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3 - HNN > Functional Anatomy of the Eye > Flashcards

Functional Anatomy of the Eye Flashcards

1
Q

Describe the structures forming the walls of the orbital cavity

A
  • Roof - frontal bone, anterior cranial fossa, sphenoid bone
  • Lateral wall - zygomatic bone, sphenoid bone
  • Floor - maxilla, part of zygomatic bone
    • Below the floor of the orbit is the maxillary paranasal sinus - air filled cavity
  • Medial wall - ethmoid, maxilla, lacrimal, part of sphenoid
    - Ethmoid bone contains ethmoid air cells
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2
Q

What are the openings at the apex of the orbital cavity

A
  • Superior orbital fissure
  • Inferior orbital fissure
  • Optic canal
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3
Q

Outline which walls of the orbital cavity are most susceptible to fracture

A
  • Medial wall and floor of the orbit are the weakest parts of the orbital cavity as they contain paranasal air sinuses behind the bone
  • Fracture can break into sinus and cause infection to spread to and from orbit
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4
Q

What are signs and symptoms of orbital blow out fracture

A
  • History of trauma to the eye/orbit
  • Periorbital swelling, painful
  • Double vision - especially on vertical gaze
  • Impaired vision - restricted eye movement
  • Anesthesia over affected cheek (upper teeth and gums) on affected side
    • Infra-orbital nerve from maxillary nerve runs on orbital floor
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5
Q

What are the implications of a blow out fracture on the orbital contents

A
  • Sudden increase in intra-orbital pressure fractures floor of orbit
    • Retropulsion (forceful backward movement) of eyeball by fist or ball
  • Orbital contents and blood can prolapse into maxillary sinus
    • Fracture site can trap structures
    • Extra orbital muscle located near floor or orbit
  • Eye cannot look up due to trapped contents - prevents movement
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6
Q

State the connective tissue that form the eyelid

A
  • Eyelid (palpebrae) formed from superior and inferior tarsus
    • Provide a connective tissue skeleton to the eyelid - firmness and shape
  • Fibrous ring surrounding it - orbital septum
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7
Q

Explain the role of fibrous ring in the eyelid

A
  • Orbital septum
  • Thin sheet of fibrous tissue originating from orbital rim
  • Blends with tendon of LPS and tarsal plates
  • Separates intra-orbital contents from eyelid fat and orbicularis oculi muscle
  • Act as a barrier against infection spreading from the pre-septal space to post-septal space
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8
Q

Explain the presentation and complications of periorbital cellulitis

A
  • Secondary to infection from bites, periorbital trauma, sinuses (fronto-ethmoidal sinuses)
  • Pre-septal orbital cellulitis - in front of orbital septum
    • Localized infection and swelling
  • Complication include abscess formation and spread of infection intracranially
    • Cavernous sinus thrombosis - veins of orbit drain to cavernous sinus, pterygoid venous plexus and facial veins
  • Post-septal orbital cellulitis - infection can spread into orbital cavity
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9
Q

Describe the glands of the eyes and the pathology associated with each

A
  • Meibomian glands and glands of Zeis located on the edge of eyelids
  • Meibomian glands secrete oily substance onto edge of eye
    • Help prevent evaporation of tear film and tear spillage
    • Can block causing Meibomian cyst
  • Glands of Zeis are eyelash follicles
    - Can block causing styes
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10
Q

Outline the secretion and drainage of tears

A
  • Lacrimal apparatus involved in secretion of tears into conjunctival sac
  • Lacrimal gland - arranged around edge of levator palpebrae superioris
  • Lacrimal punctum drains conjunctivae into the lacrimal sac and down the nasolacrimal duct
    • Lacrimal sac located within the lacrimal fossa
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11
Q

Describe what conjunctivae is and how its tears affect it

A
  • Conjunctivae is a secretory mucosa lubricating the conjunctival and corneal surfaces
  • Blinking washes tear film across front of eye, rinsing and lubricating the conjuctivae and cornea
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12
Q

Explain the conjunctiva

A
  • Transparent mucous membrane that produces mucous and tears
  • Covers white of eye (sclera) and lines inside of eyelids (forming a conjunctival sac)
    • Does not cover over cornea
  • Highly vascular with small blood vessels within the membrane
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13
Q

