Overthinking V1

HZO (herpes zoster ophthalmicus) is a recrudescence of VZV (varicella zoster virus) from the trigeminal nerve (cranial nerve V) ganglion, particularly an inflammation of the ophthalmic (V1) branch of the trigeminal nerve.

image credits:  Gray's Anatomy

The trigeminal nerve is mostly a sensory nerve, but is also a motor nerve. The maxillary (V2) and mandibular (V3) branches are also useful for biting, chewing and swallowing aside from sensory functions. The ophthalmic (v1) branch is a purely sensory branch.

After the inflammation has subsided and serious ocular complications have aborted, one may test neurologically the extent of nerve damage on V1. V1 supplies sensory innervation to the skin of the eyelids, eyebrow, forehead, nose, cornea, ciliary body, iris, lacrimal gland, conjunctiva, and part of the nasal mucous membranes.

• Test the corneal reflex
• Test for pain (light touch and pinprick)
• Test for temperature 
• Compare the left side with the right
• If sensory deficit is found, determine the edges affected

CORNEAL REFLEX
A normal person should blink when a wisp of cotton is brushed against the lateral aspect of the sclera. V1 receives sensory input from the surface of the eye. Blinking also requires an intact facial nerve (CN7) efferent function, since it provides eye lid closure.

If both sides of the face fail to contract, a V1 nerve lesion is suspected. If unilateral facial palsy is observed, a CN7 lesion is suspected. A reduced corneal sensation may be noted by the examiner, comparing both left and right sides, which may point to partial V1. An absent corneal reflex is an early sign of sensory trigeminal lesion.

MOTOR LIMB FUNCTION
To make the neurologic examination of the trigeminal nerve more thorough, examine the muscles of mastication, which is efferently innervated by the V3 nerve. Inspect for signs of temporal wasting and lateral deviation of jaw to the side of the lesion. Test for teeth clenching, mouth opening, and jaw diversion.

Just like any other disease, know that if you feel anything wrong, do not hesitate to ask your primary care doctor about it. Prevention beats any measure of cure.