Eyeball (Bulbus Oculi)
2. Middle vascular tunic (tunica vasculosa bulbi) or uvea
Figure 1: Internal structures of the eye.
Source: Ross M.H. and Pawlina W. (2006) Histology a text and atlas with correlated cell and molecular biology, 5th edn., USA: Lippincott Williams & Wilkins.
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The eyeball or bulbus oculi consists of three thin tunics:
1. Outermost fibrous tunic (tunica fibrosa bulbi)
Source: Ross M.H. and Pawlina W. (2006) Histology a text and atlas with correlated cell and molecular biology, 5th edn., USA: Lippincott Williams & Wilkins.
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The eyeball or bulbus oculi consists of three thin tunics:
1. Outermost fibrous tunic (tunica fibrosa bulbi)
- Sclera
- Posterior part of eye
- Covered by vagina bulbi
- Meets cornea at the limbus corneae
- Opaque à white of the eye
- Dense collagen and elastic fibres à shape of eye
- Provides surface area for attachment of extraocular muscles
- Ciliary arteries, scleral venous plexus, vorticose veins and nerves
- Cornea
- Anterior part of eye
- Meets sclera at limbus
- Bulges forward slightly
- Transparent à allow light to enter eye
- Dense connective tissue arranged in a lamellar form
- Constant removal of interstitial fluid
- Avascular
- Transmission and refraction of light
- Cells receive nutrients from limbic vessels, aqueous humour or lacrimal fluid
- Branches of ophthalmic nerve à corneal reflex closes eyelids when cornea is touched
2. Middle vascular tunic (tunica vasculosa bulbi) or uvea
- Choroid
- Extends from optic nerve to limbus
- Pigmented connective tissue and network of blood vessels
- Capillaries on internal surface
- Provides nutrition to retina
- Redness of fundus, located on inner surface of posterior part of eye
- Tapetum Lucidum (except humans and pigs)
- Dorsal part of fundus
- Colored, light reflecting area à shine to animal’s eyes when light is shone on it
- Avascular
Figure 2: Anterior section of the eye.
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!!!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!!!
- Ciliary body
- Thickened zone
- Ciliary processes
- Radial ridges that converge towards center of lens
- Suspends lens by zonular fibres
- Produce aqueous humor
- Ciliary muscles
- Between the ciliary body and sclera
- Regulate lens curvature for accommodation
- Iris
- Projection into eye cavity between cornea and lens
- Attached to sclera by pectinate ligament
- Number of pigmented cells and type of pigment à colour of eye
- Pupil
- Opening in the center à light enters eye
- Presence of retinal and choroidal pigmentation à Black
- Black walls absorb scattered and reflected light à prevent it from striking retina a second time, which would contribute to blurred vision
- Iris smooth muscle and sphincter
- Regulates size of pupil à regulate amount of light reaching retina
- Iris sphincter pupillae muscle contraction à constriction of pupil or miosis
- Radial dilator pupillae muscle contraction à dilation of pupil or mydriasis
- Anterior and posterior chambers
- Space between lens and cornea divided by the iris
- Communicate through pupil
- Contain aqueous humor
- Produced by epithelium of ciliary processes
- Maintenance of intraocular pressure
- Light refraction
- Nourishment of cornea and lens
- Retina
- Extends from optic nerve to papillary margin
- Nervous tissue with light-sensitive receptor cells
- Ora serrata divides retina into optical retina, pars optica retinae and non-optical retina, pars ceca retinae.
- Optic disc:
- Center of optic nerve
- Axons of ganglion cells
- Arterioles and venules
- Visual stimuli translated into nerve impulses and transmitted to the brain for visual interpretation via the optic nerve
Lens
- Solid but elastic
- Biconvex
- Regularly arranged fibers in a concentric pattern à transparent
- Zonular fibres of ciliary processes attaches to capsule perimeter of lens
- Refraction of light
Vitreous body
- Between the lens and retina
- Clear gel: vitreous humour and stroma of fibres
- Holds retina against choroid
- Protects retina by acting as a shock absorber
- Transparent medium for light to strike retina
References
- Dyce K.M., Sack W.O. and Wensing C.J.G. (2010) Textbook of veterinary anatomy, 4th edn., Missouri: Saunders Elsevier.
- Evans H.E. and Lahunta A. (2010) Guide to the dissection of the dog, 7th edn., Missouri: Saunders Elsevier.
- Ross M.H. and Pawlina W. (2006) Histology a text and atlas with correlated cell and molecular biology, 5th edn., USA: Lippincott Williams & Wilkins.