Outline pathology of conjunctiva

A
  • Conjunctivitis - inflammation and infection
    • Pink eye
  • Haemorrhage from blood vessel readily visible as a subconjunctival haemorrhage
    - No treatment needed - just a bruise without skin
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14
Q

Describe the blood supply to and from the orbit

A
  • Main arterial supply through ophthalmic artery branching off internal carotid artery
  • Ophthalmic veins drain venous blood into cavernous sinus, pterygoid plexus and facial vein
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15
Q

State the nerves which innervate the orbit

A
  • General sensory from the eye through ophthalmic division of trigeminal nerve
  • Special sensory vision from retina through optic nerve
  • Motor nerves to muscle through occulomotor, trochlear and abducens
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16
Q

Describe the layers of the eyeball

A
  • Outer - fibrous, tough sclera (white of eye) continuous anteriorly as transparent cornea
  • Middle - vascular consisting of choroid, ciliary body and iris
  • Inner - retina (inner photosensitive layer lying on an outer pigmented layer)
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17
Q

Describe the iris and lens

A
  • Iris is a muscle that can dilate and constrict under autonomic control to help focus
  • Lens are suspended by suspensory ligament to ciliary muscle
  • Under parasympathetic control where contraction of muscle reduces tension of ligament and causes lens to become fatter
18
Q

Outline how light is perceived in the retina

A
  • Light must reach the photosensitive retina to be detected by photoreceptors (rods and cones)
  • Action potentials generated in response to light
  • Pass via ganglion cells whose axons collect in area of optic disk to optic nerve
  • Rods are for vision in low intensity light
  • Cones are for vision in high intensity light and colour vision - concentrated in macula
19
Q

Describe refraction and where it occurs

A
  • Refraction is the change in direction of light on passing through boundary of two different mediums
  • Light will be refracted from air into liquid tear film
  • Cornea is where most light refraction occurs (air-cornea interface)
  • Refraction through lens and vitreous humour before reaches retina
20
Q

Explain the accommodation reflex

A
  • Focusing near objects requires greater refraction of light
  • Pupil constricts - increase focus so lens don’t have to refract as much light
  • Eyes converge - image is brought to focus on same point of retina in both eyes
  • Lens become more biconcave (fatter) - ciliary muscles contract
21
Q

Describe problems of lens

A
  • As we age, the lens become stiffer and less able to change shape
    • Presbyopia - age related inability to focus near objects
  • Progressive opacities can also occur within lens
    - Cataracts - non-transparent lens
22
Q

Explain what the macula and optic disk are

A
  • Macula - area of the retina upon which an object in your visual field falls if you gaze direct at it (center of vision)
  • Optic disk - accumulation of retinal axons that leave the eye as the optic nerve
    - No photoreceptors present (blind spot)
23
Q

Explain what is found on a retinal scan

A
  • Macula is a dark spot and optic disk is a light spot
  • Veins are thicker than arteries due to larger lumen
  • Optic disk always medial to macula (to tell which eye)
24
Q

Levator palpebrae superioris action, innervation, damage presentation

A
  • Action - elevates upper eyelid
  • Innervation - CN III
  • Damage - ptosis
25
Q

Palpebral part of orbicularis oculi action, innervation, damage presentation

A
  • Action - blink/close eyes
  • Nerve - temporal branch of CN VII
  • Damage - can’t close eyes properly
26
Q

Superior tarsal muscle action, innervation, damage presentation

A
  • Action - keeps upper eyelid elevated
  • Innervation - sympathetic
  • Damage - partial ptosis
27
Q

State the extra-ocular muscle actions and innervation

A
  • Lateral rectus
    • Action - abduction of eye
    • Innervation - CN VI
  • Medial rectus
    • Action - adduction of eye
    • Innervation - CN III
  • Superior rectus
    • Action - elevation, intorsion, adduction of eye
    • Innervation - CN III
  • Inferior rectus
    • Action - depression, extorsion, adduction of eye
    • Innervation - CN III
  • Inferior oblique
    • Action - elevation, extorsion, abduction of eye
    • Innervation - CN III
  • Superior oblique
    • Action - depression, intorsion, abduction of eye
    • Innervation - CN IV
  • LR6SO4
28
Q

