Week 6 - The Orbit, Extraocular Muscles and The Eye

Question 1

Outline the direct and consensual light reflexes. (direct is the left, in this case)

Answer 1

1. Light in left pupil
2. Sensory afferent in left retina - CN II
3. To brainstem - pretectal nucleus
4. Connection with EDW nuclei - left and right
5. Parasympathetic fibres from EDW leave brainstem
6. Hitch-hike on CN III - left and right
7. Pass via ciliary ganglion
8. Reach sphincter pupillae
9. Direct - left, consensual - right

Question 2

Why is the cornea not affected in conjunctivitis?

Answer 2

Because the conjunctivae ends at the limbus, hence the cornea is not affected because the conjunctivae does not overlie the cornea

Question 3

What is a Meibomian cyst (chalazion) due to?

Answer 3

A blocked tarsal (meibomian gland) which lie posterior to the eyelash, within the tarsal plates (eyelids)

Question 4

What is a stye (external hordeolum) due to?

Answer 4

Infection of a sebaceous gland situated at the base of the eyelash (lash follicle)

Question 5

Why can’t the eye be elevated in an orbital blow-out fracture?

Answer 5

Due to trapping of the inferior rectus muscle, which prevents the eye being elevated by the other extra-ocular muscles

Question 6

Why is there reduced sensation over the cheek in an orbital blow-out fracture?

Answer 6

Due to damage of the inferior (or infra-orbital) branch of the trigeminal nerve, maxillary branch V2 which emerges just below the orbit through the infra-orbital foramen

Question 7

Why might suturing a wound caused by an orbital blow-out fracture not be so straightforward?

Answer 7

• Injury to the area of the face near the medial angle of the eye may involve injury to the lacrimal canaliculi and nasolacrimal duct
• If such a wound is repaired without consideration to the lacrimal drainage system immediately beneath, the injured ducts can become stenosed as they heal
• The patient could be left with long-term problems due to excessive tearing and recurrent conjunctivitis due to impedance of tear drainage from that eye
• Wounds involving this area should be referred to a specialist, and treatment may involving microsurgery and placing a stent through the canaliculi/duct to ensure it remains patent as the wound heals

Question 8

Superior rectus:

1. Cranial nerve supply
2. Clinical movement tested

Answer 8

1. III

2. Move eye up and out

Question 9

Inferior rectus:

1. Cranial nerve supply
2. Clinical movement tested

Answer 9

1. III

2. Moves eye down and out

Question 10

Superior oblique:

1. Cranial nerve supply
2. Clinical movement tested

Answer 10

1. IV

2. Moves eye down and in

Question 11

Inferior oblique:

1. Cranial nerve supply
2. Clinical movement tested

Answer 11

1. III

2. Moves eye up and in