The Orbit and Associated Structures

Question 1

What are the orbital and optical axis?

Answer 1

The orbital axis is the axis in which the eyes and optic nerve follow coming from the brain, it forms a triangle shape coming outwards from inside the head

The optical axis are the direction in which the eyes actually face, they are parallel and face forward

Question 2

What are the bones of the orbit?

Answer 2

Roof - frontal and sphenoid

Floor - maxilla, zygomatic (and palatine)

Medial - ethmoid, maxilla and lacrimal bones

Lateral - zygomatic and sphenoid

Question 3

What are the orbital fissures and fossae? And their associated contents?

Answer 3

Optic canal - optic nerve

Superior orbital fissure - lateral to medial:

• Lacrimal nerve
• Trochlear nerve
• Frontal nerve
• Oculomotor nerve
• Abducent nerve
• Superior ophthalmic vein

Inferior orbital fissure - infraorbital nerve

Etc… more fissures and nerves

Question 4

Describe the optic nerve.

Answer 4

CN II
1.2m axons from retinal cells
Coverings of pia (delicate), arachnoid (web-like) and dura (tough) maters (mother) of meninges, continuous with the brain (infection spread route)
Central artery and vein
If there is raised ICP, then it can lead to venous engorgement, and then can lead to papilloedema

Question 5

What is the optic chiasma?

Answer 5

A place where some nerves cross over and some stay on the same side

Question 6

Where do fractures of the orbit usually occur?

Answer 6

Normally a blow-out fracture

Medial and inferior walls are the thinnest and so the ones normally fractured

The medial wall can involve the ethmoidal and sphenoidal sinus
The inferior wall can involve maxillary sinus

The dangers are infections from the sinuses and infraorbital bleeding

Question 7

What are the muscles of eye movement?

Answer 7

4 recti (straight) muscles:

• Superior rectus muscle (pulls eye up)
• Inferior rectus muscle (pulls eye down)
• Lateral rectus muscle (pulls eye laterally)
• Medial rectus muscle (pulls eye medially)

2 obliques (slanted) muscles:

• Superior oblique muscle (intorsion) (down and in)
• Inferior oblique muscle (extorsion) (up and out)

Controlled by three cranial nerves

Question 8

What are the nerves of the muscles of the eye movements?

Answer 8

Lateral rectus muscle - CN VI Abducent
Superior oblique muscle - CN IV Trochlear
The rest are CN III Oculomotor

Question 9

What is the main arterial supply of the orbit?

And where does it come from?

Answer 9

Ophthalmic artery
Branch of the internal carotid, via optic canal
Any blockage leads to immediate blindness

Question 10

Which artery supplies the internal surfaces of the eye and where does it arrive from?

Answer 10

Central artery of retina

Arises from the ophthalmic artery

Question 11

What are the main branches of the ophthalmic artery?

Answer 11

Central retinal artery
Lacrimal artery - lacrimal glands, eyelids, conjunctiva
Posterior ciliary arteries - posterior external eye
Muscular branches to extraocular muscles
Other spate branches to ethmoidal and frontal sinuses, eyelids, forehead and scalp etc….

Question 12

Describe the venous drainage of the orbit?

Answer 12

Superior ophthalmic vein
- From inner angle to orbit to SOF

Inferior ophthalmic vein
- From plexus on floor and medial wall to then drain
either by SOF or IOF

Question 13

What is the danger triangle?

Answer 13

IT is an area of the face over the nose where the facial veins communicate to the cavernous sinus via ophthalmic veins
This means infection can spread easily from the face to the brain

Question 14

What is the function of the eyelids?

Answer 14

Protect from light and injury

Prevent corneal drying, through controlled spread of lacrimal fluid (tears)

Question 15

What are the two angles between the eyelids called? and what is the space between the eyelids called?

Answer 15

Lateral and medial canthus

Palpebral fissure

Question 16

What is it called when there is a drooping of one eyelid?

Answer 16

A ptosis

Question 17

What are the muscles of the eyelids?

Answer 17

Opening:

• Levator palpebrae superioris muscle. (CN III)
• Superior tarsal muscle

Closing:
- Orbicularis oculi (CN VII)

Question 18

Describe the anatomy of the eyelid, from anterior to posterior

Answer 18

Skin
Areolar tissue
Fibres of orbicularis oculi (circular muscles around eye)
Levator palpebrae superioris
Superior tarsus
- dense connective tissue strengthening “skeleton”
- (Inferior tarsus in lower lid)
Tarsal (meibomian) glands, secrete oil (to keep fluid in eye and keep it moist) (if they aren’t working then get dry eyes)
Ciliary glands (sebaceous) (inflamed - stye)
Palpebral conjunctiva.

Question 19

Describe the bilateral blinking reflex

Answer 19

It protects eye and keeps them moist
Triggers:
   - Corneal drying
   - Corneal irritation or contact (perceived as pain)
   - Expectation of contact

Corneal blink reflex is via the CN V1 - sensory and CN VII)

Question 20

What happens if you get paralysis of Orbicularis oculi?

Answer 20

Innervated by CN VII - facial nerve

Failure to close eyes, e.g. Bells Palsy

Loss of blink and corneal reflex

Dry eyes, need eye drops

Infection likely

Question 21

What happens if you get paralysis of levator palpebrae superioris?

Answer 21

Innervated by CN III - occulomotor nerve

Drooping of the upper eyelid - known as ptosis

Vision compromised

Residual opening of the eye due to superior tarsal muscle (smooth muscle)

Question 22

What happens if you get paralysis of superior tarsal muscle?

Answer 22

Sympathetic innervation

It is smooth muscle

Minor drooping of the upper eyelid - known as partial ptosis

Vision usually ok

Eye opening is ok due to levator palpebrae superioris

Can be caused by Horner’s syndrome (with pupil constriction, etc…)

Question 23

Describe lacrimation

Answer 23

Lacrimal fluid (tears) is created by lacrimal glands in superior lateral border of the eye

Eyes close lateral to medial, tears collect at lacrimal lake (medial canthus)

Tears production:: parasympathetic fibres of facial nerve, CN VII

Sensory supply via lacrimal branch of the ophthalmic division of CN V (also to eyelid and conjunctiva)