Week 6 - The Orbit, Extraocular Muscles and The Eye Flashcards
Outline the direct and consensual light reflexes. (direct is the left, in this case)
- Light in left pupil
- Sensory afferent in left retina - CN II
- To brainstem - pretectal nucleus
- Connection with EDW nuclei - left and right
- Parasympathetic fibres from EDW leave brainstem
- Hitch-hike on CN III - left and right
- Pass via ciliary ganglion
- Reach sphincter pupillae
- Direct - left, consensual - right
Why is the cornea not affected in conjunctivitis?
Because the conjunctivae ends at the limbus, hence the cornea is not affected because the conjunctivae does not overlie the cornea
What is a Meibomian cyst (chalazion) due to?
A blocked tarsal (meibomian gland) which lie posterior to the eyelash, within the tarsal plates (eyelids)
What is a stye (external hordeolum) due to?
Infection of a sebaceous gland situated at the base of the eyelash (lash follicle)
Why can’t the eye be elevated in an orbital blow-out fracture?
Due to trapping of the inferior rectus muscle, which prevents the eye being elevated by the other extra-ocular muscles
Why is there reduced sensation over the cheek in an orbital blow-out fracture?
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
Why might suturing a wound caused by an orbital blow-out fracture not be so straightforward?
- 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
Superior rectus:
- Cranial nerve supply
- Clinical movement tested
- III
2. Move eye up and out
Inferior rectus:
- Cranial nerve supply
- Clinical movement tested
- III
2. Moves eye down and out
Superior oblique:
- Cranial nerve supply
- Clinical movement tested
- IV
2. Moves eye down and in
Inferior oblique:
- Cranial nerve supply
- Clinical movement tested
- III
2. Moves eye up and in