The orbit is a pyramid-shaped cavity in the skull that houses the eyeball and surrounding structures. It is formed by 7 bones and has 4 walls - medial, lateral, roof and floor. The orbit contains the eyeball, extraocular muscles, nerves, vessels, fat and fascia. At the back of the orbit are the optic canal and superior orbital fissure, which transmit nerves and vessels to and from the orbit. The base of the orbit has openings that allow communication between the orbital and eyelid spaces.

1. THE ORBIT
BY - MS. MEGHNA VERMA
ASSISTANT PROFESSOR
DEPARTMENT OF OPTOMETRY
RAMA UNIVERSITY

2. CONTENTS
• Introduction [size, shape, relations]
• Walls of orbit
• Base or orbit
• Apex of orbit
• Periorbita
• Orbital fascia
• Fascia bulbi
• Orbital fat and reticular tissue
• Aperture at the base of the orbit
• Surgical space in the orbit
• Contents of the orbit

3. INTRODUCTION
The orbits are conical or four-sided pyramidal cavities, which open into
the midline of the face and point back into the head. Each consists of a
base, an apex and four walls.[4]
Each orbit is formed by seven bones –
1) Frontal bone
2) Ethmoidal bone
3) Lacrimal bone
4) Palatine bone
5) Maxilla bone
6) Zygomatic bone
7) Sphenoid bone

5. • The medial walls of two orbit are parallel to each other.
• They are in contact with the sphenoid bone & ethmoid bone.
• The depth of the orbits is 42mm along to medial wall & 50mm
along the lateral wall.
• Base of orbit is 40 mm in width & 35 mm in height.
• The intra orbital width [b/w the medial margin of two orbit] is
25mm.
• The extra orbital width [b/w the lateral margin of two orbit] is
100mm.

6. WALLS OF THE ORBIT
The bony orbit has 4 walls –
1. Medial wall
2. Lateral wall
3. Roof
4. Floor

7. MEDIAL WALL
The medial wall is formed primarily by the orbital plate of ethmoid, as well as
contributions from the frontal process of maxilla, the lacrimal bone, and a small part of the
body of the sphenoid. It is the thinnest wall of the orbit, evidenced by pneumatized
ethmoidal cells.[7]
The anterior part of medial wall – lacrimal sac fossa
Lacrimal fossa attached, inferiorly - naso-lacrimal canal.
anteriorly - anterior lacrimal crest
posteriorly – posterior lacrimal crest.
 Behind the posterior lacrimal crest – fibres of orbicularis muscle, orbital septum
and medial rectus muscle ligaments.
Medial part of medial wall – anterior ethmoidal sinus, middle ethmoidal sinus and
posterior ethmoidal sinus and sphenoid sinus.
 In it, SO & MR muscle, b/w two muscles situated anterior and posterior ethmoidal
nerve, ophthalmic artery and infratrochlear nerve.

8. LATERAL WALL
 It is triangular in shape.
 It is bounded anteriorly by zygomatic bone and posteriorly by sphenoid bone.
 Anterior part of lateral wall – zygomatic groove.
 Posterior part of lateral wall - lateral rectus muscle.
 Lateral part of lateral wall - lateral rectus muscle lacrimal nerve and vessels and
zygomatic nerves.

9. SUPERIOR WALL [ROOF]
 It is triangular in shape.
 The roof (superior wall) is formed primarily by the orbital plate frontal
bone, and also the lesser wing of sphenoid near the apex of the orbit.
The orbital surface presents medially by trochlear fovea and laterally by
lacrimal fossa.[7]
 Above the roof – cerebrum and meninges.
 Below the roof – periorbita, frontal nerves, LPS muscle, superior rectus,
lacrimal gland, trochlear nerve.
 Antero-lateral part of the roof has a fossa, called lacrimal gland fossa.
 b/w medial wall and roof has a superior oblique fossa, ethmoidal sinus.
 b/w lateral wall and roof has a superior orbital fissure [space].

