anatomy of orbit

1. ANATOMY OF ORBIT

2. REFERENCES
1. A K Khurana & Indu Khurana – Anatomy and
physiology of eye.
2. Parsons diseases of the EYE - by Ramanjit
sihota and Radhika tandon.
3. Comprehensive Ophthalmology by A K
Khurana.

3. > Bony orbit is formed from the
mesenchyme surrounding the
optic vesicle beginning at 06
weeks of embryonic age.

4. FORMED BY SEVEN BONES
• 1. Frontal
• 2. Ethamoid
• 3. Lacrimal
• 4. Palatine
• 5. Maxilla
• 6. Zygomatic
• 7. Sphenoid

5. SHAPE
• The two bony orbits are quadrangular truncated
pyramids b/w anterior cranial fossa above and
maxillary sinuses below.
• The medial walls of two orbits are parallel to each
other.
• Lateral wall of each orbit lies at an angle
> 45 ’ with medial wall
> 90 ‘ with lateral wall of other orbit.

6. DIMENSIONS
• Depth – 42 mm along medial wall
50 mm along lateral wall.
. Base – 40 mm in width
35 mm in height.
. Inraorbital width – 25mm(medial margins)
. Extraorbital width – 100mm(lateral margins)

7. MEDIAL WALL
• Quadrilateral in shape.
• Formed by, from front to back-
1. frontal process of maxilla
2. the lacrimal bone
3. orbital plate of the ethamoid
4. body of sphenoid

8. Cont…
• The anterior part of medial wall bears the lacrimal
sac fossa. Medial to lacrimal fossa lie the anterior
ethamoidal sinus(upper part) and middle meatus of
nose(lower part).
• Attachments – posteriorly are
1. Horner’s muscle(lacrimal fibres of orbicularis)
2. Septum orbitale
3. Check ligament of the medial rectus muscle

9. RELATIONS
• Medial to the medial wall lie anterior ethamoidal
sinuses, middle meatus of nose, middle and
posterior ethamoidal sinuses and sphenoidal sinus.
• Orbital surface of medial wall is related to superior
oblique muscle in the upper part near the roof and
medial rectus muscle in the middle part. In
between these two muscles- anterior and
posterior ethamoidal nerve, infratrochlear nerve
and terminal branch of ophthalmic artery.

11. CLINICAL APPLICATIONS
• Medial wall is the thinnest wall of orbit(0.2-0.4 mm)
and also called as lamina papyracea.
• Ethamoiditis being the commonest cause of orbital
cellulitis.
• Medila wall is frequently eroded by inflammatory
lesions, cysts and neoplasms that originate from
adjacent air sinuses.
• Easily fractured during injuries as well as orbitotomy
operations.
• During surgery along this wall, heamorrhage is most
troublesome due to injury to ethamoidal vessels.
• The medial wall can be easily visualised with routine
PA radiographs of orbit.

12. INFERIOR WALL (FLOOR)
• Triangular in shape, shortest of all walls and
extending about 35 to 40 mm from inf margin.
• Formed by 3 bones-
1. Maxillary bone medially
2. Zygomatic bone laterally and
3. Palatine bone posteriorly.
. It slopes downwards from posterior to anterior by
~ 20’.
. Posterior part of floor is separated from lateral
wall by inferior orbital fissure.

13. RELATIONS
• Below it is related to maxillary sinus and
palatine air cells.
• Above it is related to inferior rectus muscle,
inferior oblique muscle and nerve to inferior
oblique.
• Inferior oblique muscle originates just lateral
to opening of nasolacrimal duct.

15. CLINICAL APPLICATIONS
• Orbital floor being thin is commonly involved
in ‘ blow-out fractures’ and also is easily
invaded by tumors of maxillary antrum.
• Floor is best visualised with standard
posteroanterior radiographs.

