The nasociliary nerve is a branch of the ophthalmic nerve, which is part of the trigeminal nerve (cranial nerve V). It primarily provides sensory innervation to the structures in the eye and surrounding areas, including the cornea, the nasal cavity, and parts of the forehead. This nerve also gives rise to several smaller branches, such as the long ciliary nerves and the ethmoidal nerves, which further supply sensation to the eye and the nasal passages. Understanding the nasociliary nerve is important in fields like ophthalmology and neurology, as it plays a crucial role in eye health and sensory perception.