10. INFERIOR WALL [FLOOR]
It is triangular in shape.
It is formed by 3 bones – medially maxilla bone, laterally zygomatic bone
and posteriorly palatine bone.
Above the floor – inferior rectus muscle, inferior oblique muscle.
Below the floor – maxillary sinus and palatine sinus.
Posterior part – infra orbital foramen [hole] – transmits, infra orbital
artery, infra orbital vein [connects to facial vein].

11. BASE OF THE ORBIT
•Orbital base is the anterior end of the orbit.
•It is bounded by orbital margins.
•The margins are formed by a ring of compact bone.
•It gives attachment to the septum orbit.
It is of four parts –
1. Superior orbital margin
2. Inferior orbital margin
3. Medial orbital margin
4. Lateral orbital margin

12. SUPERIOR ORBITAL MARGIN-
•It is formed by the frontal bone.
•Its lateral 2/3rd part is very sharp & medial 1/3rd is rounded.
•Above the frontal bone - supra orbital notch, bears supra orbital nerve &
artery.
•About 10mm medial to this notch - supra trochlear groove, transmits supra
trochlear nerve & artery.
INFERIOR ORBITAL MARGIN –
•It is formed by zygomatic bone laterally & maxilla medially.
•Medially, it becomes continuous with the anterior lacrimal crest.
•The infra orbital foramen transmitting their nerves & vessels, situated 4-5
mm below the orbital margin.

13. LATERAL ORBITAL MARGIN –
It is the more strong & formed by frontal bone & zygomatic bone.
The anterior half of the globe is not protected by these bone.
MEDIAL ORBITAL MARGIN –
It is formed by the anterior lacrimal crest of the maxilla & above by the
frontal bone.
Its upper part becomes continuous with the posterior lacrimal crest.

14. APEX OF THE ORBIT
Orbital apex is the posterior end of the orbit.
The apex has two orifices (opening)– optical canal & superior orbital
fissure [in sphenoid bone].
OPTICAL CANAL –
• It connects the orbit to the middle cranial fossa.
• It transmits the optic nerve & ophthalmic artery.
• Its normal dimensions, attained by the age of 4-5 years.
• Its average length is 6-11 mm.
• Tumours may lead to unilateral enlargement of optic canal, detected by X
ray.

16. SUPERIOR ORBITAL FISSURE –
• It is a comma shaped aperture in the orbital cavity, and attached by
sphenoid bone.
• It is situated lateral to the optic foramina at the orbital apex.
• The fissure(opening) is divided into upper, middle & lower parts by
common tendinous ring.
• The structures passing through the upper & lateral parts are the
lacrimal & frontal nerves, trochlear nerve, superior ophthalmic vein &
artery.
• The lower & medial parts of fissure - the inferior ophthalmic veins.
• The middle part of fissure transmits the oculomotor nerve, trigeminal
nerve & abducent nerve.

17. PERIORBITA
• The periosteum lining the surface of the orbital bones is called the
periorbita.
• It is loosely adhere with bone.
• It is firmly attached at the orbital margin, superior & inferior orbital
fissures, optic canal, lacrimal fossa & sutures.
• In optic canal, the optic nerve is closely attached to periorbita.
• At the orbital margin, periorbita is thicken & the orbital septum is attached.
• At the posterior lacrimal crest, the periorbita divides into two layers which
reunite at the anterior lacrimal crest.
• These two layers enclose the lacrimal sac.
• At the apex of orbit, the periorbita is thicken to form the common tendinous
ring.

19. ORBITAL FASCIA
•This part has head of fascia bulbi, muscular sheaths, inter-muscular
septum and extra ocular muscles ligaments.
• It is a thin connective tissue membrane lining the various intra orbital
structure.
•In the orbit, the surrounding fascia allows for smooth rotation and
protects the orbital contents. If excessive tissue accumulates behind
the ocular globe, the eye can protrude, or become exophthalmic.[4]
•Graves disease may also cause axial protrusion of the eye, known
as Graves' ophthalmopathy, due to build up of extracellular
matrix proteins and fibrosis in the rectus muscles. Development of
Graves' ophthalmopathy may be independent of thyroid function.[10]

21. FASCIA BULBI/TENON’S CAPSULE
•It covers the globe from the limbus to the optic disc.
•It is situated in close contact with sclera.
•The outer surface – posteriorly - orbital fat, anteriorly – subconjunctival
tissue (limbus).
•Fascia bulbi/ tenon’s capsule is pierced – posteriorly – optic nerve, ciliary
nerves and vessels and anteriorly by the - six extra ocular muscles.

