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SA head and neck > S8) Functional Anatomy of the Eye > Flashcards

S8) Functional Anatomy of the Eye Flashcards

1
Q

Describe the structure of the orbital cavity

A

The orbital cavity is pyramidal shaped with its apex pointing posteriorly and base anteriorly

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2
Q

Three openings at its apex transmitting nerves and blood vessels into and out of orbit.

Identify them

A
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3
Q

Identify 3 important anatomical relations of the orbital cavity

A
  • Paranasal air sinuses (maxillary and ethmoid)
  • Nasal cavity
  • Anterior cranial fossa
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4
Q

Identify two important implications of the anatomical relations of the orbital cavity

A
  • Orbital trauma
  • Spread of infection
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5
Q

Identify the different boundaries of the orbit

A
  • Roof (superior wall)
  • Floor (inferior wall)
  • Medial wall
  • Lateral wall
  • Apex
  • Base
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6
Q

Describe the structures forming the roof of the orbital cavity

A
  • The roof is formed by the frontal bone and the lesser wing of the sphenoid
  • The frontal bone separates the orbit from the anterior cranial fossa
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7
Q

Describe the structures forming the floor of the orbital cavity

A
  • The floor is formed by the maxilla, palatine and zygomatic bones
  • The maxilla separates the orbit from the underlying maxillary sinus
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8
Q

Describe the structures forming the medial wall of the orbital cavity

A
  • The medial wall is formed by the ethmoid, maxilla, lacrimal and sphenoid bones
  • The ethmoid bone separates the orbit from the ethmoid sinus
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9
Q

Describe the structures forming the lateral wall of the orbital cavity

A

The lateral wall is formed by the zygomatic bone and greater wing of the sphenoid

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10
Q

Describe the structures forming the apex and base of the orbital cavity

A
  • The apex is located at the opening to the optic canal (optic foramen)
  • The base (aka orbital rim) opens out into the face, and is bounded by the eyelids
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11
Q

Identify the weakest parts of the orbital cavity and explain why they are most easily fractured

A

Medial wall and floor as they are thinner and contain air cavities

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12
Q

What is an orbital blowout fracture?

A

An orbital blowout fracture is a fracture leading to the partial herniation of the orbital contents through the the orbital wall due to blunt force trauma to the eye

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13
Q

How does an orbital blow out fracture present?

A
  • Periorbital swelling (painful)
  • Double vision (especially on vertical gaze)
  • Impaired vision
  • Anaesthesia over affected cheek (infraorbital nerve damage)
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14
Q

How do orbital blow out fractures occur?

A

Sudden increase in intra-orbital pressure from retropulsion of eye ball e.g. by fist/ball fractures floor of orbit

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15
Q

What is the result of an orbital blow out fracture?

A
  • Orbital contents and blood can prolapse into maxillary and ethmoid sinuses respectively
  • The fracture site can ‘trap’ structures e.g. soft tissue such as the extra orbital muscle located near floor or orbit
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16
Q

Describe the structure and function of the eyelids (palpabrae)

A
  • Structure: consists of tarsal plates and muscles and have glands at their edges
  • Function: protect the eye when palpebral fissure is closed
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17
Q

Identify 5 contents of the orbital cavity

A
  • Lacrimal apparatus
  • Neurovascular structure
  • Orbital fat
  • Globe of the eye (eyeball) and its internal structures
  • Extra-ocular muscles
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18
Q

What do the tarsal plates do?

A

Tarsal plates provide a connective tissue skeleton to the eyelid for firmness and shape

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19
Q

What is the orbital septum?

A

Orbital septum is a thin sheet of fibrous tissue originating from orbital rim and blends with the tendon of LPS and tarsal plates

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20
Q

What does the orbital septum do?

A

The orbital septum separates intra-orbital contents from eyelid fat and orbicularis oculi

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21
Q

What is the clinical signficance of the orbital septum?

A

The orbital septum acts as a barrier against infection spreading from the pre-septal space to post-septal (orbital cavity proper)

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22
Q

What is periorbital cellulitis?

