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TK Yr 3 GP Ophthalmology > 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

Identify the different boundaries of the orbit

A
  • Roof (superior wall)
  • Floor (inferior wall)
  • Medial wall
  • Lateral wall
  • Apex
  • Base
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3
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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4
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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5
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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6
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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7
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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8
Q

The orbital cavity has 4 bony walls. Identify them.

A
  1. Base = Tough orbital rim
  2. Medial wall = Ethmoid bone
  3. Floor = Maxillary bone
  4. Roof = Orbital plates of frontal bone
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9
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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10
Q

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

A
  • Orbital surgery e.g. lobotomy
  • Spread of infection (into and out from orbit)
  • Orbital trauma
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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 of the orbit as they are thinner and contain air cavities ( they aren’t chunky bones) .: most vulnerable to fracture when there is direct impact to the front of the eye by a ball/ fist.

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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 blowout fracture occur?

A
  • Direct impact to front of eye e.g. ball/fist
  • Leads to sudden increase in intra-orbital pressure from traume to the eye/ orbit
  • Results in retropulsion of contents in the orbit e.g. eyeball
  • This fractures floor of orbit (maxilla) → orbital blow-out fracture
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14
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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15
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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16
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. muscles and soft tissue such as the extra orbital muscle located near floor or orbit
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17
Q

Look at the images and describe what is seen in the orbital blow out fracture?

A
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18
Q

In orbital blow out fractures, the mastoid is often fractured. Although the medial wall of the orbit made by the ethmoid bone is thinner than the floor of the orbit, what makes it stronger?

A
  • presence of walled air cells (anterior, middle, posterior and ethmoidal air cells) act as buttresses + convey an added strength to the medial wall.
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19
Q

What risk is there with the presence of air ethmoidal air cells in relation to the orbit?

A
  • air cells can be come infected (acute sinusitis) and due to their proximity to the orbit → infection can sometimes break through the thin lamina papyracea (part of ethmoid bone forming medial wall of the orbit) → .: track into the orbit → causing orbital cellulitis
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20
Q

Which nerve is at risk during an orbital blow out fracture?

A
  • infra-orbital nerve (branch of Vb of trigeminal nerve)
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21
Q

What is the management for orbital blow-out fracture?

A
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22
Q

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

Identify them

A
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23
Q

What structures are carried in the optic canal?

A
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24
Q

What structures are carried in the superior orbital fissure?

A
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25
Q

What structures are carried in the inferior orbital fissure?

A
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26
Q
A
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27
Q

What is the main arterial supply to the orbit and eye?

A
  • ophthalmic artery (branch of ICA)
  • branches of ophthalmic artery including central retinal artery (supplies retina)
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28
Q

What is the main venous drainage of the orbit and the eye?

A
  • ophthalmic veins (superior and inferior) connections with cavernous sinus, pterygoid plexus and facial vein
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29
Q

There are 2 blood supplies to the retina. What are they? What is the significance of these?

A
  1. Central retinal artery (branch of ophthalmic artery) → inner retina
  2. Ciliary arteries (branches of ophthalmic artery) → feed extensive capillary bed within choroid layer (choriocapillaries) → these then supply retina too → outer retina

Retina requires both circulations to function properly.

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30
Q

Describe the structure and function of the eyelids (palpabrae)

A
  • Structure: consists of skin, subcutaneous tissue, muscles, tarsal plates.
  • Function: protect the front of the eye
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31
Q

Which 2 key muscles are found running in the eyelid?

A
  1. Orbicularis oculi
  2. Levator palpebrae superioris
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32
Q

What does the orbicularis oculi do and what is it innervated by?

A
  • Closes the eyelid
  • Innervated by facial nerve CN VII
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33
Q

What does the levator palpebrae superioris do and what is it innervated by?

A
  • Retracts eyelid
  • Innervated by occulomotor nerve CN III
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34
Q

What do the tarsal plates do?

A

Tarsal plates are dense bands of connective tissue skeleton to the eyelid.

It strengthens and gives the shape of the eyelid.

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35
Q

There are several glands found within the eyelids. Identify 2.

