Injury to which of the following structures causes constricted pupils even when room lighting is dim?
Postganglionic sympathetic fibers that originate from the superior cervical ganglion and innervate the dilator pupillae (radial muscles of the iris) are damaged. So the pupil remains small in a dimly lit room. Other nerves mentioned contain no sympathetic fibers, but the oculomotor nerve contains preganglionic parasympathetic fibers.
Trochlear nerve
Superior cervical ganglion
Oculomotor nerve
Ophthalmic nerve
Neuroanatomy 3