Orbits & its contents

 Features

• The orbits are pyramidal cavities, 
• situated one on each side of the root of the nose. 
• They provide sockets for rotatory movements of the eyeball. 
• The long axis of the each orbit passes backwards and medially. 
• The medial walls are parallel to each other at a distance of 2.5 cm
• but the lateral walls are set at right angles to each other.

Contents

1. Eyeball: Eyeball occupies anterior one-third of orbit.

2. Fascia: Orbital and bulbar.

3. Muscles: Extraocular and intraocular.

4. Vessels: Ophthalmic artery, superior and inferior ophthalmic veins, and lymphatics.

5. Nerves: Optic, oculomotor, trochlear and abducent; branches of ophthalmic and maxillary nerves, and sympathetic nerves.

6. Lacrimal gland: 

7. Orbital fat.

Visual Axis ond Orbital Axis

Axis passing through centres of anterior and posterior poles of the eyeball is known as visual axis. 

It makes an angle of 20 - 25˚ with the orbital axis, (line passing through optic canal and centre of base of orbit,)

Orbital Fascia or Periorbita

• It forms the periosteum of the bony orbit. 
• Due to the loose connection to bone, it can be easily stripped.
• Posteriorly, it is continuous with the dura mater and with the sheath of the optic nerve. 
• Anteriorly, it is continuous with the periosteum lining the bones around the orbital margin.
• There is a gap in the periorbita over the inferior orbital fissure. 
• This gap is bridged by connective tissue with some smooth muscle fibres in it. 
• These fibres constitute the orbitalis muscle.
• a. At the upper and lower margins of the orbit, the orbital fascia sends off flap-like continuations into the eyelids. These extensions form the orbital septum.
• b. A process of the fascia holds the fibrous pulley of the tendon of the superior oblique muscle in place.
• c. Another process forms the lacrimal fascia which bridges the lacrimal groove.

Fascial Sheath of Eyeball of Bulbar Fascia

1. Tenon's capsule forms a thin, loose membranous sheath around the eyeball, extending from the optic nerve to the sclerocorneal junction or limbus. 

It is separated from the sclera by the episcleral space which is traversed by delicate fibrous bands. 

The eyeball can freely move within this sheath.

2. The sheath is pierced by:

a. Tendons of the various extraocular muscles.

b. Ciliary vessels and nerves around the entrance of the optic nerve.

3. The sheath gives off a number of expansions.

a. A tubular sheath covers each orbital muscle.

b. The medial check ligament is a strong triangular expansion from the sheath of the medial rectus muscle; it is attached to the lacrimal bone.

c. The lateral check ligament is a strong triangular expansion from the sheath of the lateral rectus muscle; it is attached to the zygomatic bone

4. The lower part of Tenon's capsule is thickened, and is named the suspensory ligament of the eye or the

suspensory ligament of Lockwood .

It is expanded in the centre and narrow at its extremities, and is slung like a hammock below the eyeball. 

It is formed by union-of the margins of the sheaths of the inferior rectus and the inferior oblique muscles with the medial and lateral check ligaments.

Watch lectures on YouTube:

Orbit | Boundaries | Fissures and Foramina | Relations | Contents