22. SURGICAL SPACE IN THE ORBIT
These are most important as much orbital tumors tend to remain within the
space in which they are performed surgery by surgeon.
It has 4 spaces in the orbit –
1. Subperiosteal space
2. Peripheral orbital space (ant. space)
3. Central space
4. Sub-tenon’s space

23. ORBITAL FAT & RETICULAR TISSUE
•The orbital cavity is occupied by orbital fat, which extends from the optic
nerve to the orbital wall.
•It forms the apex of the orbit to the orbital septum.
•The fat lobules is situated in the interstices of a web of reticular tissue
called orbital reticulum.
•This tissue is the supporting framework of the orbital fat.
•Orbital fat is divided into central & peripheral parts by the intermuscular
septa.
•Posteriorly, where there is no intermuscular septum, the peripheral &
central fat parts are continuous with each other.
•The peripheral orbital fat consists of 4 lobules – superomedial,
superolateral, inferomedial & inferolateral.

24. APERTURES AT THE BASE OF ORBIT
The base of orbit is attached partially by the globe & EOM.
The 2 oblique muscles bound 5 orifices (aperture) b/w the orbital margin &
globe.
These apertures form a communication b/w the orbital cavity & eyelids.
Through it, blood & pus pass out of the orbit from the space b/w periorbita &
peripheral fat.
These aperture are –
1. Superior aperture
2. Superomedial aperture
3. Inferomedial aperture
4. Inferior aperture
5. Inferiolateral aperture

25. SUPERIOR APERTURE –
•This is a comma shaped orifice & situated b/w roof of the orbit &
upper surface of the LPS.
•The head of the comma is situated near the trochlea & the tail reaches
the lacrimal gland.
SUPEROMEDIAL APERTURE –
•It is vertically oval aperture is situated b/w the superior oblique
muscle & the medial ligament.
•The infra trochlear nerve, dorsal nasal artery & angular vein pass
through this aperture.

26. INFERO MEDIAL APERTURE –
•This is vertically oval in shape & is situated b/w the medial check
ligament, origin of inferior oblique & lacrimal sac.
INFERIOR APERTURE –
•This is triangular in shape & is bounded by the inferior oblique muscle,
arcuate expansion of inferior oblique & floor of the orbit.
INFERO LATERAL APERTURE –
•This is small oval aperture situated b/w the arcuate expansion of the
inferior oblique muscle and lateral check ligament.

27. CONTENTS OF THE ORBIT
• Eyeball occupies about 1/5th of the total orbital volume.
• Muscles includes - SR, IR, MR, LR, SO, IO, LPS & muller’s muscles.
• Nerves includes - optic nerve, oculomotor nerve, trochlear nerve,
abducent nerve, branches of ophthalmic nerve, branches of maxillary
division.
• Vessels includes - ophthalmic artery & its branches, infra orbital
vessels, meningeal artery, superior & inferior ophthalmic veins.
• Orbital fat, reticular tissue & orbital fascia.
• Lacrimal gland & lacrimal sac.

29. REFRENCES
• eye, human."Encyclopædia Britannica from Encyclopædia Britannica
2006 Ultimate Reference Suite DVD 2009.
• Moore, Keith L. (2010). Clinically Oriented Anatomy (6th ed.).
Lippincott Williams & Wilkins. ISBN 978-07817-7525-0.
• Hatton, M. P.; Rubin, P. A. (2002). "The pathophysiology of thyroid-
associated ophthalmopathy". Ophthalmol Clin North Am. 15 (1): 113–
119. doi:10.1016/S0896-1549(01)00004-9. PMID 12064074