Using a penlight, test the ipsilateral and consensual pupillary light reflex

Question 1

Describe and demonstrate how to test the ipsilateral and consensual pupillary reflexes

Answer 1

• Inform the patient what you’re going to do
• Shine the light in the eye and check for pupil shrinking (miosis)
• Wait 3 seconds
• Repeat and this time check for miosis occuring in the other eye despite shining in that eye

Question 2

1) Describe the neurological circuitry going on involved in the pupillary light reflexes and thereby explain how it causes ipsilateral and consensual light reflexes
2) Where is the lesion if you don’t get a response in either eye at all, and where is the lesion if you failed to get a consensual response but you get an ipsilateral response

Answer 2

1)
Light goes in through optic nerve, this goes to the pretectal nucleus and then through the edinger-westphal nucleus which are both ipsilateral and consensual (so sort of like a branching point after the pretectal nucleus).
• Then this goes via parasympathetic ocul•omotor nerve fibres to the ciliary ganglion which eventually goes to the ciliary muscle and controls the contraction in both eyes

2)
• If you have no response whatsoever, the lesion is most likely in the optic nerve
• If you have a preserved ipsilateral but absent consensual light reflex, the lesion is either at the edinger-westphal nucleus or the parasympathetic oculomotor nerve fibres on the side with the absent reflex