A

Periorbital cellulitis is the cellulitis of orbital structures which occurs secondary to infection from bites, periorbital trauma, sinuses (fronto-ethmoidal sinuses)

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23
Q

Identify 2 complications of periorbital cellulitis

A
  • Abscess formation
  • Intracranial spread of infection → cavernous sinus thrombosis
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24
Q

Describe the arterial supply of the orbit cavity

A

Arterial supply via ophthalmic artery and its branches

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25
Q

Describe the venous drainage of the orbital cavity

A

The veins of orbit drain to cavernous sinus, pterygoid venous plexus and facial veins

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26
Q

Describe the general sensory, special sensory and motor innervation of the orbital cavity

A
  • General sensory: opthalmic nerve (CN Va)
  • Special sensory: optic nerve (CN II)
  • Motor: oculomotor (CN III), trochlear (CN IV), abducens (CN VI)
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27
Q

Identify the glands of the eye

A
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28
Q

What is the Meibomian gland and what does it do?

A

Meibomian glands secrete a lipid-rich substance to lubricate the edge of the eyelids and mix the tear film over the surface of the eye to prevent tears from evaporating to quickly

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29
Q

What is a Meibomian cyst?

A

A Meibomian cyst (aka chalazion) is a lump in the eyelid caused by the blockage and resultant inflammation of the Meibomian gland

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30
Q

What is a stye?

A

A stye is a small painful lump in the inside of the eyelid due to the blockage of eyelash follicles

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31
Q

The lacrimal apparatus is also involved in secretion of tears into conjunctival sac.

Identify the specific structures involved

A
  • Lacrimal gland
  • Lacrimal caniculi
  • Lacrimal sac
  • Nasolacrimal duct
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32
Q

What does the lacrimal gland do, where is it found and how is it controlled?

A
  • The lacrimal gland secretes lacrimal fluid (tears)
  • It lies in the lacrimal fossa on the superolateral part of the orbit
  • It is under parasympathetic control via the facial nerve
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33
Q

Describe the process of secretion from the lacrimal gland

A
  • Lacrimal fluid enters the conjunctival sac through the lacrimal canaliculi and passes into the lacrimal lake at the medial angle of the eye
  • The fluid then drains into the lacrimal sac before passing into the nasal cavity via the nasolacrimal duct
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34
Q

What are the small holes on the medial side of the eyelid and what purpose do they serve?

A

There are two lacrimal puncta in the medial portion of each eyelid which function to collect tears produced by the lacrimal glands

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35
Q

What is the conjunctiva and what does it do?

A

Conjunctiva is a transparent, secretory mucous membrane which produces mucous and tears to lubricate the conjunctival and corneal surfaces

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36
Q

Describe the location and structure of the conjuctiva

A
  • Location: covers sclera and lines inside of eyelids, forming a conjunctival sac (does not cover over cornea)
  • Structure: highly vascular with small blood vessels within the membrane
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37
Q

What is conjunctivitis?

A

Conjunctivitis (aka pink eye) is an eye condition that causes redness and inflammation of the conjuctiva due to infection or allergy

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38
Q

What is a subconjunctival haemorrhage?

A

A subconjunctival haemorrhage (aka hyposphagma) is bleeding underneath the conjunctiva due to the rupture of one of the blood vessels in this mucosal layer

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39
Q

What is the physiological effect of blinking?

A

Blinking washes tear film across front of eye, rinsing and lubricating the conjunctivae and cornea

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40
Q

Which 3 structures maintain the position of the eyeball?

A
  • Suspensory ligament (sits underneath like a sling)
  • Rectus muscles
  • Orbital fat
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41
Q

The eyeball has three layers.

Identify and describe them

A
  • Outer: tough, fibrous sclera which continues anteriorly as transparent cornea
  • Middle: choroid which continues anteriorly as ciliary body and iris (vascular)
  • Inner: retina (inner photosensitive layer)
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42
Q

What does the sclera do?

A
  • Provides attachment for the extra-ocular muscles
  • Gives shape to the eyeball
  • Continous with the dural sheath covering the optic nerve
43
Q

Describe the structure and function of the ciliary body

A
  • Structure: vascular, muscular, consists of a ciliary process and muscle
  • Function: connects the choroid with the iris, produces aqueous humour (ciliary processes)
44
Q

Describe the general structure of the retina

A

The retina consists of an inner neurosensory layer and an outer pigmented epithelial cell layer

45
Q

What does the retina do?

A

The photosensitive layer of retina generates action potentials in response to light

46
Q

The pigmented layer lies between the choroid and neurosensory layer of the retina and its cells contain melanin.

What is the role of melanin?

A

Melanin absorbs scattered light that has passed into the eye, reducing reflection and allowing us to focus images appropriately on to the retina

47
Q

The neurosensory layer is the area of the retina that senses light and is where the photoreceptors (rods and cones) are found.

What is the role of the rod cells?

