Optic nerve sheath: measure 3 mm behind the globe

Question 1Where do you measure the optic nerve sheath diameter?

1. aAt the optic disc
2. b10 mm behind the globe
3. c3 mm behind the globe, outer edge to outer edge
4. dAcross the lens

Question 2A drowsy patient after a head injury has a sheath of 6.5 mm in both eyes. What next?

1. aRepeat the scan tomorrow before acting
2. bDiagnose a retinal detachment
3. cReassure: the finding is normal
4. dUrgent CT and senior review: the finding supports raised intracranial pressure

Question 3A patient with a severe headache has a normal sheath. What do you conclude?

1. aThe headache is benign
2. bNo CT is needed
3. cRaised intracranial pressure is not excluded
4. dRaised intracranial pressure is excluded

Question 4Why use the ophthalmic preset?

1. aIt removes the need for gel
2. bIt shows colour flow automatically
3. cIt makes the sheath look wider
4. dIt keeps the ultrasound power within the limits set for the eye

Question 5When must you not scan the eye?

1. aWhen the patient has a headache
2. bWhen the patient is drowsy
3. cWhen an open globe injury is suspected
4. dAfter a head injury