A
  • Meibomian/ Tarsal glands within tarsal plate
  • Glands associated with lash follicle
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36
Q

What is the function of the Meibomian/ tarsal glands found within the tarsal plates?

A
  • Modified sebaceous
  • Provides a lipid layer of tear film
  • This to prevent tear evaporation too quickly + spillage over eyelid.
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37
Q

If the tarsal/ Meibomian glands gets blocked, what can you present with?

A
  • Meibomian cyst - presents as a lump within the eyelid
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38
Q

How does a Meibomian cyst present?

A
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39
Q

How can you treat Meibomian cyst?

A
  • ⅓ resolve spontaneously
  • Surgical incision if persists
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40
Q

What is the function of the glands associated with lash follicle?

A
  • sebaceous - secretes oily substance → nourishes the hair follicle
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41
Q

What can arise from infected eyelash hair follicle or sebaceous gland?

A

Stye

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42
Q

How does a stye present?

A
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43
Q

How can you treat a stye?

A
  • Warm compresses +/- oral antibiotics
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44
Q

What is blepharitis?

A
  • inflammation of eyelid margin
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45
Q

What are the causes of Blepharitis?

A
  • Staphyloccocus
  • Meibomian gland dysfunction
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46
Q

How does someone present with Blepharitis?

A

crusting, dry eye lids +/- swollen + red

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47
Q

How can we treat blepharitis?

A
  • Treat with warm compress and lid hygiene (clean up debris, helps gland drain normally)
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48
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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49
Q

What does the orbital septum do?

A

The orbital septum separates intra-orbital contents from muscle and subcutaneous tissue of eyelid.

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50
Q

What is the clinical significance 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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51
Q

What is the difference between pre-septal/ periorbital cellulitis and post-septal cellulitis?

A
  • Pre-septal cellulitis → infection inv. superifical tissues (anterior to orbital septum)
  • Post-septal cellulitis → infection inv. tissues within the orbit (posterior to orbital septum)
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52
Q

What is periorbital cellulitis?

A

Periorbital cellulitis is the cellulitis of orbital structures confined to skin and tissues of eyelid, superficial to orbital septum.

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53
Q

What can cause peri-orbital cellulitis?

A

occurs secondary to infection from bites, periorbital trauma, sinuses (fronto-ethmoidal sinuses)

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54
Q

How would peri-orbital cellulitis present?

A
  • Painful
  • Ocular function - all eye movements + function NORMAL
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55
Q

Identify 2 complications of periorbital cellulitis

A
  • Abscess formation
  • Intracranial spread of infection → cavernous sinus thrombosis
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56
Q

It can be difficult to differentiate between peri-orbital and the more severe orbital cellulitis. What should you do?

A
  • if any doubt, urgently refer
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57
Q

What is orbital/ post-septal cellulitis?

A
  • infection within the orbit (posterior or deep to orbital septum)
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58
Q

How does one present with orbital cellulitis?

A
  • Proptosis/ exopthalmous
  • Reduced +/- painful eye movements
  • Reduced visual activity - ‘blurred vision’
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59
Q

What could cause orbital cellulitis?

A
  • spread of infection from paranasal air sinus
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60
Q

What is the danger with orbital cellulitis?

A
  • orbital veins drain to cavernous sinus
  • potential route for infection to spread intracranially

resulting in :

→ cavernous sinus thrombosis

→ meningitis

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61
Q

How can we treat orbital cellulitis?

A
  • IV antibiotics
  • close monitoring to get infection under control
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62
Q

Describe the arterial supply of the orbit cavity

A

Arterial supply via ophthalmic artery and its branches

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63
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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64
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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65
Q

Identify the glands of the eye

A
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66
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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67
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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68
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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69
Q

Identify 6 contents of the orbital cavity

A
  • Lacrimal apparatus
  • Nerves
  • Blood vessels
  • Orbital fat (loads - protective)
  • Globe of the eye (eyeball) and its internal structures
  • Extra-ocular muscles
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70
Q

Which structures are involved in tear film production and draingage?

