<s>[INST] context: When light is shone to one (e.g. left) eye, left optic nerve carries afferent impulse to brain and from brain efferent impulse to ipsiplateral (left) eye comes through ipsilateral (left) occulomotor nerve (for direct light reflex) and efferent for contralatcral (right) eye comes through contralateral (right) occulmotor nerve for consensual light reflex. When light is shone to other (right) eye, right optic nerve carries afferent impulse to brain and from brain, efferent impulse to right eye (for direct light reflex) comes through right occulmotor nerve and efferent for left eye (for consensual light reflex) comes through left occulomotor nerve. So :-


Optic nerve is responsible for direct light reflex in ipsilateral eye and consensual light reflex for contralateral eye. (In above example, afferent for right sided direct and left sided.consensual light reflex is through right optic nerve; and afferent for left sided direct and right sided consensual light reflex is through left optic nerve).
Occulomotor nerve is responsible for direct and consensual light reflex in the same eye. (In above example, efferent for right sided direct as well as consensual light reflex is through right occulmotor nerve and efferent for left sided direct as well as consensual light reflex is through left occulomotor nerve).

In complete optic nerve lesion of one side (Amaurosis light reflex or total afferent pupillary defect)

The ipsilateral direct reflex is lost
The ipsilateral consensual reflex is intact
The contralateral direct reflex is intact
The contralateral consensual reflex is lost

In occulomotor nerve lesion of one side (efferent pupillary defect

The ipsilateral direct reflex is lost
The ipsilateral consensual reflex is lost
The cool ralateral direct reflex is intact
The contralateral consensual reflex is intact [/INST] question: A patient presented with normal eyesight and absence of direct and consensual light reflexes. Which of the following cranial nerves is suspected to be lesioned? | options: A: Occulomotor B: Trochlear C: Optic D: Abducent | answer: A </s>