Anatomy - Ocular Adnexa

Ocular Adnexa 

Orbit  


Figure 1: Lateral view of skull.
Source: Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.

  • Cavity housing eyeball and its adnexa among orbital fat
  • Frontal, lacrimal, maxillary, presphenoid, palatine and zygomatic bones of skull
  • Periorbita 
    • Fibrous sheath of connective tissue and smooth muscle
    • Surrounds eyeball, its muscles, vessels and nerves

Orbital fascia

Figure 2: Schematic transection of orbital fasciae and orbital structures at the level of the eyeball.
Source: Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.

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Superficial muscular fascia 
  • Lies within priorbita 
  • Abundant adipose tissue
  • Envelops levator palpebrae superioris and lacrimal gland

Deep muscular fascia 
  • Fibrous sleeve 
  • Extends from eyelids and limbus 
  • Surrounds eyeball, ocular muscles and optic nerve
  • Vagina Bulbi 
    • Surrounds eyeball
    • Narrow episcleral space between eyeball and vagina bulbi à movement of  eyeball against retrobulbar fat

Eyelids (Palpebrae)

Figure 3: Sectioned eyelid viewed obliquely from behind.
Source: Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.

Click HERE to test yourself!!!
  • Arise from bony margins of orbit 
  • Moisten cornea by distributing tears or lacrimal fluid
  • Blinking for protection against trauma
  • Eyelashes (cilia) 
    • Protects eye from particles
    • Small ciliary and sebaceous glands
  • Levator palprbrae superioris elevates upper eyelid
  • Orbicularis oculi closes eye
  • 3 smooth muscle sheets 
    • Maintain normal eye protrusion and retracted eyelid position
  • Tarsus
    • Thickened fibrous edge formed by orbital septum of periorbita
    • Tarsal ‘Meibomian’ glands 
      • Secrete lipid
  • Palpebral conjunctiva
    • Mucous membrane with goblet cells
    • Continues as bulbar conjunctiva on sclera and anterior epithelium on cornea
    • Conjunctival sac & fornix
      • Space between lids and eyeball
      • Fun fact: This is a hiding place for grass seeds
    • Highly vascular

Third Eyelid

Figure 4: The eye and ocular adnexal structures.
Source: McCracken T.O., Kainer R.A. and Carlson D. (2008) Color atlas of small animal anatomy: the essentials, 1st edn., Iowa: Lippincott Williams & Wilkins.
  • Nictitating membrane
  • Conjunctiva fold
  • Dorsoventral orientation between lacrimal caruncle and eyeball
  • Supported by a T-bar of cartilage
  • Kept retracted by smooth muscle (m. orbitalis) and sympathetic nervous system 
  • Gland of third eyelid
  • Eye protection and tear distribution
    • Tears enter eye on bulbar surface

References
  1. Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
  2. Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
  3. McCracken T.O., Kainer R.A. and Carlson D. (2008) Color atlas of small animal anatomy: the essentials, 1st edn., Iowa: Lippincott Williams & Wilkins.