Bony Orbit

• Orbit: Bony orbit; orbital cavity; space of compartment of the head which is bound by the internal surface of the wall of orbit.
• Orbit contains the eye, anterior portion of the optic nerve, ocular muscles and ocular adnexa.
• The medial ends of the posterior surfaces of both horizontal plates together form a bony projection in the midline, called the median posterior nasal spine.
• Posterior border of the pharynx faces the posterior wall of the pharynx.
• Median posterior nasal spine serves as an attachment site for the uvular muscle.
• Orbit is placed on the either side of the midsagittal plane of the skull between the cranium and the skeleton of the face.
• Orbit is shaped like a four sides pyramid with the base at the anterior orbital margin and the apex at the posterior margin (at the optic foramen).
• Orbit is designed to support and provide protection to the orbital soft tissues.
• Orbit is intended essentially as a socket for the eyeball, containing the muscles, orbital fats, nerves, vessels proper to it.
• Orbit also transmits certain vessels and nerves to supply the areas of the orbital aperture.
• The widest part of the orbit is 1.5 mm behind the orbital margin.
• The seven bones from which the orbit is constructed have complex shapes that together look like pieces of a three dimensional jigsaw puzzle to form the roughly pyramidal geometry of the orbit.
• The bones of the orbit are not perfect because various gaps and holes through which blood vessels are nerves enter and exit the orbital cavity.
• The Frontal bone has two surfaces: the orbital surface, which faces towards the contents of the orbit, and the nasal surface, which is concave and faces towards the nose.
• The Maxillary bone forms the medial orbital margin, formed by the anterior lacrimal crest on the frontal process of the maxilla and the posterior lacrimal crest on the lacrimal.
• The Frontal bone also forms the lateral orbital margin, the thickest among the margins but it is also the most exposed to injury.
• The Frontal bone forms the superior orbital margin, an easily palpable prominence, sharp in its lateral two thirds, located 25 mm from the midline and more rounded medially.
• The Zygomatic bone forms the inferior orbital margin, raised slightly above the floor or the orbit.
• The orbital margin is the most common quadrilateral with round corners, made up of three bones: Frontal, Zygomatic, and Maxillary.
• The Lacrimal bone has one surface: the orbital surface, which faces towards the contents of the orbit.
• The Lacrimal bone, the smallest bone of the skull and the most fragile bone of the face, makes up the most anterior part of the medial wall of the orbit and supports parts of the lacrimal apparatus (lacrimal sac and lacrimal canaliculi).
• Orbit is bounded by the anterior cranial fossa superiorly, nasal cavity and air sinuses, medially, inferiorly it is bounded by the antrum of Highmore (maxillary sinus), and the middle cranial and temporal fossa laterally.
• Depth of the Orbit: 40 mm.
• Height of the Orbital Opening: 35 mm.
• Width of the Orbital Opening: 40 mm.
• Interorbital Distance: 25 mm.
• Volume: 30 mm.
• Volume Ratio of the Orbit to the Eye: 5.5 : 1.
• Eyeball: Spheroidal structure containing sense receptors for vision, houses the retina- an extremely active layer of nerve tissue made up of millions of light receptors (photoreceptors).
• Orbital Fats & Fascia: Lies posterior to the orbital septum and anterior to the levator aponeurosis (upper lid) or the capsulopalpebral fascia (lower lid).
• Blood vessels of the eye consist of ophthalmic artery and a central retinal artery (an artery that branches off of the ophthalmic artery) provide blood to each eye.
• Long and Short Ciliary Nerves provide sensory innervation to the eyeball, including the cornea.
• Lacrimal Glands are paired, almond-shaped exocrine glands, one for each eye, that secrete the aqueous layer of the tear film.
• Optic Nerve, also known as the second cranial nerve(CN II), is a paired cranial nerve that transmits visual information from the retina to the brain.
• Extra Ocular Muscle (EOM) is responsible for controlling the movements of the eyeball and upper eyelid, also known as the “Extrinsic eye muscles”.
• The posterior portion of the lacrimal bone, posterior to the posterior lacrimal crest, is a smooth surface that participates in forming the medial wall of the orbit which is also the place of origin of the orbicularis oculi muscle.
• The palatine bone is a paired bone located between the maxillae and the pterygoid process of the sphenoid bone.
• The palatine bone is composed of two plates: horizontal plate and perpendicular plate.
• The descending process of the lacrimal bone, anteriorly and extending downward, articulates with the lacrimal process of the inferior nasal concha and participates in enclosing the bony canal for the nasolacrimal duct.
• The inferior part of the lacrimal fossa contains the nasolacrimal duct.