Herpes zoster ophthalmicus primarily affects which cranial nerve?

Herpes zoster ophthalmicus primarily affects the first division of the trigeminal nerve, which is known as cranial nerve V1. This region innervates the forehead, upper eyelid, and parts of the nose, making it particularly vulnerable to infection by the varicella-zoster virus, especially when it reactivates as herpes zoster (shingles).

The involvement of CN V1 in herpes zoster can lead to significant complications, such as keratitis, conjunctivitis, and possibly vision loss, as the virus can affect the eye structures and the surrounding areas. The specific symptoms often include vesicular lesions on the forehead and eyelids, along with ocular manifestations.

Understanding the pathways of these cranial nerves is crucial, as it helps to diagnose and manage potential complications of herpes zoster effectively. For example, the second division of the trigeminal nerve (CN V2) innervates the midface and does not typically involve the ocular region, which is predominantly supplied by CN V1. Similarly, CN V3 is responsible for the lower face and jaw, and CN VII is the facial nerve influencing muscles of facial expression but is not related to the ophthalmic area affected by herpes zoster. Therefore, recognizing the specific