Week 5 - Orbit anatomy

Question 1

Which bone makes the superior orbital ridge?

Answer 1

-Frontal

Question 2

Which bone makes the inferior orbital ridge?

Answer 2

-Zygomatic and maxilla

Question 3

Name the boundaries of the orbit

Answer 3

• Apex = optic canal
• Superior = Frontal and Sphenoid
• Lateral = zygomatic and sphenoid
• Medial = ethmoid, maxillary, lacrimal and sphenoid
• Inferior = maxillary and zygomatic

Question 4

Which boundary of the orbit is the thinnest?

Answer 4

-Medial

Question 5

What runs through the optic canal?

Answer 5

• Optic nerve

- Ophthalmic artery

Question 6

Name the foramina of the bony orbit

In which bone do they lie?

Answer 6

• Optic canal
• Superior orbital fissure
• Inferior orbital fissure
• Sphenoid

Question 7

What runs through the superior orbital fissure?

Answer 7

• CNIII
• CNIV
• CNV1
• CNVI
• Superior ophthalmic vein

Question 8

What is a blow out fracture? How does it present? How is it treated?

Answer 8

• Fracture to the inferior border of the orbit causing inferior rectus (and other muscles) to herniate into maxillary sinus
• Patient will have a history of blow to the eye and will be unable to look up
• Steroids and antibiotics (sometimes requires surgery)

Question 9

Why is it crucial the iris is able to contract and dilate?

Answer 9

• Allow different amounts of light into the eye
• Dilates in the dark to allow more light to enter
• Contracts in the light to prevent too much light from entering and damaging the retina

Question 10

What is the function of the lens?

Answer 10

-Focus the light into the retina

Question 11

Name the 3 layers of the eyeball and their constituents

Answer 11

• Outer fibrous -> Cornea, Sclere
• Middle vascular -> Ciliary body, Iris, choroid
• Inner -> retina, macula

Question 12

Why is there a blind spot in the eye?

Answer 12

-optic disk where optic nerve enters

Question 13

What is visual acuity?

Answer 13

-Clarity of vision

Question 14

What is the ciliary body?

Answer 14

• Part of the eye which includes the ciliary muscle.

- Accommodation (involving contracting/relaxing the iris) and produces/resorps aqueous humor

Question 15

What is the retina?

Answer 15

-Inner most layer of the eye which contains photoreceptors (cones and rods) which transmit chemical and electrical impulses down optic nerve

Question 16

What is the sclera?

Answer 16

-White of the eye -> Protective fibrous layer of the eye containing collagen and elastic fibres

Question 17

What is the choroid?

Answer 17

• Vascular layer of the eye containing connective tissue which lays between retina and sclera
• Functions to provide oxygen and nourishment to the outer layers of the eye

Question 18

What is the macula?

Answer 18

-Oval shaped pigmented area of retina which is the place of most visual acuity

Question 19

What is accommodation?

Answer 19

-Changes in lens shape (more convex or concave) to focus light from objects at different distances in order to maintain a clear image

Question 20

What is the cornea? Why is it avascular

Answer 20

• Transparent front part of the eye which covers the iris and the lens
• Refracts light to generate optical power
• Avascular so it is transparent

Question 21

What is the iris?

Answer 21

-The coloured part of the eye which contracts and relaxes to adjust the amount of light reaching the lens

Question 22

What is retinal detachment? Why can it occur?

Answer 22

• Trauma to the face can cause the retina to become detached from the eyeball causing flashes/blurring in unilateral vision.
• Can occur as the retina and choroid have different embryological origins-> initially separated by intraretinal space but enentually fuse together -> leaves weak area

Question 23

Can retinal detachment always be fixed?

Answer 23

-There is a time sensitive window to fix it

Question 24

Why is photophobia experienced in meningitis?

Answer 24

-Optic nerve is a brain tract (outpouching of brain) and thus is surrounded by meninges (pia, arachnoid and dura mater)

Question 25

Describe the segments/chambers of the eye

Answer 25

- Eyeball split into anterior and posterior segments -> posterior segment is behind the lens - Anterior segment separated further into anterior and posterior chambers -> divided by ciliary body

Question 26

What is the function of the aqueous humor of the eye?

Answer 26

-Provide oxygen and nutrients to the cornea and lens as it is avascular

Question 27

What produces the aqueous humor of the eye and how does it circulate?

Answer 27

- Produced by ciliary body to fill both the anterior and posterior chambers of the eye - Flows out through trabecular meshwork in the anterior chamber of the eye

Question 28

What is open angle glaucoma?

Answer 28

- Condition where the trabecular meshwork becomes blocked abd excess fluid accumulates between the cornea and the iris - Increases intraorbital pressure causing compression of optic nerve - Progressive painless vision loss

Question 29

What is a cataract?

Answer 29

-Hardening and flattening of the lens producing a reduced ability to focus vision and a glare as light scatters across the lens

Question 30

Name the muscles of the orbit and their nerve supply

Answer 30

- Superior oblique -> Trochlear nerve - Lateral rectus -> abducens - Inferior oblique, inferior/superior/medial rectus, levator palpabrae superioris -> Oculomotor

Question 31

What happens in a trochlear nerve palsy?

Answer 31

-Patient unable to look down and in (lost superior oblique)

Question 32

What happens if inferior oblique is damaged?

Answer 32

-Cannot look up and in

Question 33

Where does the central retinal artery come from?

Answer 33

-Ophthalmic artery

Question 34

Describe what happens in a central retinal artery occlusion

Answer 34

- Loss of blood supply to retinal of eye except for at macula as it receives its blood supply from choroid - Retina looks pale everywhere except macula

Question 35

Describe the venous drainage of the eye | Why is this clinically relevant?

Answer 35

- Central retinal vein -> Superior ophthalmic vein -> cavernous sinus - Means eye infection can track to brain

Question 36

What is papiloedema?

Answer 36

-Optic disk swelling caused by increased intracranial pressure which slows venous drainage from the eye -> usually bilateral

Question 37

How does central retinal vein occlusion differ from central retinal artery occlusion?

Answer 37

- Slow painful loss of vision -> will be rapid in artery | - Several haemorrhages seen on eyeball rather than pale

Question 38

Explain Lacrimal drainage

Answer 38

-Lacrimal gland -> lacrimal sac -> nasolacrimal duct -> inferior meatus

Question 39

What is the purpose of the eyelid?

Answer 39

-Protect from injury, excessive light and dryness

Question 40

Describe the conjunctiva

Answer 40

- Stratified columnar epithelium which covers inside of the eyelids and sclera which helps to lubricate the eye - Palpebral layer covers eyelid - bulbar layer covers sclera

Question 41

What is a meibomian cyst?

Answer 41

-Painless swelling of eyelid due to infection in the tarsal gland

Question 42

What is a sty?

Answer 42

- Infection of the cillary gland causing painful swelling of the eyelid - Usually caused by staph

Question 43

What muscle opens the eyelid?

Answer 43

-Levator Palpabrae Superioris | superior tarsal

Question 44

Which muscle closes the eyes?

Answer 44

-Orbicularis oculi