Eye and Orbit

Question 1

What is the definition of the orbit?

Answer 1

Bony cavity in the facial cavity that contains and protects the eyeballs and other associated structures.

Question 2

What occupies the rest of the space in the eye other than the eyeball?

Answer 2

Orbital fat

supports structures, keeps eyeball in the right place, allows for eyeball movement

Question 3

What is the difference between the shape of the orbit and the shape of the eyeball?

Answer 3

Orbit is pyramidal with an apex at the back.

Eyeball is spherical.

Question 4

What level is the apex of the orbit at?

Answer 4

At the level of the optical canal.

Question 5

What bones contribute to each of these orbital walls?

1) Superior
2) Medial
3) Lateral
4) Inferior

Answer 5

1) Frontal bone, contribution from lesser wing of sphenoid
2) Ethmoid bone, frontal bone and lesser wing of sphenoid
3) Zygomatic bone, greater wing of sphenoid
4) Maxilla bone, zygomatic bone and palatine bone contributions

Question 6

What are the 3 sinuses found around orbit?

Answer 6

Above orbit = frontal sinus

Below orbit = maxillary sinus

Medially to orbit = ethmoid sinus

Question 7

What is a surgical emphysema?

Answer 7

When air has gone into the orbit due to a blunt injury to the eye e.g. a ball or a fist

Question 8

What is the eyeball embedded in?

What is the eyeball supported by?

Answer 8

Eyeball is embedded in orbital fat.

Eyeball is supported by a hammock-like suspensory ligament.

Question 9

What 3 things protect the eyeball?

Answer 9

Eyelids
Tears
Conjunctiva

Question 10

How do the eyelids protect the eyeballs?

Answer 10

When the eyelid is closed, the eyeball is covered.
This protects the eye from injury and light.
Cornea is kept moist by spreading lacrimal fluid.

Eyelids are strengthened by bands of connective tissue called tarsus.
Embedded in the tarsal plates are the tarsal glands.
These glands are modified sebaceous glands that secrete an oily substance to increase the viscosity of tears and decrease evaporation rate.

Question 11

How does conjunctiva protect the eyeball?

Answer 11

Conjunctiva is a transparent mucosa membrane.
It is 1 cell layer thick and runs on the inside of the eyelid.

It is continuous with the conjunctiva that runs over the eyelid (bulba conjunctiva).

It contains very many small blood vessels.
This helps with an immune response.

Question 12

How do tears protect the eyeball?

Answer 12

Tears are produced by the lacrimal gland.

Production of tears is triggered by parasympathetic nerve impulses coming from the 7th cranial nerve.

This triggers secretion of lacrimal fluid through ducts onto surface of the eye.

Eyelids close in a diagonal way to help sweep tears across eye into drainage ducts called puncta.

Tears are 10 microbes thick over the cornea. They allow oxygen to diffuse from the air inwards.

Question 13

What muscles are found in the eyelid?

Answer 13

Levator palpebrae superior = found in upper eyelid.
Role is to raise the eyelid.
Innervates by CN3.

Superior tarsal muscle
= collection of smooth muscle fibres.
Role is to raise the eyelid.
Innervated by superior cervical ganglion.

Obicularis oculi = found in upper and lower eyelid.
Located in a subcutaneous tissue outside the tarsal plate.
Divided into the orbital part (broader part) and the palpable part (in eyelid).
Palpable part = important in closing eyelids in sleep and blinking.
Innervated by CN7.

Question 14

What are the 3 layers of the eyeball?

Answer 14

Outer layer = sclera
Middle layer = choroid
Inner layer = retina

Question 15

Explain the 3 layers of the eyeball

Answer 15

Sclera = tough and opaque. Provides attachment for all extra ocular and intrinsic muscles of eye. Avascular = white. Continuous with cornea.

Choroid = pigmented and highly vascular. Continuous with clearly body and iris.

Retina = light sensitive, neural part of eye

Question 16

What is the job of the cornea?

Answer 16

Where refraction of light occurs.
Innervated by V1 of trigeminal.
Will respond to dust particles to induce blinking.

Question 17

What is the vitreous chamber?

Answer 17

Eyeball is mainly composed of the vitreous chamber which has vitreous fluid in it. This is a transparent gel that is important to keep the shape of the eyeball.