State what extra-ocular muscles are involved in looking left/right, up and down

A
  • Looking left and right due to medial and lateral rectus muscles
  • Looking upwards due to superior rectus and inferior oblique muscles
  • Looking downwards due to inferior rectus and superior oblique
29
Q

How are lateral and medial rectus tested

A

Abduction and adduction of eye

30
Q

How are inferior rectus and superior oblique tested

A
  • Superior oblique - move eye into medial position (looking towards nose) then move eyeball down
  • Inferior rectus - move eye into lateral position then move eyeball down
31
Q

How are inferior oblique and superior rectus tested

A
  • Inferior oblique - move eye into medial position then move eyeball up
  • Superior rectus - move eye into lateral position then move eyeball up
32
Q

Describe the presentation of CN III damage

A
  • Eyeball in down and out position
    • CN III innervates all muscles except lateral rectus and superior oblique
  • Severe ptosis
    • CN III innervates levator palpebrae superioris
  • Pupil dilation
    - CN III carries parasympathetic function to sphincter pupillae
33
Q

Describe the presentation of CN IV

A
  • Eyeball is held extorted, and up and in
    • CN IV innervates superior oblique muscle
  • Compensate for the slight extortion of eyeball by tilting the head slightly
  • Difficulties when looking down and medially
34
Q

Describe the presentation of CN VI

A
  • Unopposed pull of medial rectus muscle
    - Innervates lateral rectus
  • Unable to abduct the eye on affected side
  • Diplopia
35
Q

Describe the route of aqueous humour in the eye

A
  • Aqueous humour secreted by ciliary processes within ciliary body
  • Flows from posterior chamber through pupil into anterior chamber
    • Anterior chamber - between cornea and iris
    • Posterior chamber - between iris and lens
  • Drains through iridocorneal angle - angle between iris and cornea
  • Trabecular meshwork helps Schlemm’s canal drain the aqueous humour into the venous circulation
36
Q

Describe the role of aqueous humour

A
  • Nourishes lens and cornea
  • Lens and cornea are avascular to allow light to pass through
  • Need aqueous humour to supply oxygen and nutrients
37
Q

Describe the type of glaucoma

A
  • Drainage of aqueous humour from anterior chamber can be blocked
    • Trabecular meshwork deteriorates - old age
      • Open angle glaucoma
      • Blockage within the trabecular meshwork
    • Narrowing of iridocorneal angle - acute
      • Close angle glaucoma
      • Access to travecular meshwork is blocked off
  • Rise in intra-ocular pressure and damage to optic nerve
    • Optic disk cupping
    • Visual field loss
  • Sight threatening
  • Treatment - topical medications (eye droplets) that reduces production of aqueous humour or increase its drainage
38
Q

Explain the principal of colour blindness

A
  • Colour blindness - 3 types of cones (red, green, blue sensitive)
  • Absence or dysfunction of one of these three cones leads to colour blindness
39
Q

Describe papiloedema

A
  • Optic disk swelling due to increased intracranial pressure
  • Usually occurs in both eyes
  • Increased size of the blind spot means patients may lose vision briefly
40
Q

Describe blepharitis

A
  • Inflammation of the eyelids
  • Inflamed, irritated, itchy, and reddened eyelids
  • Can be due to bacterial infection, skin disease, blockage of Meibomian glands
41
Q

Outline the steps for a clinical examination of the eye

A
  • IVA FROM
  • Inspect - general, eyelids, conjunctiva, sclera
  • Visual Acuity
    • Snellen chart with one eye
    • 6/18 means that standing 6 meters away, the patient can only see the letter size that should be seen from 18 meters away in a person with normal vision
  • Visual Fields
    • Move hand slowly towards the centre and see where the patient first sees your finger
  • Reflexes - pupil light reflex, accommodation reflex
  • Ophthalmoscopy
    • Dim lights and sit opposite the patient and shine light
      • Pupil should appear pink/red (retina)
    • Slowly move the light towards the eye at an angle to observe the optic disk on the medial side
    • Follow blood vessels out from the optic disk and check macula
  • Movements of the eye
    - Keeping head still, follow fingers with your eye

3 - HNN (15 decks)

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