Normal vision with absence of direct & consensual light reflex, which nerve is involved ?
Ans. is 'b' i.e., Oculomotor This question can be solved by simple basic knowledge :-Among the given options only oitic nerve and occulomotor newes are related to light reflex'a In optic nerve injury vision is also impaired (vision is normal in the question)'n Thus answer is oculomotor nerve When light is shone to one (e.g. left) eye. left optic nerve canies afferent impulse to brain and from brain efferent impulse to ipsiplateral (left) eye comes through ipsilateral (left) occulomotor nerye (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) eyc, 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 effcrent fbr left eye (for consensual light reflex) comes through left occulomotor nerve' So :- Optic newe is responsibtefor direct light reJlex in ipsilateral eye and consensual light reflexfor contralateral eye. (lnabove example, afferent for right sided direct and left sided consensual light reflex is through right optic nerve; and atl-erent 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' (ln above example' efferent for right sided direct as rvell as consensual light reflex is through right occulmotor nerve and ef'ferent 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 fect) The ipsilateral direct reflex is lostThe ipsilateral conscnsual reflex is intactThe contralateral direct reflex is intactThe contralateral consensual reflex is lost In occulomotor nerve lesion ofone side (efferent pupillarydefect The ipsilateral direct reflex is lost The ipsilateral consensual reflex is lost The contralateral direct reflex is intact The contralateral consensual reflex is intact
Optic
Oculomotor
Trigeminal
Abducens