1. ORBIT

2. ORBIT
Introduction
 are bilateral bony cavities in the facial skeleton, situated one on each
side of the root of the nose
Shape
It resembles a hollow quadrangular pyramid
Functions
It contain and protect the;
 eyeballs
 associated visceral structures
These associated visceral structures include:
 Eyelids
 Extraocular muscles
 Nerves and vessels in transit to the eyeballs and muscles
 Orbital fascia surrounding the eyeballs and muscles

3.  Mucous membrane (conjunctiva) lining the eyelids and
anterior aspect of the eyeballs
 lacrimal apparatus
 Orbital fats
 Seven bones form the bony orbit namely;
• Maxilla
• Zygomatic
• Lacrimal
• Ethmoid
• Palantine
• Sphenoid
• Frontal
3

4. Boundaries
 The pyramidal orbit has;
 an apex
 a base
 and four walls; superior, inferior, medial, lateral
Apex : is the optic canal (foramen)
Base of the orbit
Is the orbital rim (margin)
It is formed;
• Superior margin: frontal bone
• Medial margin: maxilla
• Inferior margin: zygomatic bone, maxilla
• Lateral margin: frontal process of the zygomatic bone, zygomatic
process of the frontal bone

5. The orbit is a pyramidal cavity with its base in front and its apex
behind

7. Four walls

•

•
•

•
•
•
•
The superior wall (roof):
formed mainly by the orbital part of the frontal bone
The medial wall:
formed by orbital parts of the ethmoid bone, lacrimal and frontal
bones
it is indented anteriorly by the lacrimal groove and fossa for the
lacrimal sac
The inferior wall (floor):
formed mainly by the maxilla (orbital part) and partly by the orbital
parts of the zygomatic and palatine bones
It is demarcated from the lateral wall of the orbit by the inferior
orbital fissure
The lateral wall: formed by the orbital parts of zygomatic bone and
greater wing of the sphenoid
This is the strongest and thickest wall, which is important because it
is most exposed and vulnerable to direct trauma

8. note
• the orbit communicates with;
 the middle cranial fossa (via the optic canal and superior
orbital fissure)
 the infratemporal and pterygopalatine fossae (via the
inferior orbital fissure)
 the inferior meatus of the nose (via the nasolacrimal
canal)
 the nasal cavity (via the anterior ethmoidal foramen),
 and the face (via supraorbital and infraorbital foramina)

12. Eyelids
• They are movable folds that are covered externally by thin skin and
internally by transparent mucous membrane
functions
 When closed, the eyelids cover the eyeball anteriorly, thereby
protecting it from injury and excessive light
 They also keep the cornea moist by spreading the lacrimal fluid
Conjuctiva
• The internal transparent mucous membrane of the eyelid is the
palpebral conjunctiva
• The palpebral conjunctiva is reflected onto the eyeball and it is
continuous with the bulbar conjunctiva
• The bulbar conjunctiva is thin and transparent and attaches loosely to
the anterior surface of the eyeball
• The bulbar conjunctiva lies over the sclera and is adherent to the
periphery of the cornea, it contains visible small blood vessels

16. • When the eyelids are closed, a closed space is formed in between the
palpebral and bulbar conjunctivae
• This space is called the conjunctival sac
• The conjunctival sac opens through an anterior aperture, called the
palpebral fissure (the gap between the eyelids), when the eyelids are
parted
• The upper and lower extensions of this sac are the superior and
inferior conjunctival fornices (singular: fornix)
Clinical anatomy
 Hyperemia of the Conjunctiva
• The conjunctiva is colorless, except when its vessels are dilated and
congested causing hyperemia
• Hyperemia of the conjunctiva is caused by local irritation (e.g., from
dust, chlorine, or smoke)
 An inflamed conjunctiva (conjunctivitis/ pink eye) is a common
contagious infection of the eye

17. of the conjuctiva

20. Skeleton of the eyelids
• The superior (upper) and inferior (lower) eyelids are strengthened
by dense bands of connective tissue called the superior and inferior
tarsi (singular: tarsus)
• The superior and inferior tarsi form the skeleton of the eyelids
• Embedded in the tarsi are tarsal glands/ meibomial glands
• The tarsal glands;
 provide the lipid secretion of which lubricates the edges of the
eyelids and prevents them from sticking together when they close
 The lipid secretion also forms a barrier that lacrimal fluid does not
cross when produced in normal amounts
• When production is excessive, it spills over the barrier onto the
cheeks as tears

