4. APPLIED ANATOMY BONY ORBIT
The bony orbits are quadrangular truncated
pyramids situated between the anterior cranial
fossa above and the maxillary sinuses below Each
orbit is
about 40 mm in height, width and depth and is
formed by portions of seven bones : (1) frontal, (2)
maxilla,(3) zygomatic, (4) sphenoid, (5) palatine, (6)
ethmoid (7) lacrimal. It has four walls (medial,
lateral,
superior and inferior), base and an apex.
5. The medial walls of two orbits are parallel to
each other and, being thinnest, are frequently
fractured during injuries
The inferior orbital wall (floor) is triangular in
shape
and being quite thin is commonly involved in
blowout fractures and is easily invaded by tumours
of the
maxillary antrum.
6. The lateral wall of the orbit is triangular in shape.
covers only posterior half of the eyeball.
Therefore, palpation of the retrobulbar tumours is
easier from this side.
The roof is triangular in shape and is formed
mainly
by the orbital plate of frontal bone
Base of the orbit is the anterior open end of the
orbit. It is bounded by thick orbital margins.
7. The orbital apex - It is the posterior end of
orbit. Here the four orbital walls converge. It has
two orifices, the optic canal which transmits optic
nerve and ophthalmic artery and the superior
orbital fissure which transmits a number of
nerves, arteries and veins
ORBITAL FASCIA
It is a thin connective tissue membrane lining
various intraorbital structures. Though, it is one
continuous tissue.
8. It divided into fascia bulbi, muscular sheaths,
intermuscular septa, membranous expansions of
the extraocular muscles and ligament of
Lockwood.
Fascia bulbi (Tenon’s capsule) envelops the globe
from the margins of cornea to the optic nerve. Its
lower part is thickened to form a sling or
hammock on which the globe rests; this is called
‘suspensory ligament of Lockwood’.
9. CONTENTS OF THE ORBIT
The volume of each orbit is about 30 cc.
Approximately one-fifth of it is occupied by the
eyeball. Other contents of the orbit include: part
ofoptic nerve, extraocular muscles, lacrimal gland,
lacrimal sac, ophthalmic artery and its branches,
Third, Fourth and Sixth cranial nerves and
ophthalmic and maxillary divisions of the fifth
cranial nerve,
sympathetic nerve, orbital fat and fascia
10. SURGICAL SPACES IN THE ORBIT
These are of importance as most orbital
pathologies tend to remain in the space in which
they are formed.
Therefore, their knowledge helps the surgeon in
choosing the most direct surgical approach.
Each orbit is divisible into four surgical spaces
1. The subperiosteal space.
2. The peripheral space.
3. The central space.
4. Tenon’s space.
11.
12. PROPTOSIS
It is defined as forward displacement of the
eyeball beyond the orbital margins.
exophthalmos (out eye) is synonymous with it; but
somehow it has become customary to use the
term exophthalmos for the displacement
associated with thyroid disease.
CLASSIFICATION
Unilateral proptosis/Bilateral proptosis
Acute proptosis
Intermittent proptosis
Pulsating proptosis
13. Causes of unilateral proptosis include:
1. Congenital conditions. These include: dermoid
cyst, congenital cystic eyeball, and orbital
2. Traumatic lesions. These are: orbital haemorrhage,
retained intraorbital foreign body, traumatic
aneurysm and emphysema of the orbit.
3. Inflammatory lesions. Acute inflammations are
orbital cellulitis, abscess, thrombophlebitis,
panophthalmitis, and cavernous sinus thrombosis
(proptosis is initially unilateral but ultimately
becomes bilateral). Chronic inflammatory lesions
include: pseudotumours, tuberculoma, gumma and
sarcoidosis.
14. Causes of unilateral proptosis include
4. Circulatory disturbances and vascular lesions.
These are: angioneurotic oedema, orbital varix
and aneurysms.
5. Cysts of orbit. These include: haematic cyst,
implantation cyst and parasitic cyst (hydatid cyst
and cysticercus cellulosae).
6. Tumours of the orbit. These can be primary,
secondary or metastatic.
7. Mucoceles of paranasal sinuses, especially frontal
(most common), ethmoidal and maxillary sinus are
common causes of unilateral
15. Causes of bilateral proptosis include:
1. Developmental anomalies of the skull:
craniofacial dysostosis e.g., oxycephaly (tower
skull).
2. Osteopathies: Osteitis deformans, rickets and
acromegaly.
3. Inflammatory conditions: Mikulicz’s syndrome
and late stage of cavernous sinus thrombosis.
4. Endocrinal exophthalmos: It may be thyrotoxic
or thyrotropic.
5. Tumours: These include symmetrical lymphoma
or lymphosarcoma, secondaries from
neuroblastoma,
16. 6. Systemic diseases: Histiocytosis, systemic
amyloidosis, xanthomatosis and Wegener’s
granulomatosis.
C. Causes of acute proptosis. It develops with
extreme rapidity (sudden onset). Its common causes
are: orbital emphysema fracture of the medial
orbital
wall, orbital haemorrhage and rupture of ethmoidal
mucocele.
17. D. Cause of intermittent proptosis. This type of
proptosis appears and disappears of its own. Its
common causes are: orbital varix, periodic orbital
oedema, recurrent orbital haemorrhage and highly
vascular tumours.
E. Causes of pulsating proptosis. It is caused by
pulsating vascular lesions such as caroticocavernous
fistula and saccular aneurysm of
ophthalmic artery