Dr.Ali Muhye Aldeeen
1st lecture
Anatomy of Lid & Eye
Eyelids
They are divided into the following seven structural layers:
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Skin and subcutaneous tissue
orbicularis oculi muscle
Orbital septum
Orbital fat
Muscles of retraction
Tarsus
Conjunctiva
Eyelid skin is the thinnest of the body and unique in having no subcutaneous fat layer.
The upper eyelid crease approximates the attachments of the levator aponeurosis to the
pretarsal orbicularis bundles and skin.
The orbicularis oculi muscle is the main protractor of the eyelid. Contraction of this
muscle, innervated by cranial nerve VII, narrows the palpebral fissure. Specific portions
of this muscle also constitute the lacrimal pump. The orbicularis muscle is divided into
pretarsal, preseptal, and orbital parts.
The orbital septum, a thin multilayered sheet of fibrous tissue, arises from the
periosteum over the superior and inferior orbital rims at the arcus marginalis..
The tarsi are firm dense plates of connective tissue that serve as the skeleton of the
eyelids.The retractors of the upper eyelid are the levator muscle ( innervated by cranial
nerve III) with its aponeurosis and the sympathetically innervated superior tarsal muscle
(Muller's muscle). In the lower eyelid, the retractors are the capsulopalpebral fascia and
the inferior tarsal muscle.
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Dr.Ali Muhye Aldeeen
1st lecture
The eyelid can be devided into anterior and posterior lamellae by gray line. The anterior
lamella consist of skin and orbicularis. The posterior lamella consist of tarsus and
conjuctiva.
The lashes (cilia) are slightly more numerous in the upper (approximately 100) than in
the lower lid.
The lash roots lie against the anterior surface of the tarsus. The cilia pass between the
orbicularis oculi and the muscle of Riolan, exiting the skin at the anterior lid margin and
curve away from the globe.
Scarring of the tarsal plate and conjunctiva can alter their position and direction.
Following intense inflammation lashes may grow abnormally from meibomian gland
openings (distichiasis).
Meibomian glands are modified sebaceous glands located in the tarsal plates. They
empty through a single row of about 30 openings on each lid. A gland consists of a
central duct with multiple acini, the cells of which synthesize lipids (meibum) that pass
into the duct and form the outer layer of the precorneal tear film.
Glands of Zeis are modified sebaceous glands that are associated with lash follicles.
Glands of Moll are modified apocrine sweat glands which open either into a lash follicle
or directly onto the anterior lid margin between the lashes. They are more numerous in
the lower lid.
Lacrimal Drainage System
Anatomy
The puncta are located at the posterior edge of the lid margin, at the junction of the
lash-bearing lateral five-sixths (pars ciliaris) and the medial non-ciliated one-sixth (pars
lacrimalis). Normally they face slightly posteriorly and can be inspected by everting the
medial aspect of the lids.
Physiology
Tears secreted by the main and accessory lacrimal glands pass across the ocular surface.
A variable amount of the aqueous component of the tear film is lost by evaporation.
a. Tears flow along the upper and lower marginal strips (A) and enter the upper and
lower canaliculi by capillarity and also possibly by suction.
b. With each blink, the pretarsal orbicularis oculi compresses the ampullae, shortens
and compresses the horizontal canaliculi and moves the puncta medially.
Simultaneously, the lacrimal part of the orbicularis oculi, which is attached to the
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Dr.Ali Muhye Aldeeen
1st lecture
fascia of the lacrimal sac, contracts and compresses the sac, thereby creating a
positive pressure which forces the tears down the nasolacrimal duct and into the nose
(B and C).
c. When the eyes open the muscles relax, the canaliculi and sac expand creating a
negative pressure which, assisted by capillarity, draws the tears from the eye into the
empty sac
Lacrimal Gland
The lacrimal gland is composed of a larger orbital lobe and a smaller palpebral lobe.
The gland is located within a fossa of the frontal bone in the superior temporal orbit.
The lacrimal glands are exocrine glands, and they produce a serous secretion. The body
of each gland contains two cell types Acinar cells, which line the lumen of the gland
Myoepithelial cells, which surround the parenchyma and are covered by a basement
membrane
A variable number of thin-walled excretory ducts, blood vessels, lymphatics, and nerves
pass from the orbital into the palpebral lacrimal gland. The ducts continue downward,
and about 12 empty into the conjunctival fornix approximately 5 mm above the superior
margin of the upper tarsus.
