The Orbit and the Eye

Question 1

describe the general structure of the bony orbit?

Answer 1

pyramidal structure

Question 2

what forms the peak at the top of the pyramid?

Answer 2

optic canal (at the back in the middle)

Question 3

what forms the roof of the bony orbit?

Answer 3

frontal bone

Question 4

what forms the medial wall of the bony orbit?

Answer 4

ethmoid
frontal
lacrimal
maxilla
components of each

Question 5

what forms the floor of the bony orbit?

Answer 5

mainly maxilla

Question 6

what forms the lateral wall of the bony orbit?

Answer 6

zygomatic

sphenoid

Question 7

which walls of the bony orbit are most likely to fracture and why

Answer 7

medial and inferior walls

very thin

Question 8

what structures are in place to protect the eye when subjected to a direct blow?

Answer 8

eyes are deep set
frontal, zygomatic, nasal bones etc all sit further out than the eye
orbital rim is thick and strong to resist fracture

Question 9

what is an orbital blow out and what can happen with this?

Answer 9

direct blow to the eye in between the bones of the orbit
increases the pressure in the eye
this increased pressure can cause walls to fracture and the contents of the eye to protrude through
can cause damage to nerves (e.g infraorbital NVB)

Question 10

how can an orbital blowout cause sensory deficit in the face?

Answer 10

infraorbital NVB passes through the infraorbital foramen and then out through the maxilla to provide sensory innervation to the face
blowout fracture damaging the orbital floor can therefore cause sensory damage in the face

Question 11

what are the 4 components of the eyelid?

Answer 11

outer skin
inner conjunctiva
eyelashes
glands

Question 12

what is contained within the eyelids?

Answer 12

tarsal plate
orbicularis oculi
levator palpebrae superioris

Question 13

what does the tarsal plate do?

Answer 13

maintains shape

contains meibomian glands which secrete lipids

Question 14

which nerve innervates the orbicularis oculi muscle in the eyelid?

Answer 14

CN VII (facial nerve)

Question 15

what does the levator palpebrae superioris do and which nerve innervates it?

Answer 15

opens the upper eyelid

innervated by CN III

Question 16

what can cause ptosis and why?

Answer 16

CN III palsy as CN III innervated levator palpebrae superioris

Question 17

what does the orbicularis oculi muscle do?

Answer 17

surrounds the eye

contraction closes the eye

Question 18

describe the surface anatomy of the eye

Answer 18

white sclera (covered by conjunctiva)
iris (covered by cornea)
- sclera and cornea are continuous and iris sits deep to these
limbus = corneoscleral junction (junction between cornea and sclera)
lacrimal glands in the upper lateral quadrant

Question 19

what is conjunctiva?

Answer 19

defensive barrier to small foreign objects (dust, insects etc)

Question 20

describe the lacrimal apparatus/pathway and how crying is connected to the nasal cavity?

Answer 20

lacrimal gland produces tears (supplied by CN VII - parasympathetic supply)
blinking washes these tears across to the medial angle of the eye
tears drain through tiny lacrimal puncta in the medial angle
tears drain into the canaliculi and then into the lacrimal sac
tears then pass into the nasolacrimal duct which connects the nasal cavity with the eye
tears reach inferior meatus of the nasal cavity

Question 21

what are the 3 layers of the eyeball?

Answer 21

fibrous outer layer
uvea (vascular) middle layer
retina (photosensitive) inner layer

Question 22

what are the 2 parts of the fibrous outer layer of the eyeball?

Answer 22

sclera = white, fibrous
cornea = for refraction of light

Question 23

what are the 3 parts of the uvea?

Answer 23

iris
ciliary body
choroid = nutrition and gas exchange

Question 24

what does the ciliary body in the uvea do?

Answer 24

controls iris, shape of lens and secretion of aqueous humour

Question 25

what are the parts of the retina?

Answer 25

macula optic disc cones and rods neural tissue

Question 26

what is the anterior segment of the eye and what are the 2 chambers contained within it?

