Anatomy of the Orbit

Question 1

List the bones that form the orbit?

Answer 1

• Frontal
• Sphenoid
• Lacrimal
• Maxillary
• Ethmoid
• Zygomatic

Question 2

3 foramina at the back of the orbit?

Answer 2

• Optic foramina
• Superior orbital fissure
• inferior orbital fissure

Question 3

Why are the medial wall and floor of the orbit weaker than the rim/other walls?

Answer 3

Because they are closely associated to paranasal air sinuses - only separated by a thin wall

Question 4

The eyeball itself is about 24mm long and the orbit is about 40mm long. What occupies the majority of this extra space?
Function?

Answer 4

Orbital fat

Mainly functions as a cushion

Question 5

What are the conjunctiva? Function?

Answer 5

The mucosal lining of the inner eyelid, also covers the sclera

Changes from skin to conjunctiva at margin of eyelid

Helps lubricate the eye by producing mucus and tears, also performs immune surveillance preventing microbes from invading the eye

Question 6

What is the name of the muscle that raises the top eyelid? Origin and insertion?

Answer 6

levator palpebrae superioris

Originates on the lesser wing of the sphenoid bone, inserts on the tarsal plate of the eyelid

Question 7

What gives structure to the eyelids?

What is it composed of?

Answer 7

The tarsal plate

Dense connective tissue

Question 8

What is the name of the glands associated with the tarsal plate? What do they secrete?

Answer 8

Meibomian glands

Secrete meibum, an oily substance that prevents evaporation of the eyes tear film

Question 9

Where are the conjuctiva located?

Answer 9

• Begins at the margin of the eyelid
• Continues along the eyelid and then loops back around to cover the sclera (area where it turns around called fornix)
• Covers the sclera, stops at cornea (doesn’t cover cornea)

Question 10

How does conjunctivitis present?

Answer 10

When the conjunctiva become inflamed the blood vessels of the usually transparent layer over the eye dilate

So the eye appears red

Also: itching & watery eyes

Question 11

What is the nerve that supplies parasympathetic innervation to the lacrimal gland?

Answer 11

Facial nerve (CN VII)

Question 12

Where does the lacrimal gland drain into?

Answer 12

Lacrimal duct

The superior fornix of the conjunctiva

eye

Question 13

Describe the passage of tears from the lacrimal gland

Answer 13

Lacrimal gland -> lacrimal duct -> surface of eyeball -> lacrimal punctum -> lacrimal canaliculi -> lacrimal sac -> nasolacrimal duct -> inferior meatus of nasal cavity -> absorbed in nasopharynx

Question 14

How does blinking promote the movement of tears into the lacrimal sac?

Answer 14

Since the orbicularis oculi muscles are over the lacrimal sac, blinking opens the sac and creates a negative pressure situation - drawing fluid into the sac

Question 15

What is the function of the intrinsic muscles of the eye? Of the extrinsic?

Answer 15

Intrinsic - Control pupil diameter and lens curvature

Extrinsic - move the eye

Question 16

What is the muscle responsible for lens accommodation? Where is it located?
Innervation?

Answer 16

Ciliaris muscle

Located in the ciliary body

CN III - oculomotor n.

Question 17

What are the muscles that control pupil diameter?

Answer 17

Constrictor pupillae and dilator pupillae

Question 18

What are the 6 extrinsic muscles of the eye? Fibre orientation for each?

Answer 18

Straight fibres from posterior:
- Superior, Inferior, Medial and Lateral RECTUS

Obliquely attached:
- Superior and inferior oblique muscles

Question 19

Describe the innervation of the extrinsic muscles of the eye

Answer 19

SO4 LR6 - rest 3

• Trochlear (IV) supples superior oblique
• Abducent (VI) supplies Lateral rectus
• All others: oculomotor n. (III)

Question 20

What are the cranial nerves that supply the orbit?

How do these nerves enter the orbit?

Answer 20

• Optic (II)
• Oculomotor (III)
• Trochlear (IV)
• Abducent (VI)

Enter through the superior orbital fissure, Except for optic which goes through the optic foramen
- Trigeminal V1 & V2 (V1 SOF, V2 IOF)

Question 21

Which branches of the trigeminal nerve supply the orbit?

Answer 21

Opthalmic and Maxillary

• V1 (opthalmic) through SOF
• V2 (maxillary) through IOF

Question 22

Which artery supplies blood to the orbit? Which carotid is it a branch of?

Answer 22

• Opthalmic artery

Branch of internal carotid

Question 23

Which artery supplies the inner layers of the retina? How does it get to the retina?
Which artery is it a branch of?

Answer 23

Central retinal artery - travels within the optic nerve to get to the retina (accompanied by vein)

Branch of opthalmic artery

Question 24

What is the optic disc?

Answer 24

Head of the optic nerve on the retina, physiological blind spot

Question 25

What investigation can let you see inside of the eye?

Answer 25

Opthalmoscopy / Fundoscopy

Question 26

How is the fundus of the eye segmented?

Answer 26

Divided into 4 segments, named based on whether they’re closer to nasal or temporal sided. Centre of the segments is the optic disc

• Lower nasal and temporal quadrants
• Upper nasal and temporal quadrants

Question 27

Which veins drain the eye and orbit?

What do they drain into?

Answer 27

Superior and inferior opthalmic veins

Drain into the cavernous sinus (right behind the orbit)

go through the SOF

Question 28

What do the intracranial venous sinuses lie between?

What do the sinuses collectively drain into?

Answer 28

The two layers of the dura mater

Drain into the internal jugular veins on each side