? Photographs included in the presentation are courtesy of
Dr.Jonathan.J.Dutton and Dr.Thomas.G.Waldrop
(Atlas of Clinical and Surgical Orbital Anatomy)
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Learning Objectives
At the end of this class students shall be able to
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? Identify various structures of the eye? Have a basic understanding of the structure and functions of various
parts of the eye
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? OrbitLodges the eyeball
? Eye lids ?
? Cover and protect
? Lacrimal system-
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Secretes and drain tears? Extraocular muscles-
for ocular movements
? Layers of eyeball-
perform various functions
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Bony Orbit
? Made by 7
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Bones:-
? Frontal
? Zygomatic
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? Maxillary? Ethmoidal
? Sphenoid
? Lacrimal
? Palatine
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Frontal view of bony orbit
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Outer eye: Eyelids
The eyelids fulfill two main
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functions:? protection of the eyeball
? secretion, distribution and
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drainage of tears
The eyelid muscles
Lid structure and movement
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The levator muscle extends from
an attachment at the orbital apex
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to attachments at the tarsalplate and skin.
The lids are securely attached at
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either end to the bony orbital
margin by medial and lateral
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palpebral ligaments.Innervation
- Sensory innervation is from the trigeminal (fifth) cranial nerve, via
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the ophthalmic division (upper lid) and maxillary division (lower lid).- The orbicularis oculi is innervated by the facial (seventh) nerve.
- The levator muscle in the upper lid is supplied by the oculomotor
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(third) nerve.Blood supply
Network of blood vessels which form an anastomosis
between branches derived from the external carotid artery
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via the face and from the internal carotid artery via the orbit.Lymphatics
? Lymphatic fluid drains into the preauricular and submandibular nodes.
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? Preauricular lymphadenopathy is a useful sign of infective eyelid
swelling (especially viral).
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Lacrimal system
? Lacrimal gland
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? Lacrimal passage? Lacrimal puncta
? Lacrimal canaliculi
? Lacrimal sac
? Naso-lacrimal duct
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Tear production
? The lacrimal gland secretes
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most of the aqueouscomponent of the tear film
? Location: superotemporal
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part of the anterior orbit
? Innervation :
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parasympathetic fibrescarried by the facial nerve.
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Lacrimal Apparatus/Drainage systemExtraocular muscles
? 4 Recti
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? 2 ObliquesMedial rectus (MR)
Inferior Rectus (IR)
Superior rectus (SR)
Inferior oblique (IO)
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Superior Oblique(SO)Lateral Rectus (LR)
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Extra-ocular muscles
? Action results in eye movements
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? Medial Rectus --- Adduction? Inferior Rectus ---
Depression,Extorsion,Adduction
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? Superior Rectus ---
Elevation , Intorsion, Adduction
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? Inferior Oblique---Extorsion, Elevation, Abduction
? Superior Oblique---
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Intorsion, Depression,Abduction
? Lateral Rectus --- Abduction
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EXTRAOCULAR MUSCLESNerve supply of Extra Ocular Muscles
? Three Cranial Nerves supply the Extra Ocular Muscles
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? CN 3rd-Oculomotor-MR, IR, SR, IO? CN 4th-Trochlear--SO
? CN 6th- Abducens--- LR
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Overview of ocular anatomy
Conjunctiva
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? The conjunctiva is a mucous
membrane lining the eyelids.
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Covers the anterior eyeballup to the edge of the cornea.
? At the upper and lower
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reflections between eyeball
and eyelid, conjunctiva forms
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two sacs, the superior andinferior fornices .
Cornea and sclera
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The cornea and sclera form a
spherical shell which makes up
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outer wall of eyeball.
Cornea and sclera
? The sclera is :
- principally collagenous,
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- avascular (apart from some vessels on its surface)- relatively acellular.
It is perforated posteriorly by the optic nerve, and by sensory and
motor nerves and blood vessels to the eyeball.
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The cornea and sclera merge at the corneal edge (the limbus).Limbus
? Juncture between the cornea and the sclera
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? Nourishes peripheral cornea
? Assists in corneal wound healing
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? Pathway for aqueous outflow (contains trabecular meshwork andcanal of schlemm)
Corneoscleral limbus
? Transition zone:
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? anteriorbowman`s terminal-Descemet's terminal? posteriorscleral spuriris root
? 1.52.0mm width
? Appearance
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? Semitransparant zone
? White sclera
? Angle of AC
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The chief functions of the cornea
? Protection against invasion of microorganisms into the eye
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? Transmission and focusing (refraction) of light.Cornea
? Made up of 5 layers
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? Specialized Transparent Tissue? No blood vessels
? Primarily responsible for refracting light (43-44 diopters)
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? More nerve endings than anywhere else in the body
? Protection to the eye
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? The only part of the eye that is transplanted from one person to
another
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Cornea? Epithelium
? Bowman membrane
? Stroma
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? Descemetmembrane
(posterior limiting
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layer of cornea)
? Endothelium
Cornea- 5 layered
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Cornea
? Oval
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? transverse11.512mm? vertical10.511mm
? curvatureanterior 7.8mm
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posterior6.8mm? thicknesscentre0.50.55mm
periphery:1mm
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? Refractive index1.377
Cornea
1.Epithelium
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2.Bowman's membrane :
? 50m
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? 12? 5
m
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6 layers
? Squamous cell
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? No cell? Basal cell
? Collagen matrix
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? Renewing cycle7 days
? Scar
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Cornea3.Stroma
4. Descemet's membrane
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? 500 m
? 1012 m
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? 23 corneal cells? No structure
? 1matrixGAGs)
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? elasticity
? Fibrous lamina
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? 200? Secreted by endothelial cells
250 layers
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? Parallel to surface
? Basal membrane of
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endothelial cell? Parallel collagen fibers
? Ordered arrangement
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? Regeneration? Scar
Cornea
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5.Endothelium? 5 m
? Monolayer hexagon
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? 500 000 cells? Tight junctions
? Pump
UVEA
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? The uvea comprises the
? iris and ciliary body anteriorly
? choroid posteriorly
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Iris
? Consists of connective tissue
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containing muscle fibres, bloodvessels and pigment cells.