25. Clinical anatomy
chalazion
• a small, nonmalignant, localized swelling of the eyelid resulting
from obstruction and retained secretions of the meibomian glands

26. Eyelashes are the hairs that grow on margins of the lids
• The superior and inferior eyelids meet at angles called the medial
and lateral palpebral commissures, or medial and lateral canthi
(singular: canthus)
• Between the nose and the medial angle of the eye is the medial
palpebral ligament, which connects the tarsi to the medial margin
of the orbit
• The orbicularis oculi originates and inserts onto this ligament
• A similar lateral palpebral ligament attaches the tarsi to the lateral
margin of the orbit but does not provide for direct muscle
attachment

30. Lacrimal Apparatus
• is involved in the production, movement, and drainage of fluid from
the surface of the eyeball
It is made up of the;
• lacrimal gland
• lacrimal ducts
• lacrimal canaliculi
• lacrimal sac
• nasolacrimal duct
Lacrimal gland
Intro:
• almond shaped
• approximately 2 cm long
Location:
• lies in the fossa for the lacrimal gland in the superolateral part of
each orbit

31. Parts:
It is divided into;
• superior (orbital) part
• inferior (palpebral) part by the lateral expansion of the tendon of
the levator palpebrae superioris
Function:
• secrete lacrimal fluid, a watery physiological saline containing the
bacteriocidal enzyme lysozyme
• The fluid;
1. moistens and lubricates the surfaces of the conjunctiva and cornea
2. provides some nutrients and dissolved oxygen to the cornea
• When the fluid is produced in excess, it constitutes tears
 Note;
Accessory lacrimal glands are also present; they are more numerous
in the superior eyelid than in the inferior eyelid

37. Lacrimal ducts:
• convey lacrimal fluid from the lacrimal glands to the conjunctiva
sac
Lacrimal canaliculi:
• commence at a lacrimal punctum (opening) on the lacrimal papilla
near the medial angle of the eye and drain lacrimal fluid from the
lacrimal lake
• a triangular space at the medial angle of the eye where the tears
collect) to the lacrimal sac (the dilated superior part of the
nasolacrimal duct)
 Note: the lacrimal papilla is a slight projection from the margin of
each eyelid near the medial commissure, in the center of which is
the lacrimal puntum (operning of the lacrimal duct)
Nasolacrimal duct:
• conveys the lacrimal fluid to the inferior nasal meatus

38. CLINICAL ANATOMY
 Injury to the Nerves Supplying the Eyelids
• The oculomotor nerve supplies the levator palpebrae superioris, a
lesion of the oculomotor nerve causes paralysis of the muscle, and
the superior eyelid droops (ptosis)
• Damage to the facial nerve involves paralysis of the orbicularis
oculi, preventing the eyelids from closing fully
Drooping eyelid

39. The Eyeball
 The eyeball contains the optical apparatus of the visual system and
occupies most of the anterior portion of the orbit.
Layers:
 The eyeball proper has 3 layers:
 Fibrous layer (outer coat), consisting of the sclera and cornea
 Vascular layer (middle coat), consisting of the choroid, ciliary body,
and iris
 Inner layer (inner coat), consisting of the retina that has both optic
and non-visual parts
 however, there is an additional loose connective tissue layer that
surrounds the eyeball
 This loose connective tissue layer is composed
 posteriorly of bulbar fascia, which forms the true socket for the
eyeball
 and anteriorly of bulbar conjunctiva

40. Fibrous Layer of the Eyeball
 The sclera:
• is the tough opaque part of the fibrous layer (coat) of the eyeball
• It covers the posterior 5/6 of the eyeball
• It is the fibrous skeleton of the eyeball, providing shape and resistance
as well as attachment for both the extrinsic (extraocular) and the
intrinsic muscles of the eye
• The anterior part of the sclera is visible through the transparent
bulbar conjunctiva as the white of the eye
 The cornea:
• is the transparent part of the fibrous coat
• covers the anterior 1/6 of the eyeball
Note: While the sclera is relatively avascular, the cornea is
completely avascular, receiving its nourishment from ;
 capillary beds around its periphery
 Lacrimal fluids on its external surface
 and the aqueous humour on the internal surface

44. Vascular Layer of the Eyeball
• also called the uvea or uveal tract
 consists of the:
 choroid
 ciliary body
 iris
The choroid:
• a dark reddish brown layer between the sclera and the retina
• It is a highly vascular layer (presence of large vessels and fine
vessels called the capillary lamina of the choroid, or
choriocapillaris)
• forms the largest part of the vascular layer of the eyeball and
lines most of the sclera
• It is continuous anteriorly with the ciliary body
• The choroid attaches firmly to the pigment layer of the retina, but
it can easily be stripped from the sclera