A

The rods are cells found in the peripheral parts of the retina, responsible for vision in low intensity light (night vision) and do not discern colours

48
Q

The neurosensory layer is the area of the retina that senses light and is where the photoreceptors (rods and cones) are found.

What is the role of the cone cells?

A

The cones are responsible for high visual acuity and colour vision and many are concentrated in an area of the retina called the macula

49
Q

What is the macula?

A

The macula is an area of the retina upon which acts as the centre of your vision and is visible on fundoscopy as a slightly darker area of the retina, lateral to the optic disc

50
Q

What is the fovea?

A

The fovea is the area at the very centre of the macula where the only photoreceptors are cones

51
Q

What is the palpebral fissure?

A

The palpebral fissure is the opening between the eye lids

52
Q

Label the structures 1-3 below in the eye:

A
53
Q

Label the structures 4-6 below in the eye:

A
54
Q

Label the structures 7-11 below in the eye:

A
55
Q

The eyeball has three chambers. Identify them

A
56
Q

Describe the contents of the different chambers of the eyeball

A
  • Vitreous chamber is filled with a transparent, jelly-like vitreous humour
  • Anterior and posterior chambers are filled with transparent aqueous humour
57
Q

What is aqueous humour and what does it do?

A

Aqueous humour is a substance secreted by the ciliary processes within ciliary body and nourishes the lens and cornea

58
Q

Describe the flow and drainage of aqueous humour

A
  • Flows from posterior chamber, through pupil into anterior chamber
  • Drains through iridocorneal angle (between iris and cornea) via trabecular meshwork into canal of Schlemm
59
Q

What is the canal of Schlemm?

A

The canal of Schlemm is a circumferential venous channel draining into venous circulation

60
Q

What is glaucoma?

A
  • Glaucoma is an eye condition due to the obstruction of the drainage of aqueous humour, leading to a rise in intra-ocular pressure
  • If left untreated glaucoma leads to irreversible damage and death of the optic nerve, causing impairment of vision or even blindness
61
Q

Drainage of aqueous humour from anterior chamber can be blocked.

Explain 2 possible ways this can occur

A
  • Trabecular meshwork deteriorates → open angle glaucoma (chronic – most common)
  • Narrowing of irido corneal angle → closed angle glaucoma (acute – less common)
62
Q

What is the iris?

A

The iris is a thin contractile diaphragm, located anteriorly to the lens, with a central aperture (the pupil) for transmission of light

63
Q

The iris gives the colour to the eye.

Apart from this, what else does it do?

A

Two muscles (sphincter and dilator pupillae) form the iris and control the size of the pupil, both of which are under the control of the ANS

64
Q

What is the lens?

A

The lens is a transparent biconvex structure enclosed in a capsule, lying posterior to the iris and attached to the ciliary body by the suspensory ligaments

65
Q

Describe the neurovascular supply to the lens

A

The lens is without nerve innervation or blood supply, receiving its nutrients entirely from the aqueous humour that surrounds and bathes it

66
Q

In four steps, describe the mechanism in which the retina responds to light

A

⇒ Light (photons) reaches the photosensitive retina

⇒ Photoreceptors (rods/cones) detect light

⇒ Action potentials are generated in response to light

⇒ Action potentials pass via ganglion cells whose axons collect in area of optic disc

67
Q

What is refraction?

A

Refraction is the change in direction of light on passing through boundary of two different mediums

68
Q

Light will be refracted as it passes through a number of structures and ‘fluids’ from outside eye towards retina.

Identify these structures

A
  • From air into liquid tear film → refract
  • Through cornea → refract
  • Through lens and vitreous humour before reaches retina
69
Q

Where does most refraction of light occur?

A

The most refraction of light occurs at the air-cornea interface

70
Q

Focusing near objects requires a greater refraction of light.

Why is this?

A

Light rays from near-objects are more divergent and require greater refraction to bring them into focus on retina

71
Q

Outline the accommodation reflex

A
  • Pupil constricts
  • Eyes converge & image is brought to focus on same point of retina
  • Lens becomes more biconcave (fatter)
72
Q

What are cataracts?

A

Cataracts are progressive opacities (clouding) occurring within lens leading to decreased vision

73
Q

What is presbyopia?

A

Presbyopia is the age-related inability to focus near-object as the lens becomes stiffer and less able to change shape

74
Q

What is papilloedema?

A

Papilloedema is a condition in which increased pressure in or around the brain causes the part of the optic nerve inside the eye to swell

75
Q

What is blepharitis?

