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Jess Head & Neck > 6.1: Anatomy of the Orbit and Eye > Flashcards

6.1: Anatomy of the Orbit and Eye Flashcards

1
Q

Describe the outer layer of the eye

A

The sclera and cornea

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2
Q

Describe the appearance and function of the sclera, which part of it is visible?

A

White, tough and structural. A site for muscle attachment and is relatively avascular

It;s anterior part is visible

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3
Q

Describe the appearance and function of the cornea

A

Transparent, protrudes is avascular and sensitive

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4
Q

Which nerves are involved in the corneal reflex?

A

Afferent: CN V1 (ophthalmic division) Efferent: CN VII (facial)

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5
Q

Which layer of the eye is vascular and what is it called? What lies within this layer?

A

The middle layer; known as the Uvuea

Comprises the choroid, ciliary body and iris

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6
Q

What are the clinical terms for a large and small pupil?

A

Mydriasis: large pupil Miosis: small pupil

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7
Q

Describe how the ANS influences the pupil

A

Parasympathetic: contracts the circular sphincter pupillae muscles Sympathetic: Contracts radial dilator pupillae

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8
Q

Describe the mechanism of action of phenylephrine on the eye

A

It’s an alpha-1 adrenergic agonist and has sympathetic activation which dilates the pupil

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9
Q

Describe the mechanism of action of tropicamide and atropine on the eye

A

Muscarinic receptor antagonists - blocks parasympathetic and causes dilation

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10
Q

Describe the mechanism of action of pilocarpine on the eye

A

Direct acting cholinergic parasympathomimetic and therefore has parasympathetic activation to constrict the pupil

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11
Q

Describe the neural layer of the eye

A

This is the inner layer; consisting of the retina which has optic and non-visual parts

Lecture: fundus, macula, optic disc

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12
Q

Which part of the eye constitutes the ‘blind spot’?

A

The optic disc

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13
Q

Where is the fundus in the eye and how can it be visualized?

A

Posterior part, visualized with ophthalmoscope/fundoscopy

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14
Q

Where is visual acuity highest?

A

The macula’s fovea centralis as it has the highest concentration of photoreceptors

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15
Q

Where is the macula and what significant structure is located within it?

A

The macula is near the centre of the retina (between the superior and inferior arcades; within it is a small central pit composed of closely packed cones called fovea centralis

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16
Q

Approximately how many rods and cones are there in the eye?

A

~120 mill rods ~6 mill cones

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17
Q

What visual symptom may arise from meningitis and why?

A

Photophobia (pain when looking at bright light), as the optic nerve is an extension of the brain and thus has a layer of meningeal covering

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18
Q

Define papilloedema

A

Swelling of the optic nerve

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19
Q

Where is the anterior and posterior chamber of the eye?

A

In the anterior segment:

Anterior: between the cornea and iris/pupil

Posterior: behind the iris/pupil and lens and in front of the ciliary body

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20
Q

Describe aqueous humour including its location, what produces it, it’s purpose and how it flows out

A

Aqeous humor is secreted by the ciliary body into the posterior chamber of thr anterior segment. Oxygen, nutrients and wastes are brought to and from the lens and cornea which are avascular. The watery fluid flows from the iris into the anterior chamber and out via the trabecular meshwork - and through Schlemm’s canal into the venous system

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21
Q

Where is vitreous humor and what does it attach to?

A

The vitreous chamber (posterior segment of the eye), attached to the retina at the macula, nerve and ora serrata

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22
Q

List the structures of the eye that light passes in anterior-posterior order. Where does the light inevitably focus?

A

Cornea, aqeuous humor, lens, vitreous humor and focusses on the fundus (fovea) of the retina

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23
Q

What is the clinical term ofr normal sightedness?

A

Emmetropia

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24
Q

Describe the refractive errors which occur in myopia and hypermetropia

A

lecture

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25
Q

Which structures form the boundaries of the orbit?

A

Medial: ethmoid, maxilla and lacrimal bones

Lateral: zygomatic and sphenoid

Roof: frontal and sphenoid

Floor: maxilla and zygomatic

Apex: optic canal

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26
Q

What happens in a blow out fracture?

A

Lecture

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27
Q

Name the eight muscles responsible for eye movement and the nerves that innervate them!