45. The ciliary body :
• is muscular and vascular
• connects the choroid with the circumference of the iris
• The ciliary body provides attachment for the lens
• contraction and relaxation of the smooth muscle of the ciliary body
controls thickness (and therefore the focus) of the lens
• Folds on the internal surface of the ciliary body called the ciliary
processes, secrete aqueous humor
• The aqueous humor fills the anterior and posterior chambers of the
eye
• The anterior chamber of the eye is the space between the cornea
anteriorly and the iris/pupil posteriorly
• The posterior chamber of the eye is between the iris/pupil
anteriorly and the lens and ciliary body posteriorly

48. The iris:
• lies on the anterior surface of the lens
• is a thin contractile diaphragm with a central aperture, called the
pupil, for transmitting light
• the size of the pupil varies continually to regulate the amount of light
entering the eye
 Two involuntary muscles control the size of the pupil:
• the parasympathetically stimulated sphincter pupillae constrict/
decrease the diameter of the pupil
• the sympathetically stimulated dilator pupillae dilate or increases the
diameter of the pupil
Clinical anatomy
Uveitis
• inflammation of the vascular layer of the eyeball (uvea), may
progress to severe visual impairment and blindness

49. Inner Layer of the Eyeball
 The inner layer of the eyeball is the retina
it consists of two functional parts:
• an optic part: which is posterior and lateral and is sensitive to light
• a non-visual retina: which is anterior and covers the internal surface
of the ciliary body and the iris
• The junction between these parts is an irregular line called the ora
serrata
 Note: The ora serrata marks the anterior termination of the lightreceptive part of the retina
The optic part of the retina :
 is sensitive to visual light rays
 has two layers:
 an outer pigmented layer
 an inner neural layer

51. The non-visual retina :
• is an anterior continuation of the outer pigmented layer
• a layer of supporting cells over the ciliary body (ciliary part of the
retina)
• the posterior surface of the iris (iridial part of the retina)
•
•
•
•
•
Ocular fundus/ fundus of the eyeball
This is the internal aspect of the posterior part of the eyeball,
where light entering the eyeball is focus
it includes the retina, optic disc, macula and fovea
has a circular depressed area called the optic disc (optic papilla)
The optic disc is where the optic nerve leaves the retina
branches of the central retinal artery spread from this point
outward to supply the retina

53. • the optic disc is insensitive to light
• This is because it contains no photoreceptors (no rods and cones)
• This part of the retina is commonly called the blind spot
• Just lateral to the optic disc is a small area with a hint of yellowish
coloration called macula lutea (yellow spot)
• It has a central depression called the fovea centralis
• This is the thinnest area of the retina and visual sensitivity here is
higher than elsewhere in the retina
• This is because it has fewer rods and more cones
Rods and Cones
• The rods and cones are the light receptors of the eye
• They are sensitive to colour
• The rods contain a pigment called visual purple
• They can respond to dim light (scotopic vision)
• The cones respond only to bright light (photopic vision)

55. Refractive Media of the Eyeball
The Refractive Media of the Eyeball is made up of 4 parts;
 cornea
 aqueous humor,
 lens
 vitreous humor
Cornea:
• is the circular area of the anterior part of the outer fibrous layer of
the eyeball
• it is largely responsible for refraction of the light that enters the eye
• It is transparent and sensitive to touch
• its innervation is provided by the ophthalmic nerve (CN V1).
• It is avascular
• Its nourishment is derived from the capillary beds at its periphery,
the aqueous humor, and lacrimal fluid
• The lacimal fluid also provides oxygen absorbed from the air

58. Aqueous humor :
• It is located in the anterior and posterior chambers of the eye
• produced in the posterior chamber by the ciliary processes of the
ciliary body
• This clear watery solution provides nutrients for the avascular
cornea and lens
• After passing through the pupil into the anterior chamber, the
aqueous humor drains through a trabecular meshwork into the
scleral venous sinus / Schlemm canal) at the iridocorneal angle
• From the schlemm canal it drains into the anterior ciliary veins
and vorticose veins
Lens:
• is posterior to the iris and anterior to the vitreous humor of the
vitreous body
• It is a transparent, biconvex structure enclosed in a capsule
• is anchored by the zonular fibers (suspensory ligament of the lens)
to the ciliary body