16. LATERAL WALL
• It is thickest , strongest, triangular in shape.
• It is formed by –
1. Zygomatic bone anteriorly
2. Greater wing of sphenoid bone posteriorly.
. On the posterior part of lateral wall – a bony projection –
spina recti lateralis.
. On anterior part – a bony projection – lateral orbital
tubercle of Whitnall.( att to check ligament of lateral
rectus muscle, and to suspensary ligament of eyeball,
lateral palpebral ligament and aponeurosis of levator
muscle.
. Posteriorly lateral wall is separated from the roof by
superior orbital fissure and from the floor by the inferior
orbital fissure.

17. RELATIONS
• Laterally , the lateral wall separates the orbit
from temporal fossa anteriorly and from the
middle cranial fossa posteriorly.
• Medially it is related to lateral rectus, lacrimal
nerve and vessels and zygomatic nerve.

19. CLINICAL APPLICATIONS
• Lateral wall covers only posterior half of
eyeball. Anterior half is not covered by bone.
Hence ,palpation of retrobulbar tumors is easier
from lateral.
• Lateral orbital surgical approach is common.
• No foramina in lateral wall, so anterior part can
be breached without serious haemorrhgae.

20. ROOF (VAULT)
• Triangular in shape and formed by mainly
orbital plate of frontal bone and posteriorly by
the lesser wing of sphenoid bone at apex.
• Anterolateral part has a depression – fossa for
the lacrimal gland.
• Roof slopes backwards and downwards towards
apex.
• Trochlear fossa- small depression at the junction
of roof and medial wall- for the pulley of
superior oblique.

21. RELATIONS
• Above its related to frontal lobe of cerebrum,
meninges and frontal sinuses.
• Below are periorbita, frontal nerve, levator
palpebrae superioris, superior rectus, superior
oblique, trochlear nerve and lacrimal gland.
• At junction of roof and lateral wall is a gap
posteriorly- superior orbital fissure.

23. CLINICAL APPLICATIONS
> Roof is thin throughout its extent and the
periorbita easily peels away from its
undersurface
> On the cranial side , the dura can be easily
lifted, because the roof is not perforated by
nerves or vessels
> Sharp objects injury to roof can penetrate
and damage the frontal lobe.

24. SCHEMATIC VIEW OF ORBITAL CAVITY

25. BASE OF ORBIT
• Anterior open end of orbit is base, bounded by
orbital margins.
• Margins are formed by a ring of compact bone,
gives attachment to the septum orbitale.
> Superior orbital margin – formed by orbital arch
of the frontal bone – lateral 2/3 is sharp and
medial 1/3 is rounded – at the junction is
supraorbital notch, which transmits supraorbital
nerve and artery.
10 mm medial to notch is supratrochlear groove
which transmits supratrochlear nerve and artery.

26. Cont….
> Lateral margin – its strongest , formed by
zygomatic process of frontal bone and zygomatic
bone. It is deficient anteriorly.
> Inferior orbital margin - formed by zygomatic
bone laterally and maxilla medially. 4-5mm
below margin is infraorbital foramen which
transmits infraorbital nerve and vessels.
> Medial orbital margin - formed by ant lacrimal
crest on frontal process of maxilla below and
frontal bone above. Its upper part becomes
continuous with the posterior lacrimal crest.

27. APEX OF ORBIT
• It is the posterior end of orbit. Where 4 walls
converge
• Apex has two orifices optic canal and sup
orbital fissure situated in sphenoid bone.
• At the apex jus below optic canal inf orbital
fissure joins the sup orbital fissure and is
contiguous with foramen rotundum .

28. OPTIC CANAL
• It connects orbit to middle cranial fossa.
• Transmits optic nerve and ophthalmic artery.
• Normal adult dimensions are attained by the age
of 4-5 years.
• Average length is 6-11mm.
• Orbital end is vertically oval, cranial end is
horizontally oval, and center is circular.
• Tumors like optic nerve glioma and meningiomas
may lead to enlargement of optic canal(detected
on X-ray films.

