Download MBBS Ophthalmology PPT 37 Ocular Anatomy Lecture Notes

Ocular Anatomy

Department of Ophthalmology

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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)

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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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? Orbit
Lodges 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 tarsal

plate 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 aqueous

component of the tear film

? Location: superotemporal

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part of the anterior orbit

? Innervation :

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parasympathetic fibres

carried by the facial nerve.

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Lacrimal Apparatus/Drainage system

Extraocular muscles

? 4 Recti

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? 2 Obliques
Medial 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 MUSCLES
Nerve 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 eyeball

up 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 and

inferior 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 and
canal 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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? Descemet

membrane

(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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Cornea

3.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, blood

vessels 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 ora

serrata.

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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 the

posterior 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 angle

between 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-like

consistency.

? 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 is

in 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 & Cones

3 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 Layer

8 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 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

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same membranous layers as the brain.


Optic Nerve Pathways/Visual Cortex

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? Message is carried down the optic

nerve 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 nerve

fibers 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 where

damage 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 iris

anteriorly 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.