Answer 26

anterior segment = in front of lens anterior chamber = between cornea and iris, contains aqueous humour posterior chamber = between iris and suspensory ligaments, contains aqueous humour

Question 27

what is the posterior segment and what is contained within it?

Answer 27

behind lens makes up 2/3rds of the eye contains vitreous body

Question 28

what is vitreous body?

Answer 28

mixture of vitreous humour | common site of floaters in the eye

Question 29

aqueous humour vs vitreous humour?

Answer 29

aqueous humour is continuously produced | vitreous humour present at birth and not replaced, thick and gelatinous and holds retina up against the eyeball

Question 30

what can too much aqueous humour cause?

Answer 30

increased pressure in the eye leading to glaucoma

Question 31

describe the path of circulation of aqueous fluid

Answer 31

ciliary processes in ciliary body produce aqueous fluid aqueous fluid circulates within the posterior chamber and nourishes the lens aqueous then passes through the pupil into the anterior chamber and nourishes the cornea aqueous fluid is then reabsorbed into the scleral venous sinus (canal of schlemm) at the iridocorneal angle

Question 32

what is the iridocorneal angle?

Answer 32

the angle formed by the iris and the cornea to allow drainage of aqueous humour the "angle" in "open angle" and "closed angle" glaucoma

Question 33

what can blockage of the canal of schlemm cause?

Answer 33

can increase pressure and cause ischaemia of the retina and glaucoma

Question 34

what is the arterial supply to the eye?

Answer 34

ophthalmic artery (branch of internal carotid) passes through the optic canal with the optic nerve central artery of the retina then branches off the ophthalmic artery and travels in the middle of the optic nerve (end artery) - central vein of retina also in middle of optic nerve

Question 35

describe venous drainage of the orbit

Answer 35

superior ophthalmic vein above the eye inferior ophthalmic vein blow the eye anastomosis forms where superior and inferior ophthalmic veins can drain anteriorly into the facial vein or posteriorly the two veins can join to form the cavernous sinus via the superior orbital fissure

Question 36

what is the danger triangle in the face and why is this the case?

Answer 36

upper lip and nose | area where infection is very dangerous as the venous drainage can drain the infection into the cavernous sinus

Question 37

what are the 4 components of the retina?

Answer 37

fundus (fundoscopy) which contains: - optic disc - macula - fovea

Question 38

what is the optic disc?

Answer 38

point of CN II formation only point of entry/exit for blood vessels and axons of CN II blind spot

Question 39

what is the macula?

Answer 39

greatest density of cones | good for colour vision

Question 40

what is the fovea?

Answer 40

centre of the macula 1.5 mm depression area of most acute vision

Question 41

what are the 3 layers of the retina from outermost to innermost?

Answer 41

1. axons of ganglion cells 2. ganglion cells 3. photoreceptor cells

Question 42

why is the optic disc known as the blind spot?

Answer 42

there are no photoreceptors

Question 43

what can complete interruption of flow in a retinal artery branch/retinal vein cause?

Answer 43

loss of an area of visual field corresponding to the area of ischaemia

Question 44

what can complete interruption of flow in the central artery or vein cause?

Answer 44

monocular blindness

Question 45

nerve fibres from where cross over in the optic chiasm?

Answer 45

nasal retina

Question 46

what are the extra-ocular muscles of the eye?

Answer 46

``` 4 straight muscles (rectus muscles) - superior rectus = to look up, up and in - inferior rectus = to look down, down and in medial rectus = eye adduction (medial) lateral rectus = eye abduction (lateral) oblique muscles (keep eye steady when head is moving) - superior oblique = rotates eye medially in the orbit, down and out - inferior oblique = rotates eye laterally in orbit, up and out ```

Question 47

what nerves innervate the extra-orbital muscles?

Answer 47

LR6 SO4 AO3 - lateral rectus = CN6 (abducens) - superior oblique = CN 4 (trochlear nerve) - All others = CN 3

Question 48

what does the superior oblique pass through before turning back on itself?

Answer 48

trochlear