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Hannah's Neuro > Contents of the Orbit > Flashcards

Contents of the Orbit Flashcards

1
Q

Which bone/s form the supraorbital margin?

A

Frontal bone

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2
Q

What is the role of the supraorbital notches?

A

Previously foraminae, frontal nerves pass here

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3
Q

Which bone/s form the infraorbital margin?

A

Zygomatic bone laterally

Maxilla medially

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4
Q

Which bone/s form the roof of the orbit?

A

Frontal bone

Less wing of sphenoid

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5
Q

Which bone/s form the floor of the orbit?

A

Zygomatic
Maxilla
Palantine

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6
Q

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

A

Zygomatic

Greater wing of sphenoid

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7
Q

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

A

Maxilla
Lacrimal bone
Ethmoid
Body of sphenoid

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8
Q

On which wall of the orbit do fractures typically occur?

A

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

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9
Q

What structures form the superior orbital fissure?

A

Greater and lesser wing of sphenoid

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10
Q

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

A

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

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11
Q

Describe the pattern of collagen in the sclera

A

Laid down in “whirls” for added strength

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12
Q

Where is the cornea and what is its role?

A

Makes up the anterior 1/6th of the eyeball

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

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13
Q

List the 5 layers of the cornea

A 
Epithelium (mucous membrane)
Bowman's layer
Stroma (collagen, continuous with the sclera)
Descemet's membrane
Endothelium
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14
Q

What characteristics of the cornea make it optimal for vision?

A

Avascular

Transparent

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15
Q

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

A

Not like blood vessels (don’t dilate)

Specialised to control water balance in the cornea

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16
Q

How is collagen laid down in the cornea?

A

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

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17
Q

List 3 factors which influence scleral opacity

A

Composition of the stroma
Hydration
Size and distribution of collagen

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18
Q

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

A

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

19
Q

What is the anterior chamber angle?

A

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

20
Q

What is one cause of glaucoma?

A

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

21
Q

List the 4 key structures in the anterior chamber angle

A

Cornea
Trabecular meshwork
Canal of Schlemm
Ciliary body

22
Q

How does the aqueous humour drain from the eye?

A

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

23
Q

What is the uvea?

A

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

24
Q

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

A

Iris
Ciliary body
Choroid

25
Q

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

A 
Formation of aqueous humour (via ciliary epithelium)
Tethers lens (via ciliary processes)
Performs accommodation (via ciliary muscle)
26
Q

Where is the aqueous humour produced?

A

By the 2 layers of ciliary epithelium lining the ciliary processes

27
Q

What is the role of the aqueous humour?

A

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

28
Q

What structures are responsible for accommodation of the lens?

A

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

29
Q

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

A

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
Q

What is the result of relaxation of the ciliary muscle?

A

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

31
Q

What is presbyopia and what is the underlying mechanism?

A

Loss of accommodation with age

Caused by a reduction in the flexibility in the lens capsule and zonules

32
Q

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

A

Sphincter pupillae: constricts pupil, innervated by PNS

Dilator pupillae: dilates pupil, innervated by SNS

33
Q

Describe the structure and function of the choroid

A

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

34
Q

List the 5 important structures of the retina

A 
Optic nerve/disc
Fovea/foveola
Macular
Posterior pole
Orra serrata
35
Q

What is the fovea?

A

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

36
Q

hat forms the optic nerve?

A

Axons of ganglion cells exiting the retina

37
Q

What is the lamina cribosa?

A

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

38
Q

What is the pathological relevance of the lamina cribosa?

A

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

39
Q

Which major blood vessels supply the orbit?

A

Tributaries of the opthalmic artery

Central retinal artery (CRA)

40
Q

Which artery is visualised in fundoscopy?

A

CRA

41
Q

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

A

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
Q

Describe the dual blood supply of the retina

A

CRA: to inner retina

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

43
Q

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

A

Orbicularis oculi: depresses upper lid, innervated by CNVII

Levator palpebrae superiorosis: elevates upper lid, innervated by CNIII

44
Q

What structures are contained within the lacrimal apparatus?

A

Lacrimal glands and ducts

Nasolacrimal sac and duct

Hannah's Neuro (31 decks)

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