Contents of the Orbit

Question 1

Which bone/s form the supraorbital margin?

Answer 1

Frontal bone

Question 2

What is the role of the supraorbital notches?

Answer 2

Previously foraminae, frontal nerves pass here

Question 3

Which bone/s form the infraorbital margin?

Answer 3

Zygomatic bone laterally

Maxilla medially

Question 4

Which bone/s form the roof of the orbit?

Answer 4

Frontal bone

Less wing of sphenoid

Question 5

Which bone/s form the floor of the orbit?

Answer 5

Zygomatic
Maxilla
Palantine

Question 6

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

Answer 6

Zygomatic

Greater wing of sphenoid

Question 7

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

Answer 7

Maxilla
Lacrimal bone
Ethmoid
Body of sphenoid

Question 8

On which wall of the orbit do fractures typically occur?

Answer 8

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

Question 9

What structures form the superior orbital fissure?

Answer 9

Greater and lesser wing of sphenoid

Question 10

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

Answer 10

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

Question 11

Describe the pattern of collagen in the sclera

Answer 11

Laid down in “whirls” for added strength

Question 12

Where is the cornea and what is its role?

Answer 12

Makes up the anterior 1/6th of the eyeball

Principal refracting component (air-cornea interface is responsible for 60% of focussing)

Question 13

List the 5 layers of the cornea

Answer 13

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

Question 14

What characteristics of the cornea make it optimal for vision?

Answer 14

Avascular

Transparent

Question 15

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

Answer 15

Not like blood vessels (don’t dilate)

Specialised to control water balance in the cornea

Question 16

How is collagen laid down in the cornea?

Answer 16

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

Question 17

List 3 factors which influence scleral opacity

Answer 17

Composition of the stroma
Hydration
Size and distribution of collagen

Question 18

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

Answer 18

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

Question 19

What is the anterior chamber angle?

Answer 19

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

Question 20

What is one cause of glaucoma?

Answer 20

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

Question 21

List the 4 key structures in the anterior chamber angle

Answer 21

Cornea
Trabecular meshwork
Canal of Schlemm
Ciliary body

Question 22

How does the aqueous humour drain from the eye?

Answer 22

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

Question 23

What is the uvea?

Answer 23

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

Question 24

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

Answer 24

Iris
Ciliary body
Choroid

Question 25

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

Answer 25

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

Question 26

Where is the aqueous humour produced?

Answer 26

By the 2 layers of ciliary epithelium lining the ciliary processes

Question 27

What is the role of the aqueous humour?

Answer 27

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

Question 28

What structures are responsible for accommodation of the lens?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

What is the result of relaxation of the ciliary muscle?

Answer 30

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

Question 31

What is presbyopia and what is the underlying mechanism?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

Describe the structure and function of the choroid

Answer 33

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

Question 34

List the 5 important structures of the retina

Answer 34

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

Question 35

What is the fovea?

Answer 35

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

Question 36

hat forms the optic nerve?

Answer 36

Axons of ganglion cells exiting the retina

Question 37

What is the lamina cribosa?

Answer 37

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

Question 38

What is the pathological relevance of the lamina cribosa?

Answer 38

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

Question 39

Which major blood vessels supply the orbit?

Answer 39

Tributaries of the opthalmic artery | Central retinal artery (CRA)

Question 40

Which artery is visualised in fundoscopy?

Answer 40

CRA

Question 41

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

Answer 41

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

Question 42

Describe the dual blood supply of the retina

Answer 42

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

Question 43

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

Answer 43

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

Question 44

What structures are contained within the lacrimal apparatus?

Answer 44

Lacrimal glands and ducts | Nasolacrimal sac and duct