Question

A new mother brings in her 6‐month‐old baby for not being able to keep his eyes together when

looking to the left. On examination, both of his eyes appear in alignment (conjugate) when
looking to the right. However, when looking to the left, the baby's left eye stays in the forward
gaze position, while the right continues on with full adduction to the left. The eyes appear to be
out of alignment (dysconjugate). Which cranial nerve (CN) is responsible for the dysfunction in
looking left?

) The left oculomotor nerve (CN III)
b) The right abducens nerve (CN VI)
c) The right trochlear nerve (CN IV)
d) The right oculomotor nerve (CN III)
e) The left trochlear nerve (CN IV)
f) The left abducens nerve (CN VI)

Answer 1

Answer: f) The left abducens nerve (CN VI)

Step-by-step explanation:

The correct response is the left abducens nerve (CN VI), since the left abducens nerve (CN VI) pushes the left eye outwards towards the left. The muscle's paresis or weakness can create the baby's inability to move the left eye outwards to the left.

The right oculomotor nerve (CN III) is wrong as this nerve pushes the right eye upwards, upwards and inwards, upwards and outwards, downwards and outwards.

The right trochlear nerve (CN IV) is wrong as this nerve travels downwards and inwards the right eye.

The right nerve abducens (CN VI) is incorrect as this nerve pushes the right eye outwards to the right.

The left oculomotor nerve (CN III) is wrong as this nerve pushes the left eye inwards, upwards and inwards, upwards and outwards and downwards and outwards.

The left trochlear nerve (CN IV) is incorrect, as this nerve pushes the left eye downwards and inwards.

Hence, the correct option is f) The left abducens nerve (CN VI).