61. • Although most refraction is produced by the cornea, the
convexity of the lens, particularly its anterior surface,
constantly varies to fine-tune the focus of near or distant
objects on the retina
• The ciliary muscle in the ciliary body changes the shape of
the lens
 parasympathetic stimulation;
• causes the smooth muscle of the ciliary body to contract
• Making the tension on the lens to be reduced/ zonular fibers
relax
• allowing the lens to become more spherical
• The increased convexity makes its refraction suitable for
near vision

62. In the absence of parasympathetic stimulation
• the ciliary muscles relax again
• Tension on the lens is increased/ zonular fibers
contract
• lens becomes flattened
• The decreased convexity makes its refraction
suitable for far vision
 The ability of the lens to focus on both near and
far vision is called accommodation

65. vitreous humor:
• is a watery fluid enclosed in the meshes of the vitreous body
• a transparent jelly-like substance in the posterior four fifths of the
eyeball posterior to the lens (postremal or vitreous chamber, or
posterior segment).
• In addition to transmitting light, the vitreous humor holds the retina in
place and supports the lens
CLINICAL ANATOMY
 Corneal Abrasions and Lacerations
• Foreign objects such as sand or metal filings (particles) produce
corneal abrasions that cause sudden, stabbing pain in the eyeball and
tears. Opening and closing the eyelids is also painful
• Corneal lacerations are caused by sharp objects such as fingernails
or the corner of a page of a book

66.  Presbyopia
• As people age, their lenses become harder and more flattened
• These changes gradually reduce the focusing power of the lenses, a
condition known as presbyopia
 Cataracts
• is a clouding of the lens inside the eye which leads to a decrease in
vision
• Visual loss occurs because opacification of the lens obstructs light
from passing and being focused on to the retina at the back of the eye
• It is the most common cause of blindness and is conventionally treated
with surgery
• Cataract extraction is a common operation
 Hemorrhage into the Anterior Chamber
• Hemorrhage within the anterior chamber of the eyeball (hyphema or
hyphemia) usually results from blunt trauma to the eyeball, such as
from a squash or racquet ball or a hockey stick

68. •
Initially, the anterior chamber is tinged red but blood soon
accumulates in this chamber
• The initial hemorrhage usually stops in a few days and recovery is
usually good
Glaucoma
• When drainage of aqueous humor through the scleral venous sinus
into the blood circulation decreases significantly, pressure builds
up in the anterior and posterior chambers of the eye, a condition
called glaucoma
• Blindness can result from compression of the inner layer of the
eyeball (retina) and the retinal arteries if aqueous humor
production is not reduced to maintain normal intraocular pressure

70.  Coloboma (defect)
• is a hole in one of the structures of the eye, such as
the iris, retina, choroid or optic disc
• The hole is present from birth and can be caused when a gap
called the choroid fissure, which is present during early stages of
prenatal development, fails to close up completely before a child is
born
Coloboma of Iris
• The absence of a section of iris may result from a birth defect, in
which the choroid fissure fails to close properly, from penetrating
or non-penetrating injuries to the eyeball, or a surgical iridectomy
• When the iris is injured in such a manner, the iridial fissure does
not heal

71. Coloboma of the iris

72. Muscles of the orbit
 There are 2 groups of muscles within the orbit:
 intrinsic muscles of the eyeball
 extrinsic muscles of eyeball (extra-ocular muscles)
 The intrinsic muscles within the eyeball control;
• the shape of the lens
• size of the pupil
These include;
• ciliary muscle
• sphincter pupillae,
• dilator pupillae
 The extrinsic muscles of eyeball (extra-ocular muscles) are
responsible for;
• raising upper eyelids
• movements of the eyeball

73. Extraocular Muscles of the Orbit
 The extraocular muscles of the orbit are 7 in number, and they
include the:
 levator palpebrae superioris
 four recti, which are;
I. Superior rectus
II. inferior rectus
III. Medial rectus
IV. and lateral rectus
 and two obliques, which are;
I. superior oblique
II. and inferior oblique
• Of the seven muscles in the extrinsic group of muscles, one raises
the superior eyelids, whereas the other six move the eyeball itself

