12. Functional Anatomy And Disorders Of The Eye

Question 1

What 3 openings are found at the apex of the orbital cavity?

Answer 1

Superior orbital fissure.
Inferior orbital fissure.
Optic canal.

Question 2

What anatomical relation means the inferior and medial walls of the orbital cavity are weaker and also means infection can spread here?

Answer 2

Ethmoid sinuses found medially, and maxillary sinus found inferiorly.

Question 3

What causes an orbital blow out fracture?

Answer 3

Sudden increase in intra-orbital pressure, such as from retropulsion of the eye ball by fist or ball, fractures the floor of the orbit.

Question 4

Where can the orbital contents and blood prolapse into in an orbital blow out fracture?

Answer 4

The maxillary sinus.

Question 5

Why might someone with a blo out fracture be unable to look up?

Answer 5

Fracture site can trap structures, in this case the extra orbital muscle located near the floor or orbit.

Question 6

Why may a patient with an orbital blow out fracture experience anaesthesia over the affected check on the affected side?

Answer 6

Infraorbital branch of the maxillary division of the trigeminal nerve runs through the base of the eye, and so is damaged, leading to reduced sensation in upper teeth and gums.

Question 7

What sign is seen on a X-ray if tissue has prolapsed into the maxillary sinus in an orbital blow out fracture?

Answer 7

Tear drop sign.

Question 8

What does the orbital cavity contain?

Answer 8

Lacrimal apparatus.
Nerves and blood vessels.
Orbital fat.
Globe of the eye and its internal structures.
Extra-ocular muscles.

Question 9

What is the function of the tarsal plates of the eyelids?

Answer 9

Provide a connective tissue skeleton to the eyelid for firmness and shape.

Question 10

What is the orbital septum?

Answer 10

A thin sheet of fibrous tissue originating from the orbital rim which blends with the tendon of levator palpebrae superioris and tarsal plates.

Question 11

What structures does the orbital septum separate? What advantages does this provide?

Answer 11

Intra-orbital contents from eyelid fat and orbicularis oculi muscle.
Acts as a barrier against infection spreading from the pre-septal space to post-septal (orbital cavity proper).

Question 12

Name 2 causes of periorbital cellulitis

Answer 12

Secondary to infection from bites, periorbital trauma, sinuses (fronto-ethmoidal).

Question 13

How would you tell if a periorbital cellulitis is pre-septal or post-septal?

Answer 13

Pre-septal - swelling is localised.

Post-septal - swelling more diffuse.

Question 14

Give 2 complications of periorbital cellulitis

Answer 14

Abscess formation.
Spread of infection intracranially via veins of orbit draining to cavernous sinus, pterygoid venous plexus and facial veins, leading to a cavernous sinus thrombosis.

Question 15

What is the role of Meibomian glands?

Answer 15

Glands inside tarsal plates - secrete oily substance onto edge of eyelashes, when blink rubs over front of eye and stops tears from evaporating and dripping over the edge of the eyelid.

Question 16

What is a Meibomian cyst?

Answer 16

Blockage of the Meibomian glands by the oily substance they secrete, causing a painless cyst.

Question 17

What is a stye?

Answer 17

Glands of Zeis blocked due to staph infection, causing a painful lump.

Question 18

What is blepharitis?

Answer 18

Inflammation of the whole base of the lashes. Can affect the Meibomian glands.

Question 19

What is conjunctivae?

Answer 19

Transparent secretory mucosa producing mucous and tears lubricating the conjunctival and corneal surfaces of the eye. Highly vascular with small blood vessels within the membrane. Lacrimal apparatus also involved in secretion of tears into the conjunctival sac.

Question 20

What 3 structures make up the lacrimal apparatus?

Answer 20

Lacrimal gland.
Lacrimal sac.
Nasolacrimal duct.

Question 21

What is the function of blinking?

Answer 21

Washes tear film across the front of the eye, rinsing and lubricating the conjunctivae and cornea.

Question 22

What parts of the eye does the conjunctiva cover?

Answer 22

Sclera, inside of eyelids (forming a conjunctival sac), does not cover cornea.

Question 23

What is conjunctivitis?

Answer 23

Inflammed and infected conjunctiva.

Question 24

What is a subconjunctival haemorrhage?

Answer 24

Haemorrhage from a blood vessel in the conjunctiva.

Question 25

What is the main arterial supply of the orbit?

Answer 25

Ophthalmic artery and its branches.

Question 26

What nerves provide general sensory innervate to the eye, including the conjunctiva and cornea?

Answer 26

Ophthamic division of the trigeminal (Va).

Question 27

What nerve provides special sensory vision from the retina?

Answer 27

Optic nerve (CN III).

Question 28

What motor nerves innervate the muscles of the orbit?

Answer 28

Occulamotor (CN III), trochlear (CN IV), abducens (CN VI).

Question 29

What 3 things maintain the eyeball in position?

Answer 29

Suspensory ligament.
Rectus muscles.
Orbital fat.

Question 30

What are the three layers of the eyeball and what is each made up of?

Answer 30

Outer - fibrous, though sclera which is continuous anteriorly as the transparent cornea.
Middle - vascular consisting of the choroid, ciliary body and iris.
Inner - retina (an inner photosensitive layer lying on an outer pigmented layer nearest choroid).

Question 31

Where is aqueous humour of the eye produced?

Answer 31

Secreted by ciliary processes within the ciliary body of the eye.

Question 32

How does aqueous humour of the eye drain?

Answer 32

Flows from the posterior chamber, into the anterior chamber and drains through the iridocorneal angle via the trabecular mesh work into the canal of Schlemm.

Question 33

What is the purpose of aqueous humour in they eye?

Answer 33

Nourishes the lens and cornea as it is avascular.

Question 34

What is the canal of Schlemm?

Answer 34

Circumferential venous channel draining into the venous circulation.

Question 35

Give 2 causes of glaucoma.

Answer 35

Drainage of aqueous humour from the anterior chamber blocked either by deterioration of the trabecular meshwork (chronic eg age) or narrowing of the iridocorneal angle (acute).
Rise in intra-ocular pressure and damage to the optic nerve.

Question 36

What is glaucoma as a result of a deteriorated trabecular meshwork know as?

Answer 36

Open angle glaucoma.

Question 37

What is glaucoma as a result of narrowing of the iridocorneal angle known as?

Answer 37

Closed angle glaucoma.

Question 38

Describe the route of light to the optic nerve?

Answer 38

Photons reach photosensitive retina, detected by photoreceptors (rods and cones), action potentials generated in response to light, pass via ganglion cells whose axons collect in the area of optic disc to the optic nerve.

Question 39

At what three points is light refracted as it passes into the eye?

Answer 39

From air into liquid tear film.
Through cornea.
Through lends and vitreous humour before reaches retina.

Question 40

In distance refraction, where is light mainly refracted?

Answer 40

As light passes through the cornea.

Question 41

What reflex changes where light is refracted when looking at an object close up? What does this involve?

Answer 41

Accommodation reflex:

Pupil constricts, eyes converge, lens becomes more biconcave.

Question 42

In close refraction, where is light mainly refracted?

Answer 42

As light passes through cornea and lens.

Question 43

What is presbyopia?

Answer 43

Age related inability to focus on near objects, due to the lens becoming stiffer and less able to change shape with age.

Question 44

What are cataracts?

Answer 44

Progressive opacities within the lens occurring with age.