Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Ophthalmology PPT 37 Ocular Anatomy Lecture Notes
Ocular Anatomy
Department of Ophthalmology
Acknowledgement
? Photographs included in the presentation are courtesy of
Dr.Jonathan.J.Dutton and Dr.Thomas.G.Waldrop
(Atlas of Clinical and Surgical Orbital Anatomy)
Learning Objectives
At the end of this class students shall be able to
? Identify various structures of the eye
? Have a basic understanding of the structure and functions of various
parts of the eye
? Orbit
Lodges the eyeball
? Eye lids ?
? Cover and protect
? Lacrimal system-
Secretes and drain tears
? Extraocular muscles-
for ocular movements
? Layers of eyeball-
perform various functions
Bony Orbit
? Made by 7
Bones:-
? Frontal
? Zygomatic
? Maxillary
? Ethmoidal
? Sphenoid
? Lacrimal
? Palatine
Frontal view of bony orbit
Outer eye: Eyelids
The eyelids fulfill two main
functions:
? protection of the eyeball
? secretion, distribution and
drainage of tears
The eyelid muscles
Lid structure and movement
The levator muscle extends from
an attachment at the orbital apex
to attachments at the tarsal
plate and skin.
The lids are securely attached at
either end to the bony orbital
margin by medial and lateral
palpebral ligaments.
Innervation
- Sensory innervation is from the trigeminal (fifth) cranial nerve, via
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
(third) nerve.
Blood supply
Network of blood vessels which form an anastomosis
between branches derived from the external carotid artery
via the face and from the internal carotid artery via the orbit.
Lymphatics
? Lymphatic fluid drains into the preauricular and submandibular nodes.
? Preauricular lymphadenopathy is a useful sign of infective eyelid
swelling (especially viral).
Lacrimal system
? Lacrimal gland
? Lacrimal passage
? Lacrimal puncta
? Lacrimal canaliculi
? Lacrimal sac
? Naso-lacrimal duct
Tear production
? The lacrimal gland secretes
most of the aqueous
component of the tear film
? Location: superotemporal
part of the anterior orbit
? Innervation :
parasympathetic fibres
carried by the facial nerve.
Lacrimal Apparatus/Drainage system
Extraocular muscles
? 4 Recti
? 2 Obliques
Medial rectus (MR)
Inferior Rectus (IR)
Superior rectus (SR)
Inferior oblique (IO)
Superior Oblique(SO)
Lateral Rectus (LR)
Extra-ocular muscles
? Action results in eye movements
? Medial Rectus --- Adduction
? Inferior Rectus ---
Depression,Extorsion,Adduction
? Superior Rectus ---
Elevation , Intorsion, Adduction
? Inferior Oblique---
Extorsion, Elevation, Abduction
? Superior Oblique---
Intorsion, Depression,Abduction
? Lateral Rectus --- Abduction
EXTRAOCULAR MUSCLES
Nerve supply of Extra Ocular Muscles
? Three Cranial Nerves supply the Extra Ocular Muscles
? CN 3rd-Oculomotor-MR, IR, SR, IO
? CN 4th-Trochlear--SO
? CN 6th- Abducens--- LR
Overview of ocular anatomy
Conjunctiva
? The conjunctiva is a mucous
membrane lining the eyelids.
Covers the anterior eyeball
up to the edge of the cornea.
? At the upper and lower
reflections between eyeball
and eyelid, conjunctiva forms
two sacs, the superior and
inferior fornices .
Cornea and sclera
The cornea and sclera form a
spherical shell which makes up
outer wall of eyeball.
Cornea and sclera
? The sclera is :
- principally collagenous,
- 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.
The cornea and sclera merge at the corneal edge (the limbus).
Limbus
? Juncture between the cornea and the sclera
? Nourishes peripheral cornea
? Assists in corneal wound healing
? Pathway for aqueous outflow (contains trabecular meshwork and
canal of schlemm)
Corneoscleral limbus
? Transition zone:
? anteriorbowman`s terminal-Descemet's terminal
? posteriorscleral spuriris root
? 1.52.0mm width
? Appearance
? Semitransparant zone
? White sclera
? Angle of AC
The chief functions of the cornea
? Protection against invasion of microorganisms into the eye
? Transmission and focusing (refraction) of light.