A

Blepharitis is a common eye condition wherein the eyelids become red and inflamed often due to bacterial infection

76
Q

There are six extra-ocular muscles that attach to the globe of the eye, whose contraction causes movement and therefore control our direction of gaze.

Identify them

A
  • Lateral Rectus
  • Medial Rectus
  • Superior Rectus
  • Inferior Rectus
  • Inferior oblique
  • Superior oblique
77
Q

State the origin and attachment of the superior rectus muscle

A
  • Origin: common tendinous ring
  • Attachment: superior and anterior aspect of the sclera
78
Q

State the function and innervation of the superior rectus muscle

A
  • Function: elevation (slightly adducts and intorts)
  • Innervation: oculomotor nerve (CN III)
79
Q

State the origin and attachment of the inferior rectus muscle

A
  • Origin: inferior part of the common tendinous ring
  • Attachment: inferior and anterior aspect of the sclera
80
Q

State the function and innervation of the inferior rectus muscle

A
  • Function: depression (slight adduct and externally rotate)
  • Innervation: oculomotor nerve (CN III)
81
Q

State the origin and attachment of the medial rectus muscle

A
  • Origin: medial part of the common tendinous ring
  • Attachment: antero-medial aspect of the sclera
82
Q

State the function and innervation of the medial rectus muscle

A
  • Function: adduction
  • Innervation: oculomotor nerve (CN III)
83
Q

State the origin and attachment of the lateral rectus muscle

A
  • Origin: lateral part of the common tendinous ring
  • Attachment: anterio-lateral aspect of the sclera
84
Q

State the function and innervation of the lateral rectus muscle

A
  • Function: abduction
  • Innervation: abducens nerve (CN VI)
85
Q

State the origin and attachment of the superior oblique muscle

A
  • Origin: body of the sphenoid bone
  • Attachment: sclera of the eye, posterior to the superior rectus

its functional pull is from the trochlear

86
Q

State the function and innervation of the superior oblique muscle

A
  • Function: depression, abduction and medial rotation
  • Innervation: trochlear nerve (CN IV)

most powerful when the eye is already positioned medially

87
Q

State the origin and attachment of the inferior oblique muscle

A
  • Origin: anterior aspect of the orbital floor
  • Attachment: sclera of the eye, posterior to the lateral rectus
88
Q

State the function and innervation of the inferior oblique muscle

A
  • Function: elevation, abduction and lateral rotation
  • Innervation: oculomotor nerve (CN III)
89
Q

How does one test the function of the different extra-ocular muscles clinically?

A
90
Q

Label the following structures on this image of the retina:

  • Artery
  • Vein
  • Optic disc
  • Macula
  • Fovea
A
91
Q

What are the different steps involved in examining the eye?

A
  • I = Inspection
  • VA = Visual acuity
  • F = Visual fields
  • R = Reflexes
  • O = Opthalmoscope
  • M = Movements
92
Q

why do we need two eyes?

A
  • binocular vision
  • wider field of vision and depth perception
  • both eyes just be aligned so light hits same spot on both eyes
93
Q

what is conjugate eye movement

A

coordination of both eye movement

94
Q

what is diplopia

A

double vision due to misalignment of two eyes

95
Q

LR6 SO4

A
  • Lateral rectus innervated by abducens
  • Superior oblique innervated by trochlear
  • rest are innervated by occulormotor
96
Q

what are the two axis involved in the eye

A
  • axis of the orbit
  • visual axis (where extra ocular muscles attach at an oblique angle)
  • they confer several actions of the eye
97
Q

which extra ocular muscles are stronger elevators and depressors when the eye is in the adducted position

A
  • strongest elevator: inferior oblique
  • strongest depressor: superior oblique
98
Q

which extra ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the abducted position

A

strongest elevator: superior rectus

strongest depressor: inferior rectus

99
Q

why might the abnormality of one muscle make a big different in gaze

A
  • muscles all contribute to an equal but opposite pull
  • if one muscle is weakened the other one is no longer antagonised
  • resting position of eyeball may deviate
100
Q

how to test a persons rectus muscles

A
  • move eye laterally (lateral rectus)
  • look up (superior rectus)
  • look down (inferior rectus)
101
Q

how to test person oblique

A
  • move eye medially (medial rectus)
  • Look up (inferior oblique)
  • look down (superior oblique)
102
Q

cranial nerve 3 palsies

A
103
Q

Cranial nerve 4 palsies

A
104
Q

cranial nerve 6 palsises

A
  • horizontal diplopia worse on the side that is effected
    *

SA head and neck (18 decks)

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