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Dr.Ali Muhye Aldeeen
1st lecture
 Outer layer
o Cornea
o Sclera
o Corneoscleral junction: limbus
 Middle layer (uvea)
o Iris
o Ciliary body.
o Chroid
 Inner layer: retina
o Retinal pigment epithelium
o Sensory retina.
The adult human eye averages 24 mm in diameter.
Tear film constituents
The tear film has three layers
1. Lipid layer secreted by the meibomian glands.
It prevents evaporation of the aqueous layer and maintain tear film thickness.
2. Aqueous layer secreted by the lacrimal glands.
Functions:
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To provide atmospheric oxygen to the corneal epithelium.
Antibacterial activity due to proteins such as IgA, lysozyme and lactoferrin.
To wash away debris and noxious stimuli and allow the passage of leucocytes
after injury.
To provide a smooth optical surface to the cornea by abolishing minute
irregularities.
3. Mucous layer secreted principally by conjunctival goblet cells.
Functions
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To permit wetting by converting the corneal epithelium from a hydrophobic to a
hydrophilic surface.
Lubrication.
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Dr.Ali Muhye Aldeeen
1st lecture
The normal cornea is free of blood vessels; nutrients are supplied and metabolic
products removed mainly via the aqueous humour posteriorly and the tears anteriorly.
The cornea is the most densely innervated tissue in the body, with a subepithelial and a
deeper stromal plexus, both supplied by the 1st division of the trigeminal nerve
Dimensions
The average corneal diameter is 11.5 mm vertically and 12 mm horizontally. It is 540
µm thick centrally on average, and thicker towards the periphery.
The cornea consists of the following layers, each of which is critical to normal
function:
1. The epithelium is stratified squamous and non-keratinized.
2. Epithelial stem cells that are indispensable for the maintenance of a healthy
corneal surface are located principally at the superior and inferior limbus. They
also act as a junctional barrier, preventing conjunctival tissue from growing onto
the cornea.
3. Bowman layer is the acellular superficial layer of the stroma formed from
collagen fibres
4. The stroma makes up 90% of corneal thickness. It is arranged in regularly
orientated layers of collagen fibrils whose spacing is maintained by
proteoglycan ground substance with interspersed keratocytes. Maintenance of
the regular arrangement and spacing of the collagen is critical to optical clarity.
The stroma can scar, but cannot regenerate following damage.
5. Descemet membrane is a discrete sheet composed of a fine latticework of
collagen fibrils that are distinct from the collagen of the stroma. It serves as a
modified basement membrane for the endothelium.
6. The endothelium consists of a monolayer of polygonal cells. Endothelial cells
maintain corneal deturgescence throughout life by pumping excess fluid out of
the stroma. The adult cell density is about 2500 cells/mm2. The number of cells
decreases at about 0.6% per year and neighbouring cells enlarge to fill the space;
the cells cannot regenerate. At a cell density of about 500 cells/mm2 corneal
oedema develops and transparency is reduced.
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Dr.Ali Muhye Aldeeen
1st lecture
Sclera
Layers:
1. Episclera
2. Scleral stroma
3. Lamina fusca
 In contrast to the transparent cornea, the sclera is opaque and white. .
 The scleral stroma is composed of collagen bundles of varying size and shape
that are not as uniformly orientated as in the cornea.
 The inner layer of the sclera (lamina fusca) blends with the suprachoroidal
and supraciliary lamellae of the uveal tract. Anteriorly the episclera consists
of a dense, vascular connective tissue which lies between the superficial
scleral stroma and Tenon capsule.
 It is thinnest at the insertions of the rectus muscles (0.3 mm) and increases to
about 1 mm thick posteriorly.
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Dr.Ali Muhye Aldeeen
1st lecture
The transition zone between the peripheral cornea and the anterior sclera, known as the
limbus. It is 1.5 mm.
It cosist of the following:
1. Schwalbe line is the most anterior structure, appearing as an irregular opaque
line. Anatomically it demarcates the peripheral termination of Descemet
membrane and the anterior limit of the trabeculum.
2. The trabecular meshwork (TM) extends from Schwalbe line to the scleral
spur. The aqueous humor of the anterior chamber (A C) filters through the
TM to pass the canal of Schlemm and its collector veins. The TM is
composed of two portions: (1) a uveal meshwork that faces the AC (2) a
corneoscleral meshwork that is adjacent to the canal of Schlemm.
3. Schlemm canal is oval in cross section, that encircles the entire
circumference of the AC.
4. The scleral spur is the most anterior projection of the sclera and the site of
attachment of the longitudinal muscle of the ciliary body.
