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Head and Neck (Semester 5) > 6.1 Anatomy of the Orbit and Eye > Flashcards

6.1 Anatomy of the Orbit and Eye Flashcards

1
Q

Describe the pathway of light as it comes through the eye

A

Light comes in ➞ through cornea ➞ fluid filled space (anterior chamber) ➞ through iris (coloured/pigmented part) ➞ lens ➞ virtuous jelly ➞ retina

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2
Q

What is centre of the retina called and what is the function of this?

What is found at the centre of this area and do these areas compare to the rest of the retina?

A

The centre of the retina is marked by an area known as the macula. High acuity occurs at macula

The macula contains a depression called the fovea centralis, which has a high concentration of light detecting cells. This is where the very higher resolution of vision happens.

The rest of the retina have less resolving power, but gives us alot of our peripheral vision

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3
Q

What is the retina comprised of?

What happens when light passes through these structures?

A

The retina is comprised of rods and cones (photorecpeotrs) along with a thick bed of nerves which run along the inside of the eye.

When light passes through these nerves they all collect at the optic nerve and pass into the brain

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4
Q

What membrane found in the vascular layer of the eye is full of blood vessels

A

Choroid: provides nutrients to most of the eye

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5
Q

What is the outer, middle and Inner layer of the eye?

Briefly describe each

A

Fibrous Outer Layer: Sclera and Cornea

Middle Vascular Layer: Uvea (choroid, cillary body and iris)

Inner (Neural) Layer: Retina (photoreceptors)

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6
Q

Describe the components of the outer fibrous layer of the eye

A

Sclera:

  • white, tough, structural
  • muscle attachment, relatively avascular

Cornea:

  • transparent part, protrudes, avascular, sensitive
  • corneal reflex
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7
Q

What nerves are involved in the corneal reflex?

A

Afferent branch: CN V 1 (Ophthalmic Division)

Efferent branch: CN VII (Facial n.)

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8
Q

Describe the structure of the middle (vascular) layer of the eye

A

Uvea that is comprised of:

  • The choroid
  • The cillary body (produces fluid to keep the eye inflated)
  • the Iris

This layer is very rich with blood vessels

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9
Q

What is the Iris and state what the structure in the centre is

What is the innervation

A

The Iris is a thin diaphragm with an aperture in the centre which is the pupil.

Parasympathetic system contracts circular sphincter pupillae muscle

Sympathetic system contacts radial dilator pupillae

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10
Q

What is the name for a large vs small pupil?

A

Mydriasis – Large Pupil

Miosis – Small Pupil

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11
Q

Give 3 common eyedrops used to DILATE the pupil and incl their target and action

A

1) Phenylephrine:

  • Alpha-1 Adrenergic agonist
  • Sympathetic NS activation

2) Tropicamide:

  • Muscarinic receptor antagonist – Acetylcholine,
  • parasympathetic NS blockade

3) Atropine:

  • Muscarinic receptor antagonist – Acetylcholine,
  • parasympathetic NS
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12
Q

Give a common eyedrops used to CONSTRICT the pupil and incl its target and action

A

Pilocarpine

  • Direct acting cholinergic parasympathomimetic – Parasympathetic activation
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13
Q

What structure comprises the Inner (Neural) Layer of the eye

A

The inner layer of the eye is formed by the retina; its light detecting component

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14
Q

What is the name of the posterior of eye that can be seen with opthalmo- or fundoscope

A

Fundus

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15
Q

Where is the ‘blind spot’?

A

A small area lateral to the centre of the visual field where there is no visual perception

Corresponds to the optic disc (where the optic nerve passes through the surface of the retina). Here there are no photoreceptors

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16
Q

List the two types of photoreceptors and describe each

A

Rods:

  • Sensitive to low level light – night vision
  • All areas of retina except fovea
  • black and white

Cones:

  • Highest density at fovea
  • 3 different photopigments- red, green and blue
  • Daytime vision
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17
Q

Are rods or cones focussed at the macula and fovea?

A

Cones!!

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18
Q

Briefly describe the composition of the Retina and how light passes through?

A

The retina is composed of two layers:

  • Pigmented layer: continues around the whole inner surface of the eye.
  • Neural layer: consists of photoreceptors

Light passes through neural layers into the pigmented layers (at the bottom). The pigmented layer contains photoreceptors which help to keep the light in the eye (keeps image sharp). From here (following processing) it passes into the optic disc and into the brain

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19
Q

Describe the pathway of the optic nerve

A

The optic nerve is formed by the convergence of axons from the retinal ganglion cells.

