The Orbit And The Eyeball

Question 1

What is the angle between the two lateral walls?

Answer 1

90*

Question 2

Angle between the medial walls?

Answer 2

Nearly parallel

Question 3

Angle between the optical axes? Which direction?

Answer 3

Parallel

Directly anteriorly

Question 4

Which bones form the walls of the orbit?

Answer 4

Roof: frontal and sphenoid bone
Floor: maxilla, zygomatic and palatine
Medial: ethmoid, maxilla and lacrimal
Lateral: zygomatic and sphenoid

Question 5

What marks the apex of the canal and what does it contain? Where is it located?

Answer 5

The optic canal which contains the optic nerve

Lesser wing of the sphenoid bone just medial to the superior orbital fissure

Question 6

Which structures pass through the superior orbital fissure?

Answer 6

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Lacrimal nerve
Frontal nerve
Trochlear nerve
Superior branch of oculomotor nerve
Nasociliary nerve
Inferior branch of oculomotor nerve
Abducent nerve
Ophthalmic veins
Sympathetic nerves

Question 7

Where is there superior orbital fissure located?

Answer 7

Between greater and lesser wings of the sphenoid bone

Question 8

Where is the inferior orbital fissure found?

Answer 8

Between the inferior and lateral walls of the orbit

Between maxilla and sphenoid

Question 9

What passes through the inferior orbital fissure?

Answer 9

Infraorbital nerve

Question 10

What is the optic nerve surrounded by and why?

Answer 10

Cranial meninges because it is an extension of the brain

Question 11

What are the three layers of meninges?

Answer 11

Pia mater
Arachnoid mater
Dura mater

Question 12

Where does the optic nerve begin and end?

Answer 12

Retina of the eye to the primary visual cortex of the brain

Question 13

How is the optic nerve formed?

Answer 13

Convergence of axons from the retinal ganglion cells which receive impulses from the photoreceptors of the eye (rods and cones)

Question 14

What is the extracranial course of the optic nerve?

Answer 14

Leaves the bony orbit via the optic canal

Enters the cranial cavity along the surface of the middle cranial fossa (in close proximity to the pituitary gland)

Question 15

What is the intracranial course of the optic nerve?

Answer 15

Within the middle cranial fossa, the optic nerves from each eye unite to form the optic chiasm
Here, fibres from the nasal (medial) half of each retina cross over, forming the optic tracts
Each tract travels to its corresponding hemisphere

Question 16

What does each optic tract contain?

Answer 16

Left optic tract - fibres from left temporal (lateral) retina and right nasal (medial) retina
Right - fibres from right temporal retina and left nasal retina

Question 17

How can a pituitary adenoma affect vision?

Answer 17

Pituitary gland is close to the optic chiasm

Compression particularly affects fibres which cross over from the nasal half of each retina.

Question 18

If fibres which cross over from the nasal half of each retina are affected, what happens to vision?

Answer 18

Defect in the peripheral vision of both eyes - bitemporal hemianopia

Question 19

How is the pituitary gland accessed?

Answer 19

Via sphenoid sinuses

Question 20

Which walls are most likely to break in a blow to the eye?

Answer 20

Inferior and medial walls

Question 21

What may a fracture of the medial wall involve?

Answer 21

Ethmoidal and sphenoidal sinuses

Question 22

What can infraorbital bleeding cause from a fracture?

Answer 22

Exophthalmos

Question 23

What is a blowout fracture?

Answer 23

Indirect traumatic injury that displaces the orbital walls

Question 24

What are the medial walls of the orbit separated by?

Answer 24

The ethmoidal sinuses and the upper part of the nasal cavity

Question 25

What complications can a blow out fracture lead to?

Answer 25

Muscle entrapment (inferior rectus)
Diplopia
Infection

Question 26

What is the main blood supply to the orbit?

Answer 26

Ophthalmic artery, a branch of the internal carotid
Gives rise to the central artery of the retina which pierces the sheath of the optic nerve and runs with it, emerging at the optic disc

Question 27

Which artery supplies the orbital floor?

Answer 27

Infraorbital artery, a branch of the external carotid

Question 28

Blockage of which artery can cause blindness?

Answer 28

Ophthalmic artery

Question 29

Venous drainage of the orbit?

Answer 29

Superior and inferior ophthalmic veins which exit through the superior orbital fissure and enter the cavernous sinus
Central vein of the retina which either enters the cavernous sinus directly or joins the ophthalmic vein

Question 30

What can occlusion of these veins cause?

Answer 30

Slow, painless loss of vision

Question 31

How can infection of the eye spread to the brain?

Answer 31

Via the veins

Question 32

Which veins return aqueous humour to central circulation?

Answer 32

Scleral venous sinus which encircles the anterior chamber of the eyeball

Question 33

What is the danger triangle of the face concerning infection?

Answer 33

Facial vein communicates with the cavernous sinus via the ophthalmic veins which is a possible route for spread of infection

Question 34

What can cause infection in the cavernous sinus?

Answer 34

Cavernous sinus thrombosis
Meningitis
Brain abscess

Question 35

What are some branches of the ophthalmic artery and where do they supply?

Answer 35

Short and long ciliary arteries - external aspect of the eye
Central retinal artery
Lacrimal artery - lacrimal gland, eyelids, conjunctiva
Posterior ciliary artery - posterior external eye
Muscular branches - extraocular muscles
Other branches to the ethmoidal and frontal sinuses, eyelids, forehead, scalp