75. Muscle
Origin
Insertion
Innervation
Action
Levator palpebrae Lesser wing of
Superior tarsus and Oculomotor nerve Elevation of upper
superioris
sphenoid anterior skin of superior
(CN III)
eyelid
to optic canal
eyelid
Superior rectus
Superior part of
Anterior half of
common tendinous eyeball superiorly
ring
Oculomotor nerve Elevates, adducts,
(CNIII)
and rotates eyeball
medially
Inferior rectus
Inferior part of
Anterior half of
common tendinous eyeball inferiorly
ring
Oculomotor nerve Depresses, adducts,
(CN III)
and rotates eyeball
laterally
Medial rectus
Medial part of
Anterior half of
common tendinous eyeball medially
ring
Oculomotor nerve Adduction of
(CN III)
eyeball
Lateral rectus
Lateral part of
Anterior half of
common tendinous eyeball laterally
ring
Abducent nerve
(CNVI)
Abducts eyeball

76. Superior oblique Body of sphenoid tendon passes
bone
through a fibrous
ring or trochlea,
changes its
direction, and
inserts into sclera
deep to superior
rectus muscle
Inferior oblique Anterior part of Sclera deep to
floor of orbit
lateral rectus
muscle
Trochlear nerve
(CN IV)
Abducts,
depresses, and
medially rotates
eyeball
Oculomotor nerve Abducts, elevates,
(CNIII)
and laterally
rotates eyeball

83. • Medial movement of the superior pole of the eyeball is intorsion;
• lateral movement of the superior pole is extorsion.
• These movements accommodate changes in the tilt of the head.
• Absence of these movements resulting from nerve lesions contributes to
double vision
Innervation of muscles of eyeball
• The oculomotor (CN III), trochlear (CN IV), and abducent (CN VI) nerves
are distributed to the muscles of the eyeball
• The nerves enter the orbit through the superior orbital fissure.
• CN IV supplies the superior oblique,
• CN VI supplies the lateral rectus,
• and CN III supplies the remaining five muscles
NOTE:
 All muscles of the orbit are supplied by CN III, except for the superior
oblique and lateral rectus, which are supplied by CN IV and VI, respectively
 (Memory device: LR6SO4AO3; lateral rectus, CN VI; superior oblique, CN
IV; all others, CN III

84. Fascial Sheath of the Eyeball
• It is also called Tenon’s capsule or the bulbar sheath
• It envelops the eyeball from the optic nerve nearly to the
corneoscleral junction, forming the actual socket for the eyeball
• The fascial sheath is pierced by the tendons of the extraocular
muscles
• A potential space exist between the eyeball and the fascial sheath
called the episcleral space and its allows the eyeball to move inside
the cup-like sheath

87. ARTERIAL SUPPLY TO THE ORBIT
Arterial supply to the structures in the orbit, including the eyeball, is
mainly by the ophthalmic artery
• it is a branch of the internal carotid artery
• The ophthalmic artery passes into the orbit through the optic canal
with the optic nerve
• In the orbit the ophthalmic artery initially lies inferior and lateral to
the optic nerve
• it passes forward and crosses superior to the optic nerve and
proceeds anteriorly on the medial side of the orbit
• In the orbit the ophthalmic artery gives off numerous branches as
follows:
 lacrimal arteries
 central retinal artery
 long and short posterior ciliary arteries

88. 



supra-orbital artery
posterior ethmoidal artery
anterior ethmoidal artery
medial palpebral arteries, which are small branches supplying the
medial area of the upper and lower eyelids
 dorsal nasal artery
 supratrochlear artery
Venous drainage
 There are two venous channels in the orbit,
• the superior ophthalmic vein
• and inferior ophthalmic vein
 The central vein of the retina usually enters the cavernous sinus
directly, but it may join one of the ophthalmic veins

90. 
•

•
CLINICAL ANATOMY
Injury to the Nerves Supplying the Superior Eyelids
The oculomotor nerve supplies the levator palpebrae superioris, a lesion of
the oculomotor nerve causes paralysis of the muscle, and the superior
eyelid droops (ptosis)
Oculomotor Nerve Palsy
Complete oculomotor nerve palsy affects most of the ocular muscles, the
levator palpebrae superioris, and the sphincter pupillae
 Abducent nerve palsy causes paralysis to the lateral rectus
 Blockage of the Central Vein of the Retina
• Because the central vein of the retina enters the cavernous sinus,
thrombophlebitis of this sinus may result in the passage of a thrombus to
the central retinal vein and produce a blockage in one of the small retinal
veins
• Occlusion of a branch of the central vein of the retina usually results in
slow, painless loss of vision

91.  Blockage of the Central Artery of the Retina
• Because terminal branches of the central artery of the retina are end
arteries, obstruction of them by an embolus results in instant and
total blindness
• Blockage of the artery is usually unilateral and occurs in older
people