Orbit Anatomy

Nasociliary nerve

Nasociliary nerve Introduction:

Nasociliary nerve is the branch of ophthalmic division of trigeminal nerve. It is sensory nerve to the Whole eyeball (eye, cornea, iris and ciliary body but not conjunctiva), Paranasal air sinus, mucous membrane of the nasal cavity, and Skin of the external nose.

1. Nasociliary nerve Course and relations

1. Runs through the tendinous ring between the two divisions of oculomotor nerve.
2. Passes by sitting on optic nerve I ON optic nerve)! and below superior rectus.
3. Enters anterior ethmoidal foramen as anterior ethmoidal nerve.
4. Runs in the roof of middle and anterior ethmoidal air cells.

Read And Learn More: Face Anatomy Notes And Important Questions

2. Nasociliary nerve Branches of nasociliary nerve

1. Communicating branches to ciliary ganglion: It forms sensory root to ciliary ganglion.

2. Nasociliary nerve Collateral branches

Long ciliary nerve:

Long ciliary nerve  is sensory to

1. Cornea,
2. Iris, and
3. Ciliary body.

Long ciliary nerve is sympathetic to dilator pupillae.

1. Posterior ethmoidal nerve: It is sensory to following air sinuses
2. Posterior ethmoidal sinus, and Sphenoidal air sinus.

3. Nasociliary nerve Terminal branches
Infratrochlear nerve (smaller terminal branch): It is sensory to

1. Conjunctiva,
2. Lacrimal sac,
3. Caruncle,Medial end of eyelids, and
4. Upper half of the external nose.

Anterior ethmoidal nerve (larger terminal branch): It is sensory to

1. Anterior ethmoidal sinus,
2. Middle ethmoidal sinus.
3. Dura mater of anterior cranial fossa
4. Mucosa of nose, and
5. Skin of the lower half of the nose.

3. Nasociliary nerve  Applied anatomy: A lesion of the nasociliary nerve at the superior orbital fissure causes Paraesthesia in the forehead and nose, and Loss of corneal blink reflex.

Short Ciliary Nerves

1.Short Ciliary Nerves Origin: Arise from ciliary ganglion. They are 15 to 20 in number.
2. Short Ciliary Nerves Course: They pass with the optic nerve to the back of the eyeball.
3. Short Ciliary Nerves Distribution: They supply

1. Ciliary body (oculomotor nerve fibres), which is concerned with accommodation.
2. Circular muscle of iris (oculomotor nerve fibres), which constricts the pupil.
3. Radial fibres of iris (sympathetic nerve fibres), which dilate the pupil.

Question1:  What is squint (strabismus)?
Answer 1. squint is weakness or paralysis of muscles of eyeball.
2. squint may be concomitant or paralytic.

1. Concomitant squint is congenital.
   Movements are not affected and there is no diplopia.
2. In paralytic squint, movements are limited.
   There is diplopia and vertigo.
   The head is turned in the direction of the function of paralysed muscle.
   There is a false orientation of the field of vision.

What is Tenon’s capsule?

1. Tenon’s capsule Definition:

Tenon’s capsule forms a thin, loose membranous sheath around the eyeball.

2. Tenon’s capsule Extent:

Tenon’s capsule extends from the optic nerve to the sclerocorneal junction.

3. Tenon’s capsule  Function:

Free movement of eyeball within the sheath.

4. Tenon’s capsule  Structures piercing

1. Tendons of the various extraocular muscles.
2. Ciliary vessels.
3. Ciliary nerves.

5. Tenon’s capsule  Expansions

1. A tubular sheath covers each orbital muscle.
2. The medial check ligament is a strong.lar expansion of medial rectus muscle.
3. Tenon’s capsule is attached to the lacrimal bone.
4. The lateral check ligament is a stronglar expansion from the sheath of the lateral rectus muscle.
   ITenon’s capsule is attached to zygomatic bone.
5. The lower part of Tenon’s capsule is thickened and is named the suspensory ligament of the eye or the suspensory ligament of Lockwood.
   Tenon’s capsule is expanded in the centre and narrows at its extremities and is slung like a hammock below the eyeball.
6. Tenon’s capsule is formed by union of margins of sheaths of Inferior rectus and Inferior oblique muscles with Medial and lateral check ligaments.

Question 2: What is the mode of blood supply of optic nerve?
optic nerve is divided into arterial supply and venous return.

1. Optic Nerve Arterial supply:

The arteries form plexus. They are derived from two sources

Plexus formed by the

1. Superior hypophyseal artery, branch of internal carotid artery,
2. Ophthalmic artery,
3. Posterior ciliary artery (branch of ophthalmic artery), and Extraneural branches of central artery. Branches of the central artery.

2. Venous return: Central vein.

Palpebral (canthal) ligaments

These ligaments connect the tarsal plates to the orbits. They are medial and lateral palpebral ligaments.

Medial palpebral ligament

1. Medial Palpebral Ligament is well-developed.
2. Medial Palpebral Ligament is superficially situated.
3. Medial Palpebral Ligament conncts medial ends of two tarsal plates to the anterior lacrimal crest and frontal process of maxilla.
4. At its insertion, it splits into tarsal plates to surround lacrimal canaliculi. It lies in front of nasolacrimal sac and the orbital septum.

Lateral palpebral ligament

1. Lateral Palpebral Ligament is poorly developed.
2. Lateral Palpebral Ligament extends from the lateral ends of tarsal plates to small tubercle on the zygomatic bone (Whitnall’s tubercle).
3. Lateral Palpebral Ligament is deeply situated.
4. Lateral Palpebral Ligament lies deep to orbital septum and lateral palpebral raphe of orbicularis oculi.

Question4 : Why the paralysis of extraocular muscles causes diplopia?

1. The perception of two images of a single object is called diplopia.

2. The objects lying in different parts of the visual field produce images over different spots on the retina.

3. The brain judges the position of an object by the position at which its image is formed on the retina.

4. Normally, the movements of the right and left eyes are in perfect alignment, and an object casts an image on corresponding spots on the two retinae so that only one image is perceived by the brain.

5. When a muscle of the eyeball is weak, and a movement involving that muscle is performed, the movement of the defective eye is slightly less than that of the normal eye.

6. As a result, images of the object on the two retinae are not formed at corresponding points but over two points near each other.

The brain, therefore, ‘sees’ two images,one from each retina.

Question5 : What is conjugate movements of eyes?
Normally, movements of the two eyes are harmoniously coordinated.
Such coordinated movements of both eyes are called conjugate ocular movements.

Question6 : What is nystagmus?
Answer: 1. An involuntary rhythmical, oscillatory movement of eyeball is called nystagmus.
2. This is due to incoordination of the ocular muscles. It may be either

1. Vestibular or
2. Cerebellar, or even
3. Congenital.

Orbital nerve

It is a branch of pterygopalatine ganglion. It is actually branch of maxillary nerve. It also carries parasympathetic and sympathetic fibres which pass through the ganglion.

1. Course: It passes through the inferior orbital fissure.
2. Distribution: It supplies the

1. Periosteum of the orbit, and
2. Orbitalis muscle.
3. Mucous membrane of sphenoidal and ethmoidal air sinuses.