Anatomy of the Orbit

Question 1

How many bones make up the orbit?

Answer 1

7

Question 2

Name the seven bones which make up the orbit.

Answer 2

Frontal
Zygomatic
Lacrimal
Maxillary
Sphenoid
Ethmoid
Palatine

Question 3

There are three foramina which allow neurovascular structures to enter the orbit. Name them.

Answer 3

Optic foramen
Superior orbital fissure
Inferior orbital fissure

Question 4

The walls of the orbits are weak, especially the medial and inferior walls. Why is this?

Answer 4

Surrounded or adjacent to paranasal air sinuses

Question 5

Which paranasal air sinus is just above the orbit?

Answer 5

Frontal air sinus

Question 6

Which paranasal air sinus is just medial to the medial wall of the orbit?

Answer 6

Ethmoid air sinus

Question 7

Which paranasal air sinus is just inferior to the floor of the orbit?

Answer 7

Maxillary air sinus

Question 8

The eyeball is a lot smaller than the space of the orbit. What fills out the rest of the orbit?

Answer 8

Fat

Question 9

What is the length of eyeball compared to the length of orbit?

Answer 9

Eyeball- 24mm
Orbit- 40mm

Question 10

What does the fat in the orbit do?

Answer 10

Cushions the eyeball

Question 11

If you see someone with sunken eyeballs, what can this tell us?

Answer 11

They are late in the process of starvation as the fat supplies of the orbit are some of the last stores to be used.

Question 12

Compare the inside and outside of an eyelid.

Answer 12

Outside- skin
Inside- mucous membrane (conjunctiva)

Question 13

What does the tarsal plate (solid plate) of the eyelid do?

Answer 13

Keeps shape of eyelid

Question 14

What is the tarsal plate of the eyelid made of?

Answer 14

Dense connective tissue

Question 15

What is found within the tarsal plate?

Answer 15

Meibomian glands

Question 16

What is the function of meibomian glands?

Answer 16

Secretes oily substance which lines the tear film and prevents tears from evaporating

Question 17

Which muscles opens and closes the eyes?

Answer 17

Orbicularis oculi

Question 18

What happens if the Meibomian sebaceous glands are blocked?

Answer 18

Oily secretion is trapped inside and causes painful swelling

Question 19

What happens to the conjunctiva after it lines the inner side of the eyelid?

Answer 19

Turns on itself at a point called the fornix.

Therefore, there is a superior and inferior fornix, a fold in which the conjunctiva turns and covers part of the sclera.

Question 20

Why is the conjunctiva pink?

Answer 20

Many capillaries

Question 21

What does the conjunctiva not cover?

Answer 21

The cornea as needs the light

Question 22

What does the sclera have over it and how can you tell?

Answer 22

Conjunctiva- transparent but can see tiny blood vessels

Question 23

Which gland forms tears?

Answer 23

Lacrimal gland

Question 24

What is the parasympathetic innervation for the lacrimal duct?

Answer 24

Facial nerve (CN VII)

Question 25

What do the tears formed in the lacrimal gland coat?

Answer 25

Outer surface of sclera, conjunctiva and cornea. This is known as a tear film.

Question 26

What helps to spread the tear film around the anterior aspect of the eyeball?

Answer 26

Blinking

Question 27

What do tears drain through?

Answer 27

Punctae sitting at the medial side of each eyelid and then drains into the lacrimal sac.

Question 28

The lacrimal sac sits over the lacrimal bone. After the tears have drained into the lacrimal sac after the punctae, where do they drain to?

Answer 28

Through nasolacrimal duct into the inferior meatus.

Question 29

Just go over the pathway of tears.

Answer 29

From lacrimal gland -> coat eye -> drain into punctuae -> drain into lacrimal sac -> drain into nasolacrimal duct ->drain into inferior meatus

Question 30

What role does the orbicularis oculi have in tear production?

Answer 30

Squeezes lacrimal sac to release tears

Question 31

There are intrinsic and extrinsic ocular muscles. What do the intrinsic muscles help to control?

Answer 31

Control pupil diameter. Move the eye to look in different directions

Question 32

Which muscles in the iris help to constrict the pupil?

Answer 32

Sphincter pupillae (constrictor pupillae).

Question 33

Which muscles in the iris help to dilate the pupil?

Answer 33

Dilator puplillae

Question 34

What type of innervation causes pupils to dilate?

Answer 34

Sympathetic innervation

Question 35

Therefore, which type of innervation supplies the dilator pupillae?

Answer 35

Sympathetic innervation

Question 36

Which type of innervation will supply the constrictor pupillae and ultimately cause the pupil to contrict?

Answer 36

Parasympathetic inneration

Question 37

Which nerve carries parasympathetic innervation to the constrictor pupillae?

Answer 37

Oculomotor nerve (CN III)

Question 38

Name the three intrinsic muscles.

Answer 38

Constrictor/sphincter pupillae Dilator pupillae Cililiaris muscle

Question 39

What is the specific role of the ciliaris muscle?

Answer 39

Helps to alter lens to focus on closer objects.

Question 40

Which type of innervation supplies the ciliaris muscle?

Answer 40

Parasympathetic innervation -> both muscles beginning with C get parasympathetic innervation

Question 41

Which nerve supplies the parasympathetic innervation the the muscles of the eye?

Answer 41

CN III- oculomotor nerve

Question 42

What do extrinsic muscles do?

Answer 42

Muscles originate from the bony orbit and attach to the eyeball t help to move it.

Question 45

There are four straight extrinsic muscles called recti. Name them.

Answer 45

Medial rectus Lateral rectus Superior rectus Inferior rectus

Question 45

There are two oblique extrinsic muscles. Name them.

Answer 45

Superior oblique Inferior oblique

Question 46

Where do the recti muscles arise from?

Answer 46

Apex of the orbit from the annular fibrous ring.

Question 47

Which extrinsic oblique muscles enters the eye anteriorly?

Answer 47

Inferior oblique muscle

Question 48

Which extrinsic oblique muscles enters the eye posteriorly?

Answer 48

Superior oblique muscle

Question 49

There is another muscle which comes from the back of the orbit but attaches to the upper eyelid. What is it called?

Answer 49

Levator palpebrae superioris muscle

Question 50

What is the origin and insertion of the Levator palpebrae superioris?

Answer 50

Origin- roof of orbit Insertion- upper eyelid

Question 51

What is the origin and insertion of the rector muscles?

Answer 51

Origin- tendinous ring Insertion- sclera anteriorly

Question 52

What is the origin and insertion of the superior oblique muscle?

Answer 52

Origin- lesser wing of sphenoid Insertion- sclera posteriorly

Question 53

What is the origin and insertion of the inferior oblique muscle?

Answer 53

Origin- medial part of orbit floor Insertion- sclera posteriorly

Question 54

Which nerve supplies the superior oblique muscle?

Answer 54

Trochlear nerve (CN IV)

Question 55

Which nerve supplies the lateral rectus muscle?

Answer 55

Abducent nerve (CN VI)

Question 56

Which nerve supplies all the muscles of the eye except for the superior oblique and lateral rectus?

Answer 56

Oculomotor nerve (CN III)

Question 57

How many cranial nerves enter the orbit?

Answer 57

4

Question 58

Name the cranial nerves which enter the orbit.

Answer 58

Trochlear nerve (CN IV) Oculomotor nerve (CN III) Optic nerve (CN II) Abducent nerve (CN VI)