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
2
Q
What are the openings at the apex of the orbital cavity
A
- Superior orbital fissure
- Inferior orbital fissure
- Optic canal
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
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
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
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
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
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
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
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
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
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
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
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
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
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)
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
Palpebral part of orbicularis oculi action, innervation, damage presentation
- Action - blink/close eyes
- Nerve - temporal branch of CN VII
- Damage - can't close eyes properly
26
Superior tarsal muscle action, innervation, damage presentation
- Action - keeps upper eyelid elevated
- Innervation - sympathetic
- Damage - partial ptosis
27
State the extra-ocular muscle actions and innervation
- 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
State what extra-ocular muscles are involved in looking left/right, up and down
- 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
How are lateral and medial rectus tested
Abduction and adduction of eye
30
How are inferior rectus and superior oblique tested
- 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
How are inferior oblique and superior rectus tested
- Inferior oblique - move eye into medial position then move eyeball up
- Superior rectus - move eye into lateral position then move eyeball up
32
Describe the presentation of CN III damage
- 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
Describe the presentation of CN IV
- 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
Describe the presentation of CN VI
- Unopposed pull of medial rectus muscle
- Innervates lateral rectus
- Unable to abduct the eye on affected side
- Diplopia
35
Describe the route of aqueous humour in the eye
- 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
Describe the role of aqueous humour
- Nourishes lens and cornea
- Lens and cornea are avascular to allow light to pass through
- Need aqueous humour to supply oxygen and nutrients
37
Describe the type of glaucoma
- 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
Explain the principal of colour blindness
- Colour blindness - 3 types of cones (red, green, blue sensitive)
- Absence or dysfunction of one of these three cones leads to colour blindness
39
Describe papiloedema
- 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
Describe blepharitis
- Inflammation of the eyelids
- Inflamed, irritated, itchy, and reddened eyelids
- Can be due to bacterial infection, skin disease, blockage of Meibomian glands
41
Outline the steps for a clinical examination of the eye
- 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
