Anatomy Of Eye And Orbit

Question 1

What bones are the weakest within the orbit?

Answer 1

Ethmoid bone and maxilla due to air sinuses reducing the density of the bone. Maxilla commonly fractured in orbit trauma.

Question 2

How might an orbital blowout fracture present?

Answer 2

Entrapment of upward gaze, double vision, numbness of the cheek.

Question 3

Which nerve may be damaged in orbital blowout fracture, resulting in numbness of the cheek?

Answer 3

Infraorbital nerve (branch of Vb)

Question 4

What supplies blood to the retina?

Answer 4

Central retinal artery, running the through the centre of the optic nerves. Also supplied by ciliary arteries of the choroid layer that branch off of the opthalmic artery. The retina requires both blood supplies to function

Question 5

What veins drain the orbit and eye?

What do they connect with?

Answer 5

Superior and inferior Opthalmic veins - connect with cavernous sinus, pterygoid plexus and facial vein.

Question 6

What layers make up the eyelid?

Answer 6

Skin,
Subcutaneous tissue,
Muscle (orbicularis oculi),
Tarsal plate (firm connective tissue structure).

Question 7

Which glands of the eye lids are found within the tarsal plate?
What is their function?

Answer 7

Meibomian glands.

Modified sebaceous glands that provide a lipid later of tear film to prevent tear evaporation and spillage over the lid.

Question 8

What characterises a stye?

Answer 8

Found on outer margin of the lid,
Painful,
Infected (usuallly associated with staphylococcus species),
Pus.

Question 9

What characterises a meibomian cyst?

Answer 9

Found deeper within the lid,
Painless,
Caused by blockage of the duct,
Often resolve spontaneously.

Question 10

What is blepharitis?
What are common causes?
How is it treated?

Answer 10

Inflammation of the eye lid margin.
Caused by meibomian gland dysfunction or infection.
Treated with warm compresses and lid hygeine.

Question 11

What is the orbital septum?

Answer 11

Fibrous connective tissue layer continuous with the tarsal plate. Separates infraorbital contents from the muscle and tissue of the eyelid - important for preventing infection.

Question 12

How may periorbital (preseptal) cellulitis present differently to orbital (postseptal) cellulitis?

Answer 12

Periorbital is less serious and eye movements remain unaffected.
Orbital reduces visual acuity and eye movements, presenting with proptosis or exopthalmos.

Question 13

What complications may occur secondary to orbital cellulitis?

Answer 13

Cavernous sinus thrombosis, meningitis.

Question 14

What three layers comprise tear film?

Answer 14

Oily (sebaceous), water, mucus.

Question 15

Why does your nose run when you cry?

What is excessive tearing caused

Answer 15

The nasolacrimal duct and punctum drain tears into the nasal cavity, causing watery secretion from the nose. This duct can also block in certain pathologies causing - Epiphora.

Question 16

Why can’t you lose your contacts under your eye?

Answer 16

The conjunctiva sit anterior to the sclera and connect to the upper and lower lids.

Question 17

How does conjunctivitis typically present?

Answer 17

Watery eyes +- discharge,
Very infectious (often adenovirus),
Red conjunctiva of eye,
Gritty feeling.

Question 18

How do subconjunctival haemorrhages typically present?

Answer 18

Painless with no other symptoms. Happen spontaneously.

Question 19

What is the uveal tract?

What pathology occurs here?

Answer 19

Continuation of the choroid with the ciliary body and iris.

Uveitis.

Question 20

What is the macula?

What is the fovea?

Answer 20

Macula - point of highest visual acuity due to high density of cone cells.
Fovea - central pit of macula.

Question 21

How would central retinal artery occlusion present?

Answer 21

Sudden painless loss of sight in one eye. On fundoscopy - cherry red spot. This is sight threatening.

Question 22

What secretes aqueous humour?

Where does aqueous Humor drain from the eye?

Answer 22

Ciliary processes of the ciliary body.

Iridocorneal angle of the iris via the trabecular network into the canal of schlemm.

Question 23

What is glaucoma?

Answer 23

Optic nerve damage due to raised intraocular pressure. Often results due to damage of the structures that drain aqueous Humor of the eye.

Question 24

How does open angle glaucoma differ from closed angle glaucoma?

Answer 24

Open angle - due to deterioration of trabecular network with age. Chronic onset.
Closed angle - due to narrowing of iridocorneal angle. Acute onset and sight threatening

Question 25

What sign of glaucoma (or raised intraocular pressure) is seen on fundoscopy?

Answer 25

Glaucomatous cupping. Increased optic cup:disc ratio.

Question 26

What symptoms are associated with angle closure glaucoma?

Answer 26

Painful red eye,
Blurring of vision,
Oval shaped pupil,
Halos around lights,
Nausea and vomiting.

Question 27

Where does most light refraction happen in the eye?

Answer 27

Tear film lining the cornea. Also occurs at the lens.

Question 28

What happens during the accommodation reflex?

Answer 28

Pupil constricts,
Eyes converge,
Lens becomes more biconvex (fatter).
Lens stiffens with age.

Question 29

What is presbyopia?

Answer 29

Age related inability to focus near objects due to stiffened shape of the lens.

Question 30

Where is the blind spot?

Answer 30

Optic disc - no photoreceptors found here as it is the origin of the optic nerve.

Question 31

How is visual acuity measured?

What is normal visual acuity?

Answer 31

Snellen chart: stand 6m away covering one eye at a time and read letters.
6/6 considered normal.

Question 32

What may cause decreased visual acuity?

Answer 32

Cataracts,
Astigmatism,
Presbyopia,
Macular degeneration,
Optic neuritis.

Question 33

Why does the red reflex occur?

When might it be absent?

Answer 33

Highly vascular retina and choroid reflect red light.

Cataracts or malignancy (retinoblastoma).

Question 34

How can visual acuity be categorised into a refractive or non refractive cause?

Answer 34

Refractive cause would improve upon use of a pinhole test, as it focuses light onto the lens. It would have no effect if visual acuity was from a non refractive cause.