A

SO4LR6..ALL the rest 3!

Superior oblique: Trochlear CN IV

Lacteral rectus: Abudcens CN VI

Medial rectus, superior rectus, inferior rectus, inferior oblique and levator palebrae superioris: Oculomotor CN III

28
Q

List the primary, secondary and tertiary actions of the following muscles in order

a) superior rectus
b) inferior rectus
c) superior oblique
d) inferior oblique

A

a) elevation, intorsion, ADduction
b) depression, extorsion, ABduction
c) intorsion, depression, ABduction
d) extorsion, elevation, ADduction

29
Q

Which muscles are working in a 3rd nerve palsy of the eye? What might this condition be a first sign of?

A

Lateral rectus and superior oblique - “down and out”

May be first sign of posterior communicating artery aneurysm

30
Q

What causes the symptoms of a 3rd nerve palsy (and what are they)?

Name five other things which may cause this condition

A
  1. Ptosis (droopy upper eyelid): due to paralysed levator palpebrae superioris
  2. Dilated pupil: paralysed sphincter papillae of iris allowing unopposed action of iris dilator muscle
  3. Down and out eyes due to functioning superior oblique and lateral rectus muscles

May be due to ischemia, tumour, demyelination, vasculitis, congenital (or trauma)

31
Q

Which muscle of the eye is affected in a 4th nerve palsy?

A

Superior oblique

32
Q

How might an individual with a 4th nerve palsy of the eye present?

A

Vertical and horizontal diplopia (double vision) that is worse on downgazing. They may have a compensatory head tilt away and hypertropia (eye misaligment) on the affected side

33
Q

What are the primary actions of the lateral and medial rectus muscles?

A

Lateral: ABduction

Medial: ADduction

34
Q

Which muscle of the eye is affected in a 6th nerve palsy?

A

Lateral rectus

35
Q

How might an individual with a 6th nerve palsy present?

A

Can’t abduct the eye on the affected side. May have horizontal diplopia that is worse when looking to the affected side

36
Q

Label the following diagram

A

Lecture

37
Q

Which blood vessels supply the eye and which vessels do they arise from?

A

Inner retina: ICA -> Opthalmic artery -> central retinal artery (passes through the optic disc) -> multiple terminal branches (end arteries) to the eye, lacrimal gland and face

Outer retina:

38
Q

What happens if there is a retinal artery occlusion?

A

Since the central retinal artery gives off multiple TERMINAL branches, any occlusion/embolus ot the arteries supplying the retina will result in instant and total blindness

39
Q

Describe the venous drainage of the eye

A

Central retinal vein and choroidal veins drain mostly into -> superior opthalmic vein

-> superior and inferior opthalmic veins + pterygoid plexus -> cavernous sinus

40
Q

What do the eyelids protect against?

A

Injury, excessive light and dryness. They also keep the cornea moist by maintaining a film of tears as they blink

41
Q

Which structures are responsible for allowing the eye to open and close?

A

Open: Oculomotor CN III, levator palpebrae superioris, superior tarsal muscle/Muller’s - sympathetic (tightens LPS’s attachment and can raise the lid a few more mm)

Close: Facial n CN II - orbicularis oculi

42
Q

Where is the “blindspot” and why is it one?

A

The optic disc on the nasal side of the macula, it contains nerve fibres and no photoreceptor cells and is thus insensitive to light

43
Q

Which part of the eye forms the largest vascular layer of the eyeball? Describe its location and what it terminate anteriorly as

A

The choroid; a dark layer between the retina and sclera. Terminates anteriorly as the ciliary body

44
Q

Which part of the eyeball is musclular AND vascular? Which structures does it connect?

A

The ciliary body; connects the choroid with the iris

45
Q

Describe the contents and space of the posterior segment of the eyeball

A

Back 2/3, contains the vitreous humor, retina, choroid and optic nerve

46
Q

Where is the iris? Describe it

A

The anterior surface of the lens; it’s a thin contractile diaphragm with a central aperture (the pupil) for the transmission of light

47
Q

Where is the lens? Describe its structure and how one other structure can influence it’s shape

A

Posterior to the iris; a transparent biconvex structure enclosed in a capsule attached to the ciliary body by suspensory ligaments. Contraction of the muscle fibres in the ciliary body changes the shape of the lens

48
Q

Describe the structure of the retina - what process does it facilitate?

