In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. “Orbit” can refer to the bony socket or it can also be used to imply the contents. The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and nasolacrimal duct, the eyelids, medial and lateral palpebral ligaments, check ligaments, the suspensory ligament,septum, ciliary ganglion and short ciliary nerves. In addition to the eyeball itself, the orbit contains the muscles that move the eye, blood vessels, and nerves. The orbit also contains the lacrimal gland that is located underneath the outer portion of the upper eyelid. The lacrimal gland produces tears that help lubricate and moisten the eye, as well as flush away any foreign matter that may enter the eye. The tears drain away from the eye through the nasolacrimal duct, which is located at the inner corner of the eye.
Borders and Anatomical Relations
The orbit can be thought of as a pyramidal structure, with the apex pointing posteriorly and the base situated anteriorly. The boundaries of the orbit are formed by seven bones.
It is also important to consider the anatomical relations of the orbital cavity – this is clinically relevant in the spread of infection, and in cases of trauma.
The borders and anatomical relations of the bony orbit are as follows:
a) Roof (superior wall) – Formed by the frontal bone and the lesser wing of the sphenoid. The frontal bone separates the orbit from the anterior cranial fossa.
b) Floor (inferior wall) – Formed by the maxilla, palatine and zygomatic bones. The maxilla separates the orbit from the underlying maxillary sinus.
c) Medial wall – Formed by the ethmoid, maxilla, lacrimal and sphenoid bones. The ethmoid bone separates the orbit from the ethmoid sinus.
d) Lateral wall – Formed by the zygomatic bone and greater wing of the sphenoid.
e) Apex – Located at the opening to the optic canal, the optic foramen.
f) Base – Opens out into the face, and is bounded by the eyelids. It is also known as the orbital rim.
Orbital fissures & Optic Canal
The major nerves and vessels to the orbit and globe enter through 3 openings. The superior orbital fissure is bounded by the lesser and greater wings of the sphenoid. The greater wing of the sphenoid, the maxilla, and the palatine bones of the orbit form the boundaries of the inferior orbital fissure. The optic canal is at the apex of the orbit and lies within the sphenoid bone. The structures entering through the optic canal are as follows:-
a) Optic nerve
b) Ophthalmic artery
c) Central retinal vein
The bony orbit contains the eyeballs and their associated structures:-
a) Extra-ocular muscles – These muscles are separate from the eye. They are responsible for the movement of the eyeball and superior eyelid.
b) Eyelids – These cover the orbits anteriorly.
c) Nerves: Several cranial nerves supply the eye and its structures; optic, oculomotor, trochlear, trigeminal and abducens nerves.
d) Blood vessels: The eye receives blood primarily from the ophthalmic artery. Venous drainage is via the superior and inferior ophthalmic veins.
Oculoplasty is the art and science of plastic surgery around the eye. The eyeball is a delicate structure, protected from harm by eyelids in front and the bony cup (socket) behind. Behind the eyeball run the nerves , arteries and muscles, which carry messages to the brain, move the eyeball, and provide nutrition to the eye. Oculoplasty deals with all these structures surrounding the eyeball. Oculoplastic surgeons first train as ophthalmologists, when they learn in details about the eye. During further higher training, they start to handle plastic surgery. They have the best knowledge about the eye and its surrounding; as eye surgeons, they are also ready to handle the most delicate of structures. This combination of skills makes the oculoplastic surgeons the best to do plastic surgery around the eye.
a) Blepharoplasty (eyelift) is plastic surgery of the eyelids to remove excessive skin or subcutaneous fat
b) Asian blepharoplasty
c) Ptosis repair for droopy eyelid.
d) Ectropion repair
e) Entropion repair
f) Canthal resection
g) A Canthectomy is the surgical removal of tissue at the junction of the upper and lower eyelids
h) Cantholysis is the surgical division of the canthus
i) A Canthoplasty is plastic surgery at the canthus
j) A Canthorrhaphy is suturing of the outer canthus to shorten the palpebral fissure
k) A Canthotomy is the surgical division of the canthus, usually the outer canthus
l) A Lateral Canthotomy is the surgical division of the outer canthus.
m) Tarsorrhaphy is a procedure in which the eyelids are partially sewn together to narrow the opening (i.e. palpebral fissure).
Surgery involving the lacrimal apparatus
a) DCR (Dacryocystorhinostomy) for Tearing
b) Canaliculodacryocystostomy is a surgical correction for a congenitally blocked tear duct in which the closed segment is excised and the open end is joined to the lacrimal sac
c) Canaliculotomy involves slitting of the lacrimal punctum and canaliculus for the relief of epiphora
d) A Dacryoadenectomy is the surgical removal of a lacrimal gland
e) A Dacryocystectomy is the surgical removal of a part of the lacrimal sac
f) A Dacryocystorhinostomy (DCR) or dacryocystorhinotomy is a procedure to restore the flow of tears into the nose from the lacrimal sac when the nasolacrimal duct does not function