Question 18

When in the choroid layer, we have the ciliary bodies.

Explain the role of this layer

Answer 18

Choroid layer is dark red. It is pigmented and highly vascular.

Choroid layer is continuous with the ciliary body.

The ciliary body is a ring structure that provides attachment for the lens with the zonular fibres.

Question 19

What is the role of the iris and the pupil?

Answer 19

Iris = lies on the anterior surface of lens and is a thin contractive diaphragm.

Pupil = has a hole inside for transmitting light.

Question 20

What are the two muscles that control the size of the pupil?

Answer 20

Dilator and sphincter papillae.

Dilator papillae are radically arranged and have sympathetic innervation.

Sphincter papillae are circularly arranged and have parasympathetic innervation.

Question 21

What does the ciliary muscle control in the eye?

Answer 21

Controls the lens to help us focus on different objects.

At rest, eye is naturally focused on an object 7m away. At rest, the lens is slightly stretched by the Zonules of Zinn fibres to make the lens flatter.

To focus on near objects, the ciliary muscles contract. This releases tension in the Zones of Zinn to allow the lens to have increased curvature so focal point slit closer.

More curved lens = can see closer.

Question 22

What are the 4 main movements of the eye?

Answer 22

Elevation = looking up

Depression = looking down

Medially = towards nose, ADDUCTION

Laterally = away from nose, ABDUCTION

Question 23

How many extra-ocular muscles are there that move the eye?

Where do these muscles attach from and into?

Answer 23

6

From the tendonous ring at orbit apex to different places on the sclera.

Question 24

Explain the two extra-ocular rectus muscles on sides

Answer 24

Lateral rectus and medial rectus.

Medial rectus contracting will pull eyeballs medially (adduction).

Lateral rectus contracting will pull eyeballs out laterally (abduction).

Question 25

Explain the two extra-ocular rectus muscles above and below

Answer 25

Superior and inferior rectus

Superior rectus contracts and this pulls the eyeball up (elevation).

Inferior rectus muscle contacts will push eyeball down (depression).

Question 26

Due to the positioning of the orbit angle compared to eye eyeball, what does a superior rectus muscle contraction also do?

Answer 26

Rotates the eye slightly medially (Adduction).

Question 27

Explain the two oblique muscles

Answer 27

Superior and inferior oblique muscles.

They do not attach to the tendinous ring at the apex.

They attach to the back of the eyeball and then to the front of the eyeball.

Superior oblique goes up and loops back to attach to the apex of eyeball. The loop anchors the superior oblique to the front of the eye.
The loop is called the trochlear.

Superior oblique muscle will rotate the eyeball to look laterally by also depression.

Inferior oblique causes elevation and abduction.

Question 28

How are the extra-ocular muscles innervated?

Answer 28

By CN3 except for 2 of the muscles.

Lateral rectus innervated the abducens (CN6).

Superior oblique innervated by the trochlear nerve (CN4).

Question 29

Where does the parasympathetic and sympathetic innervation come from?

Answer 29

Parasympathetic innervation (ganglion near periphery) comes from the ciliary ganglion.

Parasympathetic innervates the sphincter pupillae (pupil constriction) and ciliary muscle.

Sympathetic fibres = originate from the upper thoracic spinal cord (T1) and synapse in the superior thoracic ganglion onto post ganglion fibres which then run across the ciliary ganglion to eyeball.

Sympathetic innervates the dilator papillae and superior tarsal muscle (to lift eye lid).

Question 30

What nerve comes through the optical canal?

What nerve goes through the superior orbital fissure?

Answer 30

Optic canal = cranial nerve 2

Superior orbital fissure = 3,4,6 and V1.

Question 31

What artery supplies the eye and what foramen does it go through?

What does this branch from?

Answer 31

The ophthalmic artery through the optic canal.

This is a branch off the internal carotid artery.

Question 32

What are the 2 main veins of the orbit?

Answer 32

Inferior ophthalmic vein
Superior ophthalmic vein

Largely drain into the cavernous sinus.
Can also drain into the pterygoid plexus veins.

No valves in these veins so the blood can flow in any direction.
(means there is a route of bacteria to travel from a superior position on the face through to the cavernous sinus to spread the infection)