A

Facilitates the conversion of light into signals that can be sent to the brain

Outermost layer: darkly pigmented retinal pigment epithelium (RPE) which is firmly adherent to the underlying choroid

Resting on top (one layer in) is the neurosensory retina; consisting of an outer layer of photoreceptors cells (rods and cones)

Then there are multiple layers of nerve clel bodies and axons, with an innermost retinal nerve fibre layer which are transmitted to the brain via the optic nerve

49
Q

What forms the facial sheath of the eyeball? What is it continous with?

A

The periosteum (periorbita) lining the bones of the orbit, it’s continous at the optic canal and supraorbital fissure with the periosteal layer of the dura mater

Over the orbital margin and through the infraorbital fissure it’s continous with the periosteum covering the external surface of the cranium

50
Q

What provides mechanical strength to the eyelids?

A

Tarsal plates (dense bands of CT) which suspend the eyelids from the orbit and the medial and lateral canthi (corners)

51
Q

What is the function of the tarsal glands?

A

They secrete oils which maintain the tear film by helping to prevent evaporation

52
Q

What is a chalazion?

A

A non-infectious obstruction of a Meibomian/tarsal gland causing localised swelling

53
Q

What is a hordeolum (i.e stye)?

A

An acute, localized swelling due to infection in a meibomian/tarsal gland or eyelash follicle

54
Q

Where are the lacrimal glands?

A

Paired, almond-shaped exocrine glands that sit in the lacrimal fossae of the frontal lobe (superotemporal to the globe/eyeball)

55
Q

What do the lacrimal glands secrete?

A

The aqueous component of tears onto the surface of the eye.

56
Q

What happens to tears as the eye blinks?

A

They are swept medially and drain into the upper and lower canliculi found at the medial canthus. These canaliculi form the common canaliculus before joining the nasolacrimal duct which drains into the inferior meatus of the nasal cavity.

57
Q

Where do the lacrimal glands recieve innervation from?

A

Parasympathetic innervation from secreto-motor fibres from the greater petrosal branch of the facial nerve CN VII

58
Q

What constitutes a blowout fracture? How common is it?

A

It is produced by a blow to the orbit which sudden;y increases the intra-orbital pressyre and fractures a portion of the obrital bony lining (one of the walls or floor) with the orbital rim remaining intact. It’s the commonest orbital fracture

59
Q

Name five complications that may occur as a result of an orbital blowout fracture

A

Enophthalmos: posterior displacement of the eye as the orbit is decompressed by the fracture

Diplopia: double vision due to entrapment of extraocular muscles in the fractures

Globe injury

Facial numbness due to injury to the inferior orbital nerve

Orbital emphysema or hemorrhages

60
Q

What happens to the eye if the facial nerve becomes damaged?

A

Paralysis of the orbicularis oculi: this prevents the eyelid from clossing fully and loss of protective blinking. As a result, the cornea becomes dry and is left unprotected from dust and other particulate material

Chronic exposure to the cornea causes permanent scarring and visual loss

61
Q

Where do the recti muscles of the eye arise from and where is it?

A

The common tendinous ring which surrounds the optic canal at the posterior apex of the orbit

62
Q

Where does each of the oblique muscles arise from and insert?

A

Superior oblique: superior to the common tendinous ring -> along nasal side of orbit -> redirected towards globe through trochlea of superior oblique -> posterior aspect of the globe

Inferior oblique: maxilla on the orbital floor (inferonasally) -> posterior globe

63
Q

Where does levator palpebrae arise from and where does it insert?

A

Arises superior to the common tendinous ring at the orbital apex and inserts into the superior tarsal plate of the upper eyelid as the levator aponeurosis.

64
Q

Which nerves supply sensation to the structures in the orbit?

*identify which nerve provides sensation to the cornea

A

Optic CN II

Lacrimal, frontal, nasociliary and ciliary nerves of the ophtlamic division VI

Cornea: CN V1 (afferent branch of the corneal reflex!)

65
Q

What do patients with 3rd nerve palsies require urgent investigation for?

A

ICA/cavernous sinus aneurysms

Jess Head & Neck (13 decks)

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