5) The orbit & the eye

Question 1

What are the boundaries of the orbit?

Answer 1

Roof - Frontal & Sphenoid bones
Floor - Maxilla, Zygomatic (& palatine)
Medial - Ethmoid, Maxilla, Lacrimal
Lateral - Zygomatic, Sphenoid

Question 2

Where do fractures of the orbit usually occur?

Answer 2

Bony sutures
Medial & inferior walls thin
Medial - Can involve Ethmoidal & Sphenoidal sinus
Inferior - Can involve Maxillary sinus

Question 3

What is a ‘blow out’ fracture?

Answer 3

Fracture that displaces the orbital walls & contents
Muscle entrapment
Diplopia
Infection

Question 4

Describe Enopthalmos

Answer 4

Depression of eye
opposite of exophthalmos
Infraorbital bleeding may push eyeball back out (pulsatile)

Question 5

What are the contents of the Superior Orbital Fissure?

Large French Teenagers…

Answer 5

Large French Teenagers Sit Numb In Anticipation Of Sweets (Lateral to Medial):
Lacrimal nerve
Frontal nerve
Trochlear nerve
Superior branch of oculomotor nerve
Nasociliary nerve
Inferior branch of oculomotor nerve
Abducens nerve
Ophthalmic veins
Sympathetic nerves

Question 6

Describe the optic nerve

Answer 6

Exits orbit via optic canal
Coverings of pia, arachnoid & dura maters of meninges
(continuous with brain, infection spread)
Central artery & vein

Raised ICP - venous engorgement, papilloedema (optic disc swelling)

Question 7

Name the 7 extraocular muscles of the orbit

Answer 7

4 Recti:
Superior, Inferior, Medial & Lateral
2 Obliques:
Superior & Inferior
& Levator Palpebrae superioris

Question 8

What is the innervation of the extraocular muscles of the orbit?
LR6SO4R3

Answer 8

Lateral Rectus - CN VI (Abducens)
Superior Oblique - CN IV (Trochlear)
all the Rest - CN III (oculomotor)

Question 9

What is an abducent nerve palsy?

Answer 9

Loss of innervation of Lateral Rectus
- Unable to abduct pupil (move laterally)
- Pupil fully adducted (unopposed medial rectus)
Caused by fractures of cavernous sinus/orbit

Question 10

What is a trochlear nerve palsy?

Answer 10

Loss of innervation to Superior Oblique
- Unable to look down when eye adducted
Caused by orbital fractures/stretching of nerve around brainstem

Question 11

What is an oculomotor nerve palsy?

Answer 11

Loss of innervation to ‘All the Rest’
- Ptosis (loss of LPS, unopposed orbicularis oculi)
- Fully dilated, non-reactive pupil (loss of sphincter pupillae, unopposed dilator pupillae)
- eye moved DOWN & OUT (unopposed LR & SO)
Caused by fractures involving cavernous sinus or aneurysms

Question 12

What is the blood supply to the eye?

Answer 12

Ophthalmic artery (branch of ICA)
Central artery of Retina (branch of ophthalmic)

End arteries - obstruction, instant & total blindness

Question 13

Describe the venous drainage of the eye

Answer 13

Superior & Inferior Ophthalmic veins drain into cavernous sinus
Central vein of Retina drain into cavernous sinus

Occlusion - slow, painless loss of vision
Infections may spread via this route from eye to brain

Question 14

What is the function of the eyelids?

Answer 14

Protect cornea & eyeball

Keep cornea moist - cover with lacrimal fluid via blinking

Question 15

What strengthens the eyelids?

Answer 15

Tarsal plates, dense bands of connective tissue containing Tarsal glands (lubricate edges of eyelids & prevent sticking)

Question 16

What 4 main things make up the lacrimal apparatus?

Answer 16

Lacrimal gland (secretes lacrimal fluid - tears)
Lacrimal ducts
Lacrimal canaliculi
Nasolacrimal duct

Question 17

Which muscles open the eyelids?

Answer 17

Levator palpebrae superioris (CN III)
+ Superior Tarsal muscles

(Horner’s Syndrome)

Question 18

Which muscles close the eyelid?