A
  • tear film and lacrimal apparatus
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71
Q

The tear film consists of 3 layers. What are they?

A
  1. Meibomian glands - OILY
  2. Lacrimal glands - WATER
  3. Goblet cells in conjunctiva - MUCUS
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72
Q

Blinking distributes tear film across the surface of the eye. What is the physiological effect of this?

A
  • Blinking washes tear film across front of eye, rinsing and lubricating the conjunctivae and cornea
  • (sweeping any dust + other foreign material across to the medial angle of the eye to be removed)
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73
Q

What is the purpose of the lacrimal apparatus?

A
  • series of structures that collect and drain tear fluid
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74
Q

If there is obstruction to drainage along the lacrimal apparatus, in particular the nasolacrimal duct, what can this result in?

A
  • Epiphora - overflow of tears over lower eyelid (‘excessive tearing of eye’)
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75
Q

How can there be obstruction in the lacrimal apparatus?

A
  • due to infection
  • injury
  • stenosis
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76
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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77
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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78
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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79
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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80
Q

What can happen if there are dirt or particles damaging the cornea?

A
  • Corneal abrasions
  • corneal ulcerations
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81
Q

Corneal abrasions and ulcerations can arise if there is dirt or particles damaging the cornea. How is the cornea recovered?

A
  • Outer epithelial layer of the cornea is constantly undergoing mitosis.: easily regenerates if damaged
  • However, if there are injuries deep into the cornea → can lead to permanent scarring + potential sig visual impairment
82
Q

How is the eyeball maintained in position?

A
  • Sensory ligament (sits underneath like a sling)
  • Extra-ocular muscles
  • Orbital fat ++
83
Q

Covering over the sclera is a thin transparent layer of cells called the ..

A

conjunctivae

84
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

85
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
86
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

Redness due to blood vessels dilating.

87
Q

What is the most common cause of conjunctivitis?

A

viral causes

88
Q

How would one present with conjunctivitis? Is it contagious?

A

Contagious - can spread to the pt’s other eye or other people!

89
Q

What is the treatment for conjunctivitis?

A
  • Reassurance
  • hygiene advice - washing hands/ not sharing towel etc
  • short course of topical choramphenicol eye drops - reduces risk of secondary bacterial infection
90
Q

Name an infective organism that can cause conjunctivitis esp from a mother giving birth.

A
  • Chlamydia - picked up from mother’s vaginal mucosa during birth → maybe a cause of conjunctivitis in the neonatal period
91
Q

What is the treatment for chlamydial conjunctivitis?

A

systemic antibiotics - erythromycin

92
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 often spontaneously in this mucosal layer

93
Q

How would one present with subconjunctival haemorrhage? Is it painful?

A
94
Q

How do we treat subconjunctival haemorrhage?

A
  • Looks more concerning that it acc is
  • Such haemorrhages are common
  • Just reassure pt that it will slowly resolve → much like a bruise would elsewhere on the body
95
Q

Name an example of a serious condition presenting as an acutely painful red eye?

A
  • Uveitis
96
Q

What is uveitis?

A
  • inflammation of the choroid layer

(uvea - collective term for choroid, ciliary process and iris)

97
Q

How do patients with uveitis present?

A
  • red painful eye
  • pain often worse when focussing / looking at bright lights
98
Q

What is uveitis typically associated with?

A

autoimmune conditions such as:

  • ankylosing spondylitis
  • inflammatory bowel disease
99
Q

How would we manage and treat uveitis?

A
  • If uveitis is suspected, pt must be referred urgently to ophthalmology for treatment (corticosteroids)
100
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) = uveal tract
  • Inner: retina (inner photosensitive layer)
101
Q

What does the sclera do?

A
  • Provides attachment for the extra-ocular muscles
  • Gives shape to the eyeball
  • Continuous with the dural sheath covering the optic nerve at the back of the eye
102
Q

What is sclera continuous of?

A

Sclera is continuous posteriorly with dura mater covering optic nerve.

103
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)
104
Q

Describe the general structure of the retina

A

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

105
Q

What does the retina do?

