Final answer:
The oculosympathetic pathway controls pupil dilation in response to low light levels. Horner's syndrome and diagnostic tests can help determine the location of a sympathetic lesion without using drops like cocaine or apraclonidine.
Step-by-step explanation:
The oculosympathetic pathway is responsible for controlling the dilation of the pupil in response to low light levels. It involves the sympathetic division of the autonomic nervous system and includes several structures such as the superior cervical ganglion and the iris. Clinically determining the location of a sympathetic lesion without using drops like cocaine or apraclonidine can be done by assessing for certain symptoms such as Horner's syndrome or considering other diagnostic tests like imaging studies.