-producing gland located behind and at its base
  • Von Graefe or other atraumatic forceps are used to look behind the third eyelid for foreign bodies, follicles

The Nasolacrimal System

  • Tear film coats cornea

o Meibomian glands produce thin fatty outer portion of tear film
o The lacrimal & third eyelid glands produce the thick middle watery tear layer
o Goblet cells within conjunctiva produce inner mucus layer
  • After tear production, tears are flushed by lids toward upper & lower punctae
  • Tears drain from lacrimal punctae→ canaliculi→ sac→ NL ducts→ nose/mouth
  • Obstruction at any point causes failure of drainage (tearing)*

Cornea & Sclera

  • Together make up the outer, fibrous coat of the eye
  • CORNEA= clear "windshield" and most important focusing structure of eye
  • SCLERA= the support mechanism
  • Cornea is a multilayered structure
  • Pumps in the innermost endothelium (esp) and outermost epithelium act to dehydrate it
  • The middle stroma is hydrophilic (water-loving)*
  • Corneal clarity achieved due to:

o Relative dehydration
o Lack of blood vessels
o Strict organization of collagen in stroma
  • The sclera is opaque because it lacks these qualities
  • Scarred cornea is also opaque to varying degrees b/c of fibrosis