These cells receive impulses from the photoreceptors (rods and cones)

After its formation, the nerve leaves the bony orbit via the optic canal (passageway through the sphenoid bone) and then enters the cranial cavity

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20
Q

Describe the structure of the optic nerve (CN II)

State the implication of this for meningitis

A

The optic nerve is an extension of the brain (brain tract). This means it has meningeal coverings (pia, arachnoid, dura). Within the Optic nerve is the central retinal artery and vein

If you have meningitis then photophobia could result (pain when looking at bright light) as a presenting symptom/sign

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21
Q

What is Papilloedema?

Give 2 causes and describe how it would appear under an orthoscope

A

Papilloedema: swollen optic disc (usually bilateral) due to high pressure in the brain

Could be due to anything causing high pressure within the brain such as trauma, aneurysm, tumour etc…

Appears red, big, swollen, hyperaemic

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22
Q

What is the location of the anterior and posterior chamber

A

Anterior: between cornea and iris/pupil

Posterior: between iris/pupil and lens/ciliary body

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23
Q

What are the 2 main fluids of the eye and describe each

A

1) Aqueous Humor: produced by ciliary body

  • watery fluid that provides nutrients for avascular cornea and lens
  • Maintains pressure of the eye

2) Vitreous Humor

  • Thick collagenous Gel in the vitreous chamber
  • Attached to retina at macula, nerve, ora serrata
  • Functions to provide support to the eye
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24
Q

The cornea is avascular (No BV), so how does it get its nutrients?

A

Aqueous humour

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25
Q

Describe the composition of vitrious humour

A

Thick gel that is 99% water with a framework of type II collagen and hyaluronic acid.

26
Q

label the anterior and posterior chamber vs segments on the image below

A

Note: the big orange at the back is the vitrious humor and the Ant and Post chambers contain the aqueous humour

27
Q

Describe the flow of normal aqueous fluid through the eye

A

Aqueous fluid produced by ciliary body
⬇
Oxygen, nutrients and wastes brought to and from lens/ cornea which are avascular
⬇
Travels to anterior chamber
⬇
Flows out via trabecular meshwork
⬇
Canals of Schlemm
⬇
Drains into venous system

28
Q

In open angled glaucoma what structures is the ‘angle’ between?

A

Between iris and cornea

29
Q

What is Open Angle Glaucoma?

How can this lead to blindness

A

OAG involves slow progressive thinning away of the nerve at the back of the eye due to high pressure in the eye

High pressure is caused by a miss-match between balance of aqueous humour (too much being produced or not enough being drained away). This means the outflow of aqueous humor through the trabecular meshwork is reduced leading to an increase in pressure.

This causes a gradual reduction of the peripheral vision, until the end stages of the disease (blindness)

30
Q

What is Closed Angle Glaucoma?

How can this lead to blindness

A

CAG is when the iris is forced against the trabecular meshwork, (iris comes forwards so the angle is reduced). This causes a mechanical resistance to flow and prevents drainage of aqueous humor.

There is also increased iris and lens contact so when the pupil dilates and constricts, the iris clumps up within the trabecular meshwork (can result in complete blockage)

This causes pressure to build up within the eye and eventually compress BV in eye/ BV’s supplying the nerve.

Emergency!! Can rapidly lead to blindness due to nerve damage

31
Q

List the 4 structures through which light passes

A

1) Cornea
2) Aqueous Humor
3) Lens
4) Vitreous Humour

*Light focussed on fundus (fovea) of retina

32
Q

What is the term used to describe normal sightedness?

Describe the angle light passes through normally

A

Emmetropia

Normally light enters parallel and then converges to focus on the back of the eye

33
Q

What type of abnormal eyesight do each of the following images show?

A
34
Q

What is the roof, floor, medial and lateral boarders of the Orbital bone?

A

Roof – frontal and sphenoid

Floor – maxilla and zygomatic

Medial – ethmoid, maxilla and lacrimal bones

Lateral – zygomatic and sphenoid

35
Q
A
36
Q

List 4 nerves that pass through the Superior orbital fissure (incl specific branches)

A

1) Occulomotor nerve- superior and inferior division (III)
2) Trochlear nerve (IV)
3) V1: Trigeminal nerve (frontal, lacrimal and nasocillary branches)
4) Abducens VI

37
Q

List one vein that passes through the superior orbital fissure

A

Superior Opthalmic vein

38
Q

List one nerve and artery which pass through the optic canal

A

Optic nerve and opthalmic artery

39
Q

What cranial nerve passes through the Inferior orbital fissue? (incl what 2 branches specifically)

A

Trigeminal nerve V2: the zygomatic and infraorbital branches

40
Q

What vein passes through the inferior orbital fissue?

