Orbit

Question 1

What are the bones of the orbit (skull)?

Answer 1

Anterior Cranial Fossa
Middle Cranial Fossa
Posterior Cranial Fossa
Maxillary Sinus (Inferior)
Nasal Cavity (Medial)

Question 2

What are the dimensions of the orbit?

Answer 2

35mm H x 40mm V
30mL volume
45-55mm axial length
25mm between

Question 3

From where to where is the axial length of the orbit measured?

Answer 3

Apex (optic canal) to Base (orbital margin)

Question 4

Describe the angles and positioning of the medial walls, lateral walls, optical axis, & orbital axis.

Answer 4

Medial walls separated by 25mm
Lateral walls form 90< and expose the eyes laterally to increase visual field
Orbital axis forms 45<
Optical axis is the axis that eyeballs look at

Question 5

What are the holes/bones of the orbit from top to bottom?

Answer 5

Supraorbital notch
Superior orbital fissure
Optic canal
Lacrimal fossa
Inferior orbital fissure
Infraorbital foramen

Question 6

What are the nerves of the superior orbital fissure?

Answer 6

Lacrimal Nerve
Frontal Nerve
Trochlear Nerve (4 motor)
Superior division of the oculomotor nerve (3)
Nasocilliary Nerve
Inferior division of the oculomotor nerve (3)
Abducens nerve (6 motor)
Superior ophthalmic vein
Part of inferior ophthalmic vein

Question 7

What is in the Tendinous ring of Zinn (muscle cone)?

Answer 7

Optic canal
Optic nerve (2)
Ophthalmic artery (branch of interior carotid)

Question 8

What are the nerves of the inferior orbital fissure?

Answer 8

Ganglionic branches (maxillary nerve)
Infra-orbital nerve (5b)
zygomatic nerve (5b)
Inferior ophthalmic veins
Infra-orbital artery
Infra-orbital vein

Question 9

What nerves are outside vs. inside the muscle cone?

Answer 9

Outside: L,F,T
Inside: S (levator, superior recuts) ,A,N,I (inferior oblique, inferior/medial rectus, pupillary fibers)

SO4 LR6, everything else 3

Question 10

What movements do the lateral, medial, superior and inferior rectus innervate?

Answer 10

Abduction
Adduction
Elevation
Depression

Question 11

What movements do the superior and inferior oblique innervate?

Answer 11

Intorsion
Extorsion

Question 12

What 3 muscles innervate lid position and what do they do?

Answer 12

Orbicularis oculi (7): close lid
Levator palpebrae superioris (3 sup.): elevate lid
Muller muscle (3 inf.): depression

Question 13

What lid muscle is controlled by the sympathetic NS?

Answer 13

Muller muscle

Question 14

What muscles form the muscle cone?

Answer 14

The recti muscles

Question 15

Which muscle does not originate from the back of the orbit?

Answer 15

Inferior oblique

Question 16

What is the purpose of the eye and visual system?

Answer 16

Transform light energy into neural signal to be perceived by the brain.

Question 17

What are the dimensions if the eyeball?

Answer 17

23.5mm H
24mm V
23-24mm axial length

Question 18

Compare steepness and radius of curvature of the sclera and cornea.

Answer 18

Cornea is steeper
Sclera has a higher radius of curvature (11.5mm vs. 7.8mm)

Question 19

What are the volumes of the anterior chamber, posterior chamber, vitreous, and total volume?

Answer 19

250ul anterior chamber
60ul posterior chamber
Vitreous 5-6mL
Total= 6.5mL

Question 20

What is the mass of the eyeball?

Answer 20

7.5g

Question 21

What is the carotid system?

Answer 21

Carries blood from heart to eye

Question 22

What is the ophthalmic artery?

Answer 22

First major branch of the internal carotid artery

Question 23

Where does the carotid artery branch what does it branch into?

Answer 23

Branches at the carotid bifocation into the external and internal carotid

Question 24

What is the carotid system?

Answer 24

Circulates the eye via ophthalmic artery
Anterior 2/3 of cerebral hemispheres

Question 25

What is the vertebrobasilar system?

Answer 25

Poster 1/3 of cerebral hemispheres including the occipital lobe
Brainstem (cranial nerves)
Cerebellum

Question 26

Circle of Willis

Answer 26

Links blood supply in the middle of the brain

Question 27

Retinal blood supply

Answer 27

2 blood supplies to satisfy high metabolic demand