A

The photosensitive layer of retina converts the light energy into electrical impulses/ action.

106
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

107
Q

What are the photocreceptors?

A

rods and cones

108
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

109
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

110
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

  • point of highest acuity vision = central vision
111
Q

What is the fovea?

A

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

112
Q

There are 3 types of cones: red, green and blue which respond to diff light wavelengths. Absence/ dysfunction of one of these 3 cones can lead to …

A

colour blindness - an inherited condition that affects males more frequently than females

113
Q

Describe what happens once light is focused and reaches the photosensitive layer of the retina

A
  • Photoreceptors convert the light energy into electrical impulses
  • These reach the optic disc
  • The optic disc represents the accumulation of retinal axons that leave the eye as the optic nerve
114
Q

In central retinal artery occlusion, what occurs?

A
  • Ciliary branches are not affected as these are spared but remember, retina needs both blood supplies .: we get
  • sudden painless loss of sight in one eye, developing over seconds.
115
Q

How could central artery occlusion arise?

A

due to embolus causing occlusion

116
Q

What would the ophthalmoscope examination of the retina look like in someone with central artery stenosis and why?

A
  • underlying choroidal layer unaffected .: well perfused .: macula on top it comes out very red
  • whereas retina is pale - due to lack of supply coming from central retina artery
117
Q

What is the palpebral fissure?

A

The palpebral fissure is the opening between the eye lids

118
Q

Label the structures 1-3 below in the eye:

A
119
Q

Label the structures 4-6 below in the eye:

A
120
Q

Label the structures 7-11 below in the eye:

A
121
Q

The eyeball has three chambers. Identify them

A

Anterior chamber: space between the cornea and iris

Posterior chamber: space between the iris and the lens

122
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
123
Q

How does the anterior chamber connect with the posterior chamber?

A

via the pupil

124
Q

What is aqueous humour and what does it do?

A

Aqueous humour is a substance secreted by the ciliary processes within ciliary body found in the posterior chamber (fills both chambers via pupil) and nourishes the lens and cornea

125
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 + back into the venous circulation
126
Q

What is the irido-corneal angle?

A

space between the anterior surface of the iris and the posterior extremity of the cornea

127
Q

What is the canal of Schlemm?

A

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

128
Q

What does the ciliary body contain?

A
  • ciliary muscle and
  • ciliary processes
129
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
130
Q

How is the optic nerve affected in glaucoma?

A
  • In glaucoma → raised intra-ocular pressure → compresses + damages optic nerve
131
Q

We have two types of glaucoma. What are they? Which one is common?

A
  • Chronic → open-angle glaucoma - most common
  • Acute → closed-angle glaucoma
132
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)
133
Q

What causes open angle galucoma?

A
  • this is caused by blockage within the trabecular network (usually drains into aqueous humour into the canal of Schlemm)
134
Q

How does open-angle glaucoma present?

A
  • many asymptomatic (picked up on routine eye tests)
  • develops painlessly and insidiously over time - hard to pick up
  • Raised IOP - can be screened for in routine eye tests → see increased optic disc cupping and visual field loss esp peripheral vision
135
Q

How can we treat open-angle glaucoma?

A
  • topical medications (eye drops) - that reduce the production of aqueous humour e.g b-blockers e.g. Timolol and/or increase its drainage .: help reduce IOP
  • if these fail, surgery e.g. trabeculectomy may be needed
136
Q

Closed-angle glaucoma is less common. What causes this?

A
  • blockage due to narrowed iridocorneal angle ( narrowed by iris).
  • the access to the trabecular network is blocked off rather than within the trabecular network → results in rapid rise in intra-ocular pressure.
137
Q

How would one present with closed-angle glaucoma?

A
  • Sudden onset of painful red eye ++
  • blurred vision or halos around objects (due to corneal oedema)
  • fixed or sluggish, semi-dilated often irregular, oval-shaped pupil
  • nausea + vomitting
  • eye feels hard + tender to palpate through the upper eyelid
138
Q

What is dangerous about closed-angle glaucoma?

