PUPIL PATHWAYS

Question 1

The pupil light reflex afferent pathway begins at which of the following structures?

Answer 1

Retinal ganglion cells

Question 2

The pupil light reflex efferent pathway begins at which of the following structures?

Answer 2

Edinger Westphal nucleus

Question 3

CLINICAL CONSIDERATIONS

Lesion #1: Total damage to right optic nerve (blind right eye = NLP)

Answer 3

Shine light in right eye:
Is there direct pupil constriction? No
Is there consensual pupil constriction? No
The pupil stays the same size because light (information on light perception) cannot get through (doesn’t matter if it crosses or not)

Shine light in left eye
Direct pupil constriction? Yes
Consensual pupil constriction? Yes
(nasal fibers will cross; nasal fibers will get to contralateral pretectal going to both EW and come back)

Question 4

Lesion #2: PARTIAL damage to right optic nerve

Answer 4

Shine light in LEFT EYE:
What does the left pupil do? constrict
What does the right pupil do? constrict

Quickly swing light to RIGHT EYE.
What does the right pupil do? dilate a bit (compared to when it was in the left eye)
What does the left pupil do? dilate a bit
Why? information sent back is not as strong (not a full dilation though)

Quickly swing light to LEFT EYE.
What does the left pupil do? constrict
What does the right pupil do? constrict
Why?

Question 5

Lesion #3: Split the optic chiasm.

Answer 5

Shine light in right eye.
Is there direct pupil constriction? yes
Is there consensual pupil constriction? yes
Why? temporal fibers go back and activate both pretectal nuclei

Shine light in left eye.
Direct pupil constriction? yes
Consensual pupil constriction? yes
Why? temporal fibers activate pretectal nuclei which activate both EW nuclei

Question 6

Lesion #4: Total damage to right optic tract

Answer 6

Shine light in right eye:
Is there direct pupil constriction? yes
Is there consensual pupil constriction? yes
nasal fibers cross

Shine light in left eye:
Direct pupil constriction? yes
Consensual pupil constriction? yes
both EW nuclei still activated

Question 7

Lesion #5: Damage to the left oculomotor nerve (CN3)

Answer 7

Shine light in right eye:
Is there direct pupil constriction? yes
Is there consensual pupil constriction? no
efferent pathway is damaged

Shine light in left eye:
Direct pupil constriction? no
Consensual pupil constriction? yes
afferent fibers went to both EW nuclei

Question 8

Which 2 of the following nuclei are involved in the convergence component of the near triad?

Answer 8

Oculomotor nucleus, Abducens nucleus

Question 9

Which 2 of the following statements, when combined, best describes a light-near dissociation?

Answer 9

Pupils constrict when viewing a near target

Pupils do not constrict with light