Cornea
? Made up of 5 layers
? Specialized Transparent Tissue
? No blood vessels
? Primarily responsible for refracting light (43-44 diopters)
? More nerve endings than anywhere else in the body
? Protection to the eye
? The only part of the eye that is transplanted from one person to
another
Cornea
? Epithelium
? Bowman membrane
? Stroma
? Descemet
membrane
(posterior limiting
layer of cornea)
? Endothelium
Cornea- 5 layered
Cornea
? Oval
? transverse11.512mm
? vertical10.511mm
? curvatureanterior 7.8mm
posterior6.8mm
? thicknesscentre0.50.55mm
periphery:1mm
? Refractive index1.377
Cornea
1.Epithelium
2.Bowman's membrane :
? 50m
? 12
? 5
m
6 layers
? Squamous cell
? No cell
? Basal cell
? Collagen matrix
? Renewing cycle7 days
? Scar
Cornea
3.Stroma
4. Descemet's membrane
? 500 m
? 1012 m
? 23 corneal cells
? No structure
? 1matrixGAGs)
? elasticity
? Fibrous lamina
? 200
? Secreted by endothelial cells
250 layers
? Parallel to surface
? Basal membrane of
endothelial cell
? Parallel collagen fibers
? Ordered arrangement
? Regeneration
? Scar
Cornea
5.Endothelium
? 5 m
? Monolayer hexagon
? 500 000 cells
? Tight junctions
? Pump
UVEA
? The uvea comprises the
? iris and ciliary body anteriorly
? choroid posteriorly
Iris
? Consists of connective tissue
containing muscle fibres, blood
vessels and pigment cells.
Its posterior surface is lined by a
layer of pigment cells.
At its centre is an aperture, the pupil.
The main function of pupil:
Control light entry to the retina and
to reduce intraocular light scatter.
Ciliary body
? The ciliary body is a specialised structure uniting the iris with the
choroid.
? Secretes aqueous humour
? Anchors the lens via the zonules, through which it modulates lens
convexity.
? The posterior part of the ciliary body merges into the retina at the ora
serrata.
Choroid
? The choroid, consisting of blood vessels, connective tissue and
pigment cells, is sandwiched between the retina and the sclera.
? It provides oxygen and nutrition to the outer retinal layers.
Lens
? The discus-like lens comprises
a mass of long cells known as
fibres. Has a hard nucleus
surrounded by less dense
fibres, the cortex.
? Relatively dehydrated
? Transparent.
Aqueous humour
? Fills the anterior and posterior chambers.
? 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.
They are connected by the pupil.
Formation
? The ciliary body forms
aqueous humour
? By ultrafiltration and
active secretion.
Drainage
Aqueous circulates from the
posterior to the anterior chamber
through the pupil.
Passes through the trabecular
meshwork (a specialised tissue in
the anterior chamber angle
between the iris and the cornea).
From here aqueous drains into
Schlemm's canal.
Vitreous
? A thick, transparent gel like substance that fills the center of
eyeball, giving it form and shape
? The vitreous body is 99% water but, vitally, also contains collagen
fibrils and hyaluronan, which impart cohesion and a gel-like
consistency.
? The vitreous is adherent to the retina at certain points,
particularly at the optic disc and at the ora serrata.
?
Volume - 4.5ml
?
RI:1.3360aqueous humor
Retina
? Innermost layer of the eye.
? Converts light energyelectrical energy --->brain via the optic nerve
? Composed of 10 layers.
? Contains Photoreceptors
? Cones-near Center (seeing detail and color)
? Rods- in Periphery (seeing in low light and movement)
Retina
?
Transparent ,thin
?
Anterior rimora serrata
?
3 parts:-
?
Peripheral Retina
?
Maculafovea
?
Optic disc
Retina
? Optic disc
? Only optic nerve fibers
? Physiological blind spot
? Macula
? Thinnest
? Point of sharpest vision is
in the fovea located in
the center of the macula
Histology of retina
1 RPE
2 Layers of Rods & Cones
3 External Limiting Membrane
4 Outer Nuclear layer
5 Outer Plexiform layer
6 Inner Nuclear layer
7 Inner Plexiform Layer
8 Ganglion Cell layer
9 Nerve Fibre layer
10 Internal limiting membrane
Retina
? The blood supply of the retina is derived from the central retinal
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
each of the retinal quadrants .
Optic nerve
? The ganglion cell axons in the retinal nerve fibre layer make a right-
angled turn into the optic nerve at the optic disc, which has no
photoreceptors 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
same membranous layers as the brain.
Optic Nerve Pathways/Visual Cortex
? Message is carried down the optic
nerve through pathways to
occipital cortex; here vision
becomes sight
? At the optic chiasm, the nasal
nerve fibers cross; temporal nerve
fibers go straight back to cortex;
this arrangement impacts on
visual fields
? Results in visual field losses can be
predicted based on where
damage is located on the optic
nerve
Conclusion
? The human eye is lodged inside bony orbit and protected by
eyelids.
? It has an outer protective scleral coat modified anteriorly to
form cornea
? The middle layer or uvea consists of the ciliary body and iris
anteriorly and choroid posteriorly
? The innermost layer is retina containing photoreceptors
which lines the posterior two-thirds of choroid.
? The optic nerve carries visual information to the visual cortex.
This post was last modified on 07 April 2022