A
  • Ophthalmological emergency → requires rapid recognition and management → irreversible sight loss can occur within a few hours
139
Q

How do you treat closed-angle glaucoma?

A
  • diuretics e.g. acetazolamide - reduced aqueous humour production
  • muscarinic eye drops e.g. pilocarpine → usually causes pupillary constriction .: helps open the irido-corneal angle → improves route of drainage .: helps reduce IOP
  • strong analgesia
  • Surgical - making hole in the iris (irdotomy) with a laser (or surgically) → allows aqueous humour to flow freely from posterior chamber to anterior chamber
140
Q

Who is most at risk of closed-angle glaucoma?

A
141
Q

What would glaucoma look like through at opthalmoscope?

A
142
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

143
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

144
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

145
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

146
Q

What are cataracts?

A

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

As we age, degradation of the proteins in the lens → can cause it to become clouded and less transparent → cataracts

Treatment: surgery

147
Q

Light must reach and be focused onto the macula.

What regulates light entry?

Where does the light get refracted to be brought into focus?

What is the shape of the eyeball?

A
148
Q

What is refraction?

A

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

149
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
150
Q

Where does most refraction of light occur?

A

The most refraction of light occurs at the tear film-cornea interface

151
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

152
Q

What is the purpose of the accommodation reflex?

A
  • Helps to achieve greater refraction of light to bring image into focus when focusing near objects (the tear film and cornea can’t change .: lens will change - can thicken)
153
Q

Outline the accommodation reflex

A
  • Pupil constricts (limit amount of light coming through)
  • Eyes converge & image is brought to focus on same point of retina in both eyes
  • Lens becomes more biconcave (fatter) - by contraction of ciliary muscle
154
Q

contraction of the ciliary muscle is under the control of …

A

parasympathetic nervous system

155
Q

contraction of the ciliary muscle is under the control of …

A

parasympathetic nervous system

156
Q

What is presbyopia?

A

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

157
Q

How can presbyopia be corrected?

A

Glasses - to allow near-objects to be focused more comfortably

158
Q

What does phototransduction mean?

A
  • conversion of photons (light particles) to action potentials
159
Q

In five 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 (photoreceptors convert light signals into action potentials)

⇒ Action potentials pass via retinal ganglion cells whose axons collect in area of optic disc forming the optic nerve.

⇒ Action potentials propagated along visual pathway to occipital lobe for interpretation

160
Q

What is visual acuity?

A

ability of the eye to discern shapes and details of what you see

161
Q

How can you measure visual acuity?

A
  • measured formally using Snellen chart
  • Read set of letters of increasingly smaller size
  • Test one eye at a time
  • Pt reasons at 6m distance from the chart
162
Q

Normal vision using Snellen Chart is said to be…

A

Normal vision = 6/6

(at a 6m distance, individual is reading row of letters that corresponds with what we’d expect someone to be able to read at a 6m distance)

163
Q

What does the numerator and denominator depend on when measuring visual acuity?

A
164
Q

Initial inspection of the eye appears normal. The doctor tests distance visual acuity (VA) using a Snellen Chart. VA is recorded as 6/9 in the left eye and 6/18 in the right eye.

What does 6/9 and 6/12 mean…and in which eye is VA better?

A

Left eye is better - 6/9

Smaller the denominator - the greater

As numerator for both is 6. That is the distance they are standing from (6m). The value at the bottom is the row they can read from the Snellen chart → the smaller letters are found on a row that is of lesser number.

165
Q

What are 3 causes and examples of decreased visual acuity?

A
166
Q

How can we check transparency of the structures in the eye? (to see if this is the cause behind decreased visual acuity)

A

Shining ophthalmoscope into the eye and checking for ‘red reflex’ - normal

Absent → suggests light prevented from reaching retina and reflecting back.

167
Q

Which conditions can result in the absence of the red reflex?

A
  • Cataracts
  • vitreous haemrrhoage
  • retinoblastoma
168
Q

If there is nothing wrong with transparency of the eyes, we check to see if there are any refractive issues causing the decreased visual acuity. What refractive issues could be seen?