29. SUPERIOR ORBITAL FISSURE
• Comma shaped aperture in orbital cavity, bounded
by lesser and greater wing of sphenoid bone. It is
situated lateral to optic foramen.
• Fissure is divided into upper, middle and lower parts
by common tendinous ring(for origin of recti).
• Structures passing through - are
1. Lacrimal, frontal and trochlear nerve.
2. Sup ophthalmic vein and recurrent branch of
ophthalmic artery.
3. Sup and inf divisions of 3rd C N, nasociliary branch
of ophthalmic division of 5th and 6th C N.
4. Inf ophthalmic vein.

30. INFERIOR ORBITAL FISSURE
• Inf orbital fissure lies just below the sup orbital
fissure b/w lateral wall and floor of orbit, giving
access to the pterygopalatine and
inferotemporal fossae.
• Structures passing through – are
1. Infraorbital and zygomatic branches of the
maxillary div of 5th C N.
2. Orbital branch of pterygopalatine ganglion.
3. Branch of inf ophthalmic vein(communicates
with pterygoid plexus).

31. PERIORBITA
• It is the periosteum lining the orbital surface of
the bones of orbit.
• In the optic canal , the dural sheath of optic nerve
is closely adherent to periorbita.
• At the orbital margin , periorbia is thickened to
form the arcus marginale to which the septum
orbitale is attached.
• At the post lacrimal crest , periorbita splits into
two layers and encloses lacrimal sac and reunite
at ant lacrimal crest.
• At the apex the periorbita is thickened to form
the common tendinous ring of zinn.

32. FASCIA BULBI
• Fascia bulbi or tenon’s capsule is a dense,
ealastic, and vascular connective tissue that
envelops the globe from the limbus to the optic
disc.
• The lower part of fascia bulbi is thickened and
take part in the formation of a sling or hammock
on which the globe rests( suspensary ligament of
lockwood).
• Around the distal end of the optic nerve. The
fascia is fused with the dural sheath of the optic
nerve.

33. SURGICAL SPACES IN THE ORBIT

34. 1. SUBPERIOSTEAL SPACE
It is a potential space b/w orbital bones and
periorbita. Dermoid cyst, epidermoid cyst,
mucocele, subperiosteal abscess, myeloma,
osteomatous tumors, haematoma and fibrous
dysplasia are commonly seen in this space.
Plain X-ray are most useful in diagnosing the
tumors of this space.

35. 2. PERIPHERAL ORBITAL SPACE
• It is bounded peripherally by periorbita, internally
by four extraocular muscles with their
intermuscular septa and anteriorly bythe septum
orbitale.
• Tumors in this space produce eccentric proptosis
and can usually be palpated.
• Common tumors are – malignant lympoma,
capillary haemangioma of childhood, intrensic
neoplasms, of lacrimal gland and pseudotumors.

36. 3. CENTRAL SPACE
• Also called muscular cone or retrobulbar space.
• Bounded anteriorly by tenon’s capsule and peripherally
by recti muscles and their intermuscular septa.
• Contents – optic nerve and its meninges, divisions of 3rd
C N, 6th CN, nasociliary nerve, ciliary ganglion,
ophthalmic artery and sup ophthalmic vein.
• Tumors of this space includes - cavernous
haemangioma of adults, solitary neurofibroma,
neurilemomas, nodular orbital haemangiomas and optic
nerve gliomas . And usually produce axial proptosis.

37. 4. SUB-TENON’S SPACE
• It is a potential space around the eyeball b/w
the sclera and tenon’s capsule.
• Pus collected in this space is drained by
incision of tenon’s capsule through the
conjunctiva.

38. APERTURES AT THE BASE OF ORBIT
• The base of orbit is partially closed by the
globe and extraocular muscles with their facial
expansions . These expansions and two
oblique muscles bound about 5 orifices b/w
orbital margin and globe.
• Through these orifices fat may herniate from
orbit to come into contact with septum
orbitale.

39. • 1. Superior aperture
• 2. Superomedial aperture
• 3. Inferomedial aperture
• 4. Inferior aperture
• 5. Inferolateral aperture.

40. THANK YOU