Contents of the Orbit Flashcards Preview

Hannah's Neuro > Contents of the Orbit > Flashcards

Flashcards in Contents of the Orbit Deck (44):
1

Which bone/s form the supraorbital margin?

Frontal bone

2

What is the role of the supraorbital notches?

Previously foraminae, frontal nerves pass here

3

Which bone/s form the infraorbital margin?

Zygomatic bone laterally
Maxilla medially

4

Which bone/s form the roof of the orbit?

Frontal bone
Less wing of sphenoid

5

Which bone/s form the floor of the orbit?

Zygomatic
Maxilla
Palantine

6

Which bone/s form the lateral wall of the orbit?

Zygomatic
Greater wing of sphenoid

7

Which bone/s form the medial wall of the orbit?

Maxilla
Lacrimal bone
Ethmoid
Body of sphenoid

8

On which wall of the orbit do fractures typically occur?

Medial wall (especially at the junction of the lacrimal and ethmoid bones)

9

What structures form the superior orbital fissure?

Greater and lesser wing of sphenoid

10

What is the role of the sclera? What % of the eyeball does it make up?

Maintains the shape of the globe by resisting internal and external forces, and provides attachments for EOMs
Makes up 5/6th of the eyeball

11

Describe the pattern of collagen in the sclera

Laid down in "whirls" for added strength

12

Where is the cornea and what is its role?

Makes up the anterior 1/6th of the eyeball
Principal refracting component (air-cornea interface is responsible for 60% of focussing)

13

List the 5 layers of the cornea

Epithelium (mucous membrane)
Bowman's layer
Stroma (collagen, continuous with the sclera)
Descemet's membrane
Endothelium

14

What characteristics of the cornea make it optimal for vision?

Avascular
Transparent

15

What is special about the endothelium of the cornea and what is its role?

Not like blood vessels (don't dilate)
Specialised to control water balance in the cornea

16

How is collagen laid down in the cornea?

In fibrils, uniform in diameter and evenly spaced
Run parallel to each other in bundles (lamellae), with 200-300 lamellae in the stroma
Adjacent lamellae lie at angles to each other

17

List 3 factors which influence scleral opacity

Composition of the stroma
Hydration
Size and distribution of collagen

18

When may injury to the cornea result in a corneal scar?

When the injury penetrates the stroma (repair of collagen may not exactly reconstruct the pattern of collagen deposition to maintain transparency)

19

What is the anterior chamber angle?

The junction between the iris and the cornea where the aqueous humour drains

20

What is one cause of glaucoma?

Defect in the drainage of aqueous humour via the anterior chamber angle, leading to increased pressure in the eye

21

List the 4 key structures in the anterior chamber angle

Cornea
Trabecular meshwork
Canal of Schlemm
Ciliary body

22

How does the aqueous humour drain from the eye?

Drains through the trabecular meshwork via the canal of Schlemm into the venous outflow

23

What is the uvea?

The middle coat of the eye, which provides the eye's vascular supply

24

What are the structures in the uvea, front of the eye to back?

Iris
Ciliary body
Choroid

25

What are the 3 functions of the ciliary body and what parts are responsible for each?

Formation of aqueous humour (via ciliary epithelium)
Tethers lens (via ciliary processes)
Performs accommodation (via ciliary muscle)

26

Where is the aqueous humour produced?

By the 2 layers of ciliary epithelium lining the ciliary processes

27

What is the role of the aqueous humour?

Maintains the health of the lens and cornea, and generates intraocular pressure

28

What structures are responsible for accommodation of the lens?

Zonules (anchored by the ciliary processes and attaching to the lens)
Ciliary muscles

29

What innervates the ciliary muscle? What is the result of contraction?

PNS (carried by CNIII)
Contraction of the muscle results in a loss of tension on the zonules; the lens "bulges" and this allows close-up objects to be better visualised

30

What is the result of relaxation of the ciliary muscle?

Zonules are pulled taut, the lens becomes thin and stretched out, and long distance objects are better visualised

31

What is presbyopia and what is the underlying mechanism?

Loss of accommodation with age
Caused by a reduction in the flexibility in the lens capsule and zonules

32

What are the 2 muscles of the iris? What are their respective functions and what is their innervation?

Sphincter pupillae: constricts pupil, innervated by PNS
Dilator pupillae: dilates pupil, innervated by SNS

33

Describe the structure and function of the choroid

3 layers of blood vessels including the choriocapillaris, which underlies the retina and supplies it with nutrients

34

List the 5 important structures of the retina

Optic nerve/disc
Fovea/foveola
Macular
Posterior pole
Orra serrata

35

What is the fovea?

Area of highest density of cones (no rods) providing high visual acuity

36

hat forms the optic nerve?

Axons of ganglion cells exiting the retina

37

What is the lamina cribosa?

Band of dense sieve-like collagen from the sclera (~1/3 of fibres) through which axons are transmitted

38

What is the pathological relevance of the lamina cribosa?

Can cause or exacerbate loss of ganglion cells in disease e.g. glaucoma

39

Which major blood vessels supply the orbit?

Tributaries of the opthalmic artery
Central retinal artery (CRA)

40

Which artery is visualised in fundoscopy?

CRA

41

List the 3 classifications of ciliary arteries supplying the orbit and describe their course

Anterior ciliary artery: feeds anterior structures once they get to the conjunctiva
Long posterior ciliary artery: pierces the globe, travels in the choroid to the front of the eye (supplies iris, ciliary body)
Short posterior ciliary artery: pierces the globe, travels in the choroid but stops at the optic nerve

42

Describe the dual blood supply of the retina

CRA: to inner retina
Posterior ciliary artery: to outer retina (i.e. photoreceptors)

43

What are the 2 muscles controlling the eyelid and what are their respective roles and innervations?

Orbicularis oculi: depresses upper lid, innervated by CNVII
Levator palpebrae superiorosis: elevates upper lid, innervated by CNIII

44

What structures are contained within the lacrimal apparatus?

Lacrimal glands and ducts
Nasolacrimal sac and duct