Neuro Block 4: The Visual System and Upper Cranial Nerves

List 5 things the Eye socket/Orbital contains:

1. eyeball

2. optic nerve

3. extraocular muscles

4. lacrinal apparatus

5. nerves and vessels that innervate these structures

What is an important distinction between the axis of the orbit and the axis of the eyeball?

• the axis of the orbit is NOT aligned with the axis of the eyeball

Give the boundaries of the orbit:

• roof = frontal and sphenoid bone

• floor = palatine bone, maxillary bone, zygomatic bone

• medial wall = maxillary bone, lacrimal bone, ethmoid bone and sphenoid bone

• lateral wall = sphenoid and zygomatic bone

List the 6 layers of the eyelid:

1. skin

2. subcutaneous tissue

3. voluntary muscle = orbicularis oculi

4. orbital septum

5. tarsus

6. conjunctiva

What cranial nerve innervates the orbicularis oculi?

• facial nerve

Which ligaments attach to the medial and lateral sides of the orbit and what muscles follow the same path?

• medial and lateral palpebral ligaments

• tarsus muscles

What structures ensure foreign objects do not get ‘lost’ in the posterior part of the eyeball?

• superior and inferior fornix

List 4 Fissures/foramen of the orbital:

1. Superior Orbital Fissure

2. Inferior Orbital Fissure

3. Optic Canal

4. Nasolacrimal Canal

List the 4 cranial nerves that enter the orbit through the superior orbital fissure:

1. Ophthalmic branch of cranial nerve V (trigeminal)

2. Oculomotor CN III

3. Trochlear CN IV

4. Abducens CN VI

What nerve passes through the inferior orbital fissure?

• maxillary nerve

What nerve and what artery pass through the Optic canal?

1. Optic nerve CNII

2. Ophthalmic Artery

What passes through the Nasolacrimal canal?

• nasolacrimal duct (tear drainage)

What is the function of the Lacrimal Apparatus?

• the lacrimal apparatus produces tears (via lacrimal gland) and drains tears

List the drainage pathway of tears:

lacrimal gland produces tears → drain into lacrimal canaliculi → lacrimal sac → nasolacrimal duct → nasal cavity

List the extraocular muscles of the eye:

1. medial rectus

2. lateral rectus

3. superior rectus

4. inferior rectus

5. superior oblique

6. inferior oblique

7. levator palpebrae superioris

What muscle adducts the eye?

• medial rectus

What muscles abducts the eye?

• lateral rectus

What muscle elevates the eye?

• superior rectus

What muscle depresses the eye?

• inferior rectus

What muscle externally rotates the eye?

• inferior oblique

What muscle internally rotates the eye?

• superior oblique

What eye muscles does the oculomotor nerve innervate:

1. medial rectus

2. superior rectus

3. inferior rectus

4. inferior oblique

What nerve innervates the levator palebrae superioris?

oculomotor

What innervates the lateral rectus muscle?

• abducens nerve (CNVI)

What innervates the superior oblique muscle?

• trochlear nerve (CN IV)

When asking a patient to look up and right (without moving their head), what muscles are you testing?

• isolates movements for superior rectus (right eye) and inferior oblique (left eye)

When asking a patient to look right what muscles are you testing?

• Testing the lateral rectus for right eye

• Testing medial rectus for left eye

When asking a patient to look down and right what muscles are you isolating?

• This isolates the inferior rectus for right eye

• This isolates the superior oblique for the left eye

What artery supplies all structures in the orbit?

• ophthalmic artery (a branch of the internal carotid artery)

• enters through the optic canal (along with optic nerve)

List 2 veins of the orbit: What do they drain into?

1. Superior ophthalmic vein

2. Inferior ophthalmic vein 

→ both drain into cavernous sinus either side of pituitary gland

Summarise the optic nerve pathway:

arises in retina → exits orbit via optic canal → some fibres from this nerve form the optic chiasm → optic tract → synapse at thalamus → continue to visual cortex as optic radiation

Where specifically in the thalamus does the optic tract synapse?

• Lateral geniculate body

What is the function of the opti nerve?

• vision

• (special afferent innervation)

Where is the origin of the Oculomotor Nerve (CN III)?

• arises at midbrain

Summarise the pathway of the Oculomotor nerve:

oculomotor nerve arises at midbrain → exits the brain stem between midbrain + pons → passes through lateral wall of cavernous sinus → leaves cranial cavity through superior/radial fissure → enters orbit and divides into superior and inferior branches

Where does the trochlear nerve arise from?

• the midbrain at level of inferior colliculus

Where does the Abducens nerve arise from?

• the pons