Its posterior surface is lined by a
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layer of pigment cells.
At its centre is an aperture, the pupil.
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The main function of pupil:Control light entry to the retina and
to reduce intraocular light scatter.
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Ciliary body
? The ciliary body is a specialised structure uniting the iris with the
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choroid.? Secretes aqueous humour
? Anchors the lens via the zonules, through which it modulates lens
convexity.
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? The posterior part of the ciliary body merges into the retina at the oraserrata.
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Choroid? The choroid, consisting of blood vessels, connective tissue and
pigment cells, is sandwiched between the retina and the sclera.
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? It provides oxygen and nutrition to the outer retinal layers.
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Lens? The discus-like lens comprises
a mass of long cells known as
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fibres. Has a hard nucleus
surrounded by less dense
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fibres, the cortex.? Relatively dehydrated
? Transparent.
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Aqueous humour
? Fills the anterior and posterior chambers.
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? The anterior chamber is the space between the cornea and the iris.
? Behind the iris and in front of the lens is the posterior chamber.
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They are connected by the pupil.Formation
? The ciliary body forms
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aqueous humour
? By ultrafiltration and
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active secretion.Drainage
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Aqueous circulates from theposterior to the anterior chamber
through the pupil.
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Passes through the trabecular
meshwork (a specialised tissue in
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the anterior chamber anglebetween the iris and the cornea).
From here aqueous drains into
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Schlemm's canal.Vitreous
? A thick, transparent gel like substance that fills the center of
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eyeball, giving it form and shape
? The vitreous body is 99% water but, vitally, also contains collagen
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fibrils and hyaluronan, which impart cohesion and a gel-likeconsistency.
? The vitreous is adherent to the retina at certain points,
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particularly at the optic disc and at the ora serrata.
?
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Volume - 4.5ml?
RI:1.3360aqueous humor
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Retina
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? Innermost layer of the eye.
? Converts light energyelectrical energy --->brain via the optic nerve
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? Composed of 10 layers.? Contains Photoreceptors
? Cones-near Center (seeing detail and color)
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? Rods- in Periphery (seeing in low light and movement)
Retina
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?Transparent ,thin
?
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Anterior rimora serrata
?
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3 parts:-?
Peripheral Retina
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?
Maculafovea
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?Optic disc
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Retina? Optic disc
? Only optic nerve fibers
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? Physiological blind spot? Macula
? Thinnest
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? Point of sharpest vision isin the fovea located in
the center of the macula
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Histology of retina
1 RPE
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2 Layers of Rods & Cones3 External Limiting Membrane
4 Outer Nuclear layer
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5 Outer Plexiform layer
6 Inner Nuclear layer
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7 Inner Plexiform Layer8 Ganglion Cell layer
9 Nerve Fibre layer
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10 Internal limiting membrane
Retina
? The blood supply of the retina is derived from the central retinal
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artery and vein, and from the choroid.? The retinal vessels enter and leave the eye through the optic nerve
and run in the nerve fibre layer.
A major arterial and venous branch, forming an 'arcade', supplies
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each of the retinal quadrants .Optic nerve
? The ganglion cell axons in the retinal nerve fibre layer make a right-
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angled turn into the optic nerve at the optic disc, which has nophotoreceptors and corresponds to the physiological blind spot.
? Behind the eyeball these axons become myelinated.
? Here the optic nerve is surrounded by cerebrospinal fluid in an
anterior extension of the subarachnoid space and is protected by the
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same membranous layers as the brain.Optic Nerve Pathways/Visual Cortex
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? Message is carried down the opticnerve through pathways to
occipital cortex; here vision
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becomes sight
? At the optic chiasm, the nasal
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nerve fibers cross; temporal nervefibers go straight back to cortex;
this arrangement impacts on
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visual fields
? Results in visual field losses can be
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predicted based on wheredamage is located on the optic
nerve
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Conclusion
? The human eye is lodged inside bony orbit and protected by
eyelids.
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? It has an outer protective scleral coat modified anteriorly to
form cornea
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? The middle layer or uvea consists of the ciliary body and irisanteriorly and choroid posteriorly
? The innermost layer is retina containing photoreceptors
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which lines the posterior two-thirds of choroid.
? The optic nerve carries visual information to the visual cortex.
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