This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optic Nerve, Subject name: Ophthalmology
An optic nerve injury may result in all of the following except. 
Select and explain. 
A. Loss of vision in that eye., B. Dilatation of pupil., C. Ptosis, D. Loss of light reflex.
C: Ptosis
Answer: C: Ptosis 
Explanation: Ans. is 'c' i.e. Ptosis Ptosis is not seen in optic nerve injury. It is the drooping of upper eyelid d/t the paralysis or defective development of LPS. LPS is supplied by oculomotor N (III N)About other options:Optic nerve carries different fibres for both visual pathway and light reflex. So an injury to the optic n. will obviously result in loss of vision and loss of light reflex.About option B (i.e. dilatation of pupil)In text book of head injury by A.K. Mahapatra it's written that Optic nerve injury can lead to dilatation of pupil. "when a patient is unconscious, unilateral fixed dilated pupil with retained consensual light reflex raises the possibility of unilateral optic nerve injury (Marcus Gunn Pupil)."