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
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 & SCLERA
- 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)*
- CORNEA & SCLERA
- 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
