Ocular herpes zoster is caused by varicella-zoster virus infection, but the infection is primarily due to the ophthalmic branch of the facial trigeminal nerve being affected. The trigeminal nerve is divided into three, with a maxillary branch, a mandibular branch, and an ophthalmic branch. Herpes zoster of the eye is an injury to the ophthalmic branch of the trigeminal nerve and usually occurs unilaterally. It appears as clusters of blisters around one side of the eye or on the forehead, and the eye may become swollen and painful, sometimes to a very severe degree. It can also cause corneal ulcers, conjunctivitis, and even blindness in severe cases. This type of herpes zoster is more common in the elderly and in people with low immune function, so when treating the ocular herpes zoster virus, it is important to have an ophthalmology consultation so that the ophthalmology department can assist the dermatology department with the treatment.