The Orbit and Eye - 3

Question 1

What do branches of the opthalmic artery supply?

Answer 1

They supply mucous membrane of the ethmoidal air sinuses and the root of the nose.

Question 2

What do the anterior and posterior ethmoidal arteries accompany through the medial wall of the orbital cavity?

Answer 2

They accompany branches of the nasociliary nerve through foramina which are named after the arteries, out through the medial wall of the orbital cavity.

Question 3

What is the most important branch of the ophthalmic artery?

Answer 3

The most important branch is the central artery of the retina.

Question 4

What nerve does the central artery of the retina travel in?

Answer 4

It travels in the optic nerve.

Question 5

What is the significance of the central artery of the retina?

Answer 5

This is the only artery to the retina and blockage of this artery causes complete blindness.

Question 6

Where do veins that drain the orbital cavity drain into?

Answer 6

These veins drain into the cavernous sinus.

Question 7

Where do many veins from the forehead and the face drain?

Answer 7

They drain back into the orbital cavity and so they drain into the cavernous sinus.

Question 8

What is the significance of having no valves in the veins that drain the orbital cavity and the forehead and the face?

Answer 8

Because there are no valves, the direction of blood flow can reverse.

Question 9

What bone do fractured orbits involved?

Answer 9

Fractured orbits are common and they often involve the zygomatic bone.

Question 10

What is a symptom of a fractured orbit?

Answer 10

The patient complains of seeing double = diplopia.

Question 11

Why do fractured orbits cause diplopia?

Answer 11

This could either be the suspensory ligament which supports the eye in the horizontal plane is no longer fixed in position or because the fractured bone now directly obstructs movements of the rectus muscles.

Medial and inferior walls of the orbit are very thin and a blow to the eye that compresses the contents of the orbital cavity (a hard ball striking the eyeball and orbital margin) is in danger of producing a blow out fracture of the orbital cavity.

Question 12

Where do foregin bodies ‘in the eye’ often lodge?

Answer 12

They often lodge under the upper eyelid in the superior fornix.

Question 13

What can happen if a foreign object injures the cornea?

Answer 13

It can cause corneal abrasion.

Question 14

What are infections of the conjunctiva called?

Answer 14

They are called conjunctivitis.

Conjunctivitis can ulcerate the cornea.

Question 15

When are deeper infections of the conjunctiva more serious?

Answer 15

They are more serious when the iris and ciliary body are involved. These are called iridocyclitis.

Question 16

What is a cataract?

Answer 16

This is when there is opacity developing in the lens.

When lens becomes completely opaque it may be removed surgically to restore vision.

Question 17

What is squint or strabismus?

Answer 17

This is a deviation of the eyes so that their axes are no longer parallel to each other - this excludes normal convergence that occurs when the eyes adapt to very close work.

Question 18

What can a squint be caused by?

Answer 18

It can be caused by a lesion of one of the cranial nerves that supply the extraocular muscles or it may because of a localised problem to one of the muscles.

Question 19

What direction can a squint be in?

Answer 19

A squint may be in any direction but it is mostly horizontally

When the eyes tend to look towards each other the squint is said to be convergent and when they look away from each other the squint is said to be divergent.

Question 20

What does the oculomotor nerve supply?

Answer 20

• supplies voluntary part of levator palpebrae superioris
• all the other extraocular muscles except superior oblique and lateral rectus
• carries parasympathetic fibres which constrict the pupil and act on the ciliary muscles during the accomodation reflex

Question 21

What happens when there is an oculomotor nerve lesion?

Answer 21

• There is unopposed sympathetic activity on the dilator pupillae muscle therefore the pupil will remain dilated.
• Accomodation to close vision is impossible.
• Upper eyelid closes because the involuntary portion of the levator palpebrae superioris is unable to raise the eyelids on its own
• Unopposed action of the lateral rectus muscle which abducts the eye
  
  • in this position the superior oblique muscle is aligned across the equator of the eye and it can only rotate or intort the globe.

Many oculomotor nerve lesions are only partial and therefore they are more difficult to spot than a complete 3rd nerve lesion.

Question 22

What happens when there is a lesion of the 6th cranial nerve?

Answer 22

The patient is unable to abduct the eye to the side of the lesion.

If the patient tries to abduct the eye to the side of the lesion, this leads to double vision because the unaffected eye abducts and the affected eye remains centrally placed.

Question 23

Describe lesions of the 4th cranial nerve.

Answer 23

These are extremely rare on their own.

They are usually picked up because the patient is unable look down towards the nose and this leads to difficulty walking down the stairs.

When the eye is medially placed the superior oblique muscle is aligned along its visual axis and therefore becuase it is inserted behind the equator of the globe, it is perfectly positioned to depress the eyeball. This is not possible in a 4th cranial nerve lesion.

Question 24

What does Horner’s syndrome result from?

Answer 24

It results when there is disruption of the sympathetic trunk.

Question 25

What can cause disruption of the sympathetic trunk?

Answer 25

• This can be caused by a lung tumour invading the trunk either in the thorax or the neck.
• Can be a result of a poorly placed local anaesthetic in the neck or mouth.

Question 26

What happens when there is a disruption of sympathetic trunk?

Answer 26

• There is unopposed paraysmpathetic activity which results in a constricted pupil and a hot flushed dry face and neck since it is sympathetic fibres that innervate sweat glands and are vasoconstrictor in action.
• drooping of the upper eyelid because of the loss of sympathetic innervation to levator palpebrae superioris
  
  • voluntary fibres to the levator palpebrae superioris from the ocular motor nerves are insufficient on their own to raise the lid completely.