A
169
Q

If there are no transparency issues, no refractive issues, what could be concerning behind decreased visual acuity?

A
170
Q

How can we differentiate between refractive or non-refractive cause behind decreased visual acuity? Explain this

A
171
Q

What is papilloedema?

A

Papilloedema is a condition in which there is optic disc swelling due to an increased intracranial pressure.

172
Q

What could cause papilooedema?

A
  • things that cause an increase in ICP e.g. cerebral haemorrhage, tumour, meningitis
173
Q

Papilloedema can be associated with blurring of vision, which typically occurs in both eyes.

Why would blurring of vision involve both eyes (this does not relate to involvement of the optic chiasm…)?

A

Optic nerve - are extensions of the meninges.: any pressure in the brain i.e. raised ICP → will also affect the optic nerve

174
Q

How is papilloedema different from optic disc ‘cupping’?

A
  • Optic disc cupping → optic disc same size, optic cup bigger due to increased intra-ocular pressure ( pressure in eyeball)
  • Papilloedema → swelling of optic disc (optic disc bigger) due to increased intra-cranial pressure.
175
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
176
Q

State the origin and attachment of the superior rectus muscle

A
  • Origin: common tendinous ring
  • Attachment: superior and anterior aspect of the sclera
177
Q

State the function and innervation of the superior rectus muscle

A
  • Function: elevation
  • Innervation: oculomotor nerve (CN III)
178
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
179
Q

State the function and innervation of the inferior rectus muscle

A
  • Function: depression
  • Innervation: oculomotor nerve (CN III)
180
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
181
Q

State the function and innervation of the medial rectus muscle

A
  • Function: adduction
  • Innervation: oculomotor nerve (CN III)
182
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
183
Q

State the function and innervation of the lateral rectus muscle

A
  • Function: abduction
  • Innervation: abducens nerve (CN VI)
184
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
185
Q

State the function and innervation of the superior oblique muscle

A
  • Function: depression, abduction and medial rotation
  • Innervation: trochlear nerve (CN IV)
186
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
187
Q

State the function and innervation of the inferior oblique muscle

A
  • Function: elevation, abduction and lateral rotation
  • Innervation: oculomotor nerve (CN III)
188
Q

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

A
189
Q

Label the following structures on this image of the retina:

  • Artery
  • Vein
  • Optic disc
  • Macula
  • Fovea
A
190
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
191
Q

Overall ….

A
192
Q

Pathology involving which structures could present with blurring of vision in one eye?

A
  • lens → cataracts
  • cornea → abrasion/ ulcer
  • vitreous humour → haemorrhage / pus
  • macula → macula degeneration (occurs w age)
  • optic nerve → optic neuritis
  • refractive problems
  • astagmitism → eyeball change diff
193
Q

Name 2 common conditions that affect the lens.

A
  • Cataracts
  • Prebyopia (inability to change lens with age)
194
Q

As part of the eye examination, the doctor performs fundoscopy. Label the following structures on this image of a normal retina: a retinal artery (RA), retinal vein (RV), optic disc (OD) and macula (M)

A
195
Q

From which artery do the retinal arterial vessels arisen? How did this artery get into the back of the eye (given that the branches emerge in the region of the optic disc…gives a clue)?

A
  • ophthalmic artery → gives rise to the retinal arterial vessels
  • Retinal artery runs in the optic nerve
196
Q

A man attends the Emergency Department with an irritable, watery red right eye.

What is the diagnosis and why is the cornea not affected?

A

Diagnosis: Conjunctivitis

Cornea is not affected because it is not covered by the conjunctiva.

197
Q

Give three other causes for an acute red eye, that would present with pain.

A
  • closed angle glaucoma
  • abrasions to the conjunctiva/ eye → corneal abrasions/ ulcers
  • uveitis
198
Q

What is the ‘blind spot’?

A
  • the optic disc which contain no photoreceptors
199
Q

What chart do you use to check visual acuity?

A

Snellen chart

200
Q

Which test do you use to check colour vision?

A

Ishihara test

TK Yr 3 GP Ophthalmology (3 decks)

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