A

Inferior opthalmic vein

41
Q

State the boundries of the bony orbit

A

Apex: optic canal

Superior (roof): frontal and sphenoid bone

Lateral: Zygomatic and sphenoid bone

Medial: ethmoid, maxillary, lacrimal and sphenoid bone

Inferior (base): maxillary and zygomatic bone

42
Q

What is a blowout fracture?

A

Partial herniation of the orbital contents through one of its walls. This usually occurs via blunt force trauma to the eye.

The medial and inferior walls are the weakest, with the contents herniating into the ethmoid and maxillary sinuses respectively.

43
Q

Where do all the muscles of the eye attach?

A

Spiral of Tillaux

44
Q

Which 5 eye muscles are supplied by CN III?

What are the 2 exceptions?

A

Oculomotor (CN III):

  • Medical rectus
  • Superior rectus
  • Inferior rectus
  • Inferior oblique
  • Levator Palpebrae Superioris (***)

Trochlear (CN IV): Superior oblique

Abducens (CNVI): 6. Lateral Rectus

45
Q

State the primary, secondary and tertiary action of each eye muscle

A
46
Q

Give 3 things that would be seen in a 3rd nerve palsy and explain why each occurs?

A

Ptosis: NO Levator palpebrae superioris

Mydriasis (blown pupil) : NO Sphincter Pupillae (PNS innervation travels with CN III)

Patient looking down and out:

  • NO Extraocular muscles (superior, middle, inferior rectus, and inferior oblique)
  • Lateral Rectus and Superior Oblique take over
47
Q

Give 4 causes of a 3rd nerve palsy

A

1) May be 1st sign of posterior communicating artery aneurysm
2) Ischaemia
3) Tumour
4) Trauma
5) Demyelination
6) Vasculitis
7) Congenital

48
Q

What 3 things would be seen in a 4th Nerve Palsy and why?

A

1) Hypertropia on affected side (one eye higher than fixating eye)

  • NO Superior oblique (usual function is intorsion and depression the eye)
  • Therefore, Inferior Oblique takes over and drags the eye up and in

2) Vertical and horizontal diplopia (double vision)

  • Worse on downgaze (walking downstairs) or reading
  • Due to misalignment of the eyes

3) Compensatory head tilt away from side of problem
* To reduce their diplopia

49
Q

What would be seen in a 6th Nerve Palsy and why?

A

1) Abduction deficit

  • Lateral Rectus affected
  • Can’t abduct the eye on affected side

2) Horizontal diplopia worse when looking to affected side

50
Q

Label the image below

A

A: CN III
B: Big Optic Nerve
C: CN III
D: CN IV
E: CN VI

51
Q

Label the image showing the eye muscle relationships to bones

A
52
Q

Describe the blood vessel supply to the eye?

A

Internal Carotid Artery → Ophthalmic Artery → Gives rise to Central Retinal Artery → Multiple terminal branches to eye, lacrimal gland, face

Remember these are terminal branches (end arteries) and thus have implications for blockages

53
Q

What is a Retinal Artery Occlusion and what is the consequence?

How would this appear on an opthalmoscopy?

A

Embolus in any of the arteries supplying retina. Results in instant and total blindness (typically in elderly)

Retina appears pale and vessels appear abnormal. Classical cherry red spot macula can be seen

54
Q

Describe the venous drainage of the eye

A

Central Retinal Vein → Drains to Superior Ophthalmic Vein → Superior and Inferior Ophthalmic Veins + Pterygoid Plexus → Cavernous Sinus

55
Q

Label the structures shown on the Lacrimal Apparatus

A
56
Q

How are the eyelids held togther?

A

The eyelids are held together with tarsal strips (structural bit of the eyelid)

We have both inferior and superior tarsus

57
Q

What 2 muscles lift the eyelid and what muscle closes it?

Incl their innervation

A

Lift eyelid:

  • Levator Superioris Palpebrae (CN III)
  • Superior Tarsal Muscle (Mullers) (SNS control)

Close eyelid:

  • Orbicularis Oculi (CN VII)
58
Q

Give 3 functions of the Eyelids

A

1) Protects Against Injury
2) Excessive Light
3) Dryness

59
Q

Lable the image of the eyelid

A
60
Q

What is the conjunctiva and what is the Limbus? (Incl the relationship between these)

A

Conjunctiva is a mucus membrane that sits on top of the eyeball. It functions to keep the eye moist and has an immune function (mucus and goblet cells)

As the sclera approaches the anterior portion of the eye it becomes the corneal limbus which then becomes the cornea. (limbus = border of the cornea and the sclera)

The limbus is where the clear stuff turns into conjunctiva which functions to coat the inner and outer surface of the eye and eyelid.

61
Q

List 2 things a blockage in a duct of the eye can lead to

A

callaseans or styes (infected hair follicle)

Head and Neck (Semester 5) (22 decks)

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