Answer 18

Orbicularis Oculi (CN VII)

Bell’s Palsy

Question 19

What happens if the eyelids are prevented from closing properly?

Answer 19

Protective blinking lost
Cornea becomes dry, unprotected from dust etc
Irritation of eyeball - excessive tear formation

Question 20

What are the 3 layers of the eyeball?

Answer 20

Outer protective layer
Middle vascular layer
Inner retina layer

Question 21

What makes up the outer protective layer of the eyeball?

Answer 21

Sclera

Cornea

Question 22

What makes up the middle vascular layer of the eyeball?

Answer 22

Choroid
Ciliary body
Iris

Question 23

What makes up the inner retina layer of the eyeball?

Answer 23

Optic part - photosensitive

Non-visual part

Question 24

What 3 things is the retina made up of?

Answer 24

Fundus
Macula
Optic Disc

Question 25

What is myopia?

Answer 25

Short or near-sight, "short-sightedness" Image focussed in front of retina (Long distance objects are out of focus)

Question 26

What is hyeropia/hypermetropia?

Answer 26

Long or far-sight, "long-sightedness" Image focussed behind the retina (Short distance objects are out of focus)

Question 27

What is presbyopia?

Answer 27

Far sight "long-sightedness" | Due to age-related changes of lens

Question 28

What is the purpose of aqueous humor?

Answer 28

Responsible for intraocular pressure Produced by ciliary process Drains into scleral venous sinus

Question 29

How is glaucoma caused?

Answer 29

Raised intraocular pressure Outflow of aqueous humor blocked Pressure builds up in anterior & posterior chambers of eye

Question 30

How does short-sightedness (myopia) occur?

Answer 30

Parasympathetic activity of CN III Sphincter like contraction of ciliary muscle Lens more globe like/fatter

Question 31

How does long-sightedness (hyeropia) occur?

Answer 31

No parasympathetic activity to ciliary muscles Lens stretched Flatter lens Becomes thicker with age (presbyopia)

Question 32

What are cataracts?

Answer 32

Clouding of the lens Decreases vision Reduced focusing power of lens

Question 33

Name some of the causes of cataracts

Answer 33

``` Age Trauma Radiation Genetics Skin diseases Drug use ```

Question 34

What is the purpose of vitreous humor?

Answer 34

Holds retina in place Retina: Rods - low light black & white Cones - Bright light, colour vision

Question 35

What is the corneal reflex testing?

Answer 35

Contraction of the orbicularis oculi causing the eye to blink Afferent fibres - Ophthalmic nerve (Vi) Efferent fibres - Temporal & zygomatic branches of facial nerve Loss of reflex - corneal ulceration

Question 36

What is mydriasis?

Answer 36

Dilation of the pupil - under activity of PSNS, lack of innervation to sphincter pupillae - over activity of SNS, increase innervation to dilator pupillae May be caused by raised ICP

Question 37

How is blindness related to glaucoma?

Answer 37

Compression of inner layer of eyeball (retina) & central artery of retina

Question 38

How may retinal detachment be caused?

Answer 38

Blow to eye (detachment may occur days or weeks after trauma) Pigment cell layer not firmly attached to neural layer Flashes of light or specks seen

Question 39

What is coloboma?

Answer 39

Absence of a section of the iris | Birth defect, penetrating or non-penetrating injuries to eyeball, surgical iridectomy

Question 40

What is hyphema?

Answer 40

Haemorrhage within the anterior chamber of the eyeball Usually blunt force trauma to eyeball Haemorrhages usually stops within few days

Question 41

What is exopthalmos?

Answer 41

Protrusion of the eye | whites of sclera visible all around cornea & iris

Question 42

What are the causes of exopthalmos?

Answer 42

Bilateral: Grave's disease (Hyperthyroidism) Unilateral: Aneurysm, haematoma

Question 43

What may be the consequences of raised intracranial pressure?

Answer 43

Compression of optic nerve & blood vessel supplying retina Blindness Vein occluded before artery, oedema of retina (papilloedema)

Question 44

What is a meibomian cyst?

Answer 44

Blocked tarsal gland | Lies behind eyelash within eyelid

Question 45

What is a stye?

Answer 45

Infection of the sebaceous gland at the base of the eyelash