Anatomy - Blood supply to the eye

Blood supply
Vascular tunic blood supply

Figure 1: Arterial supply of vascular tunic
Source: Evans H.E. and Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.

Figure 2: Venous drainage of vascular tunic
Source: Evans H.E. and Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.
  • Choroid is a pigmented vascular layer
  • Plexus of arteries, arterioles, veins & venules
  • Supported by collagenous, elastic stroma
  • Subdivded into:
    • Outer large-sized layer
      • Terminal branches of ciliary arteries & vorticose veins
    • Inner middle-sized layer
      • Branches of choroidal veins that fan outward from point where vorticose veins penetrate sclera
      • Empties choroidal capillary layer
      • Nourishes outer layer of retina


Arterial system of the eye
Figure 3: Lateral aspect of the arteries supplying the orbit
Source: Evans H.E. and Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.

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Figure 4: Dorsal aspect of the orbital arteries and the base of the cranium.
Source: Evans H.E. and Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.
  • The major blood supply to the eye is from the external carotid artery
  • Venous blood leaves from the angular vein, deep facial vein & ophthalmic veins
  • Superficial temporal artery
    • Supplies branches to adjacent structures
    • Superior & inferior lateral palpebral arteries
    • Lateral aspect of eyelids & conjunctiva
  • Malar artery
    • Superior & inferior medial palpebral branches
    • Supplies branches that go to third eyelid, ventral oblique muscle, nasolacrimal duct
  • Maxillary artery
    • Gives rise to external ophthalmic artery
  • External ethmoidal artery
    • Arise from external ophthalmic artery
    • Supply ventral, medial & lateral rectus muscle
    • Supply ventral vasciculi of retractor bulbi
    • Supply superficial gland of third eyelid
  • Cillary vessels pierce into sclera posteriorly
    • Forms a complete circle in through the sclera
    • Supplies capillaries of limbal region
    • Supplies ciliary body & iris
  • Muscular branch
    • Supplies branches to lateral, dorsal rectus muscles
    • Dorsal fascicles of retractor bulbi
    • Dorsal oblique muscle
    • Levator palpebral superioris muscle
  • Lacrimal artery
    • Supplies lacrimal gland
  • Internal ophthalmic artery
    • Passes through optic canal on dorsal surface of optic nerve
    • Runs rostrally on optic nerve 
    • Anastomose with external ophthalmic artery
  • Long posterior ciliary arteries
    • Supply anterior segment of eye
  • Short ciliary arteries
    • Forms ring of 6 to 10 pillars around optic nerve in lamina crisbosa region
    • Gives rise to retinal arteries


 Figure 5: Arterial vessels of the eye. 1: Maxillary a., 3: External ophthalmic a., 4: Anastomosis between external and internal ophthalmic aa., 5: Lacrimal a., 6: Short posterior ciliary aa., 7: Retinal aa., 8: Long Posterior ciliary aa., 9: Anterior ciliary aa., 10: Greater arterial circle of iris, 11: Muscular branches, 12: Supraorbital a., 13: External ethmoidal a., 14: Malar a., 15: Palpebral branches, 16: Vorticose veins, 17: Optic nerve.
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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Venous system of the eye

  • There are three routes in which blood can drain from the orbit:
    1. Angular vein to facial vein
    2. Ophthalmic plexus to cavernous sinus & maxillary vein
    3. Anatomosis of ventral external ophthalmic vein to deep facial vein
  • These three routes are interconnected  & filled with orbital venography


Figure 6: Venous drainage of the eye and orbit of the dog. 
Source: Maggs D.J., Miller P.E. and Ofri R. (2013) Slatter's fundamentals of veterinary ophthalmology, 5th edn., Missouri: Elsevier.

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Figure 7: Veins of the eye
Source: Evans H.E. and Lahunta A. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.

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  • Angular vein
    • Continues to facial vein dorsally & caudally
    • Lacks valves à blood flow through either from orbit to facial vein or facial vein to ophthalmic vessels
  • Dorsal external ophthalmic vein
    • Largest intraorbital vein
    • Posterior aspect of eye à large anastomotic branch to dorsal oblique muscle & join ventral external ophthalmic vein
  • Lacrimal vein
    • Drains lacrimal gland
  • Dorsal external ophthalmic vein & ophthalmic plexus joins ventral external ophthalmic vein
    • Blood here leaves orbit as emissionary vein of orbital fissure
  • Ventral external ophthalmic vein 
    • Receives numerous muscular branches
    • Receives large anastomosis branch from dorsal ophthalmic 
    • Drainage from ventral pair of vorticose veins
  • Eyeball drains into ophthalmic vessels through retinal, ciliary, vorticose veins
    • Ciliary veins pair with ciliary arteries as satellite veins
    • Retinal veins join posterior ciliary veins
    • No central retina vein in dog
  • Major drainage of vascular tunic as mentioned above is via vorticose veins
    • Vorticose veins
      • Four in number
      • Penetrate sclera near equator between insertions of four rectus muscles


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. (2012) Miller's anatomy of the dog, 4th edn., Missouri: Saunders Elsevier.
  3. Gelatt K.N. (2007) Veterinary opthalmology, 4th edn., Oxford: Blackwell Publishing.
  4. Maggs D.J., Miller P.E. and Ofri R. (2013) Slatter's fundamentals of veterinary ophthalmology, 5th edn., Missouri: Elsevier.
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