5. The ciliary body stands out just behind the scleral spur as a pink to dullbrown to slate-grey band.
Conjunctiva
Anatomy
 The conjunctiva is a transparent mucous membrane lining the inner surface of the
eyelids and the surface of the globe as far as the limbus.
 It is richly vascular, supplied by the anterior ciliary and palpebral arteries.
 There is a dense lymphatic network, with drainage to the preauricular and
submandibular nodes.
 It has a key protective role, mediating both passive and active immunity.
It is subdivided into the following:
1. The palpebral conjunctiva starts at the mucocutaneous junction of the lid margins.
2. The forniceal conjunctiva is loose and redundant and may be thrown into folds.
3. The bulbar conjunctiva covers the anterior sclera and is continuous with the
corneal epithelium at the limbus. The stroma is loosely attached to the underlying
Tenon capsule, except at the limbus, where the two layers fuse.
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Dr.Ali Muhye Aldeeen
1st lecture
A plica semilunaris (semilunar fold “P”) is present nasally, medial to which lies a fleshy
nodule (caruncle “C”) consisting of modified cutaneous tissue containing hair follicles,
accessory lacrimal glands, sweat glands and sebaceous glands.
Histology
1. The epithelium is non-keratinizing and around five cell layers deep. Basal cuboidal
cells evolve into flattened polyhedral cells before they are shed from the surface.
Goblet cells are located within the epithelium and are densest inferonasally and in the
fornices.
2. The stroma (substantia propria) consists of richly vascularized loose connective
tissue. The adenoid superficial layer does not develop until about 3 months after
birth, hence the inability of the newborn to produce a follicular conjunctival reaction.
The deep fibrous layer merges with the tarsal plates. The accessory lacrimal glands of
Krause and Wolfring are located deep within the stroma. Mucus from the goblet cells
and secretions from the accessory lacrimal glands are essential components of the
tear film.
Uveal Tract
The uveal tract is the main vascular compartment of the eye.
Iris: the iris is the most anterior extension of the uveal tract. The iris diaphragm
subdivides the anterior segment into the anterior and posterior chambers.
It is made up of.
1. Stroma:
It is located anteriorly and composed of blood vessels and connective tissue, in
addition to the melanocytes and pigment cells that are responsible for its distinctive
color. The stroma of blue irides is lightly pigmented, and brown irides have a
densely pigmented stroma that absorbs light.
The sphincter pupillae muscle ( parasympathetics 3 CN ) is located in the pupillary
zone of the posterior stroma. It is responsible for miosis ( pupillary constriction). The
dilator pupillae muscle ( sympathetics) extends from the iris root at the ciliary body
as far as sphincter pupillae muscle. It is responsible for mydriasis ( pupillary
diltation).
2. Posterior Pigmented Layer
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Dr.Ali Muhye Aldeeen
1st lecture
Ciliary Body
The ciliary body, which is triangular in cross section, bridges the anterior and posterior
segments. The apex of the ciliary body is directed posteriorly toward ora serrata. It has
two principal functions: aqueous humor formation and lens accommodation.
Ciliary Epithelium and Stroma
The ciliary body is 6-7 mm wide and consists of two parts: the pars plana (4 mm)
posteriorly and the pars plicata (2mm) anteriorly. The pars plicata is richly vascularized
and consists of approximately 70 ciliary processes. The zonular fibers of the lens attach
primarily in the valleys of the ciliary processes but also along the pars plana. The ciliary
body is lined by a double layer of epithelial cells, the inner nonpigmented and the outer
pigmented epithelium.
Ciliary Muscle
It has three layers of fibers (from out to in):
1. Longitudinal
2. Radial
3. Circular: their contraction relaxes the lens zonule, which allows the greater
curvature of the lens, thereby increasing its refractive power ( accommodation)
Choroid
The choroid, the posterior portion of the uveal tract, nourishes the outer portion of the
retina. It averages 0.25 mm in thickness and consists of three layers of vessels:
1. The choriocapillaris, the innermost layer
2. A middle layer of small vessels
3. An outer layer of large vessels
Perfusion of the choroid comes from both the long and the short posterior ciliary arteries
and from the perforating anterior ciliary arteries. venous blood drain through the vortex
system.
Blood flow through the choroid is high compared to other tissues. As a result, the
oxygen content of the choroidal venous blood is only 2%-3% less than that of the
arterial blood.
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Dr.Ali Muhye Aldeeen
st
11st
lecture
lecture
Lens
The crystalline lens is a transparent, biconvex structure whose functions are
1. To maintain its own clarity
2. To refract light
3. To provide accommodation
The lens has no blood supply or innervation after fetal development, and it depends
entirely on the aqueous humor to meet its metabolic requirements and to carry off its
wastes. It lies posterior to the iris and anterior to the vitreous body. It is suspended in
position by the zonules of Zinn, consisting of delicate yet strong fibers that support and
attach it to the ciliary body. The lens is composed of the capsule, lense pithelium,
cortex, and nucleus. The adult lens typically measures 9 mm equatorially and 5 mm
anteroposteriorly
The Vitreous
Occupying 80% of the volume of the eye, the vitreous is a clear matrix composed of
collagen, hyaluronic acid, and water. It is bounded anteriorly by the posterior lens
capsule and posteriorly by the the retina.
The retina can be devide mainly in to
 Outer part, the retinal pigment epithelium (RPE) is composed of a single layer
of cells.
 Inner part, the neurosensory retina is composed of 9 layers.
Subretinal space is a potential space between RPE and neurosensory retina.
Blood supply:
The choroid supply RPE and outer part of neurosensory retina, while centeral retinal
artery suplly the inner part of neurosensory retina.
Macula
 It is a round area at the posterior pole, lying inside the temporal vascular arcades. It
measures between 5 and 6 mm in diameter. Histologically, it shows more than one
layer of ganglion cells, in contrast to the single ganglion cell layer of the peripheral
retina. It contains xanthophyll (yellow) pigment.
 The fovea is a depression in the retinal surface at the centre of the macula, with a
diameter of 1.5 mm (B), about the same as the optic disc.
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Dr.Ali Muhye Aldeeen
1st lecture
 The foveola forms the central floor of the fovea and has a diameter of 0.35 mm
(C).
 The umbo is a depression in the very centre of the foveola which corresponds to
the foveolar light reflex.
 The foveal avascular zone (FAZ), a central area containing no blood vessels but
surrounded by a continuous network of capillaries, is located within the fovea but
extends beyond the foveola.
There are two types of photoreceptor cells:
1. The rods are the most numerous (120 million) and are of the highest
concentration in the mid-peripheral retina. They are most sensitive in dim
illumination and are responsible for night and peripheral vision.
2. The cones are fewer in number (6 million) and have their highest
concentration at the fovea. They are most sensitive in bright light and mediate
day vision, colour vision and central visual acuity
Optic nerve
Afferent fibres.
The optic nerve carries approximately 1.2 million afferent nerve fibres which originate
in the retinal ganglion cells. Most of these synapse in the lateral geniculate body,
although some reach other centres, notably the pretectal nuclei in the midbrain.Within
the optic nerve itself the nerve fibres are divided into about 600 bundles, each
containing 2000 fibres, by fibrous septae derived from the pia mater.
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Dr.Ali Muhye Aldeeen
1st lecture
Surrounding sheaths
The innermost sheath is the delicate vascular pia
mater.
The outer sheath comprises the arachnoid mater and the tougher dura mater which is
continuous with the sclera. The subarachnoid space is continuous with the cerebral
subarachnoid space and contains cerebrospinal fluid (CSF).
The optic nerve is approximately 50 mm long from globe to chiasm.
The nasal retinal elements project into the temporal field, upper retinal elements project
into the lower field and vice versa.
The optic pathways projected onto the base of the brain. All axons that orginate from
ganglion cells located on the nasal side of a line passing through the center of the fovea
decussate ( cross ) at the optic chiasm. The nasal fibers join uncrossed axons from the
temporal half of each retina to from the opic tract.
Axons carrrying visual impulses synapse in the lateral geniculate bodies with the cells
whose axons form the optic radiation.
The centeral retina is represented posteriorly in the visual cortex, while the peripheral
retina is represented anteriorly in the visual cortex.
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Dr.Ali Muhye Aldeeen
1st lecture
Extraocular muscle
1. Lateral rectus (LR) is supplied by the 6th cranial nerve (abducent nerve –
abducting muscle).
2. Superior oblique (SO) is supplied by the 4th cranial nerve (trochlear nerve –
muscle associated with the trochlea). It is resposible for depression and
intorsion .
3. Medial rectus ( MR: adduction ), inferior oblique ( IO: elevation and
extorsion ), inferior rectus ( IR: depression ) and the ciliary and sphincter
pupillae muscles are supplied by the third (oculomotor) nerve.
Good luck
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