Which area is least likely to be affected by a herpes simplex keratitis lesion?

• A. Lateral upper eyelid
• B. Medial upper eyelid
• C. Lateral lower eyelid
• D. Forehead

Answer: (C)

Herpes simplex keratitis lesions tend to follow the sensory nerve pathways that supply the cornea, mainly the nasociliary branch of the ophthalmic division of the trigeminal nerve. The nasociliary nerve and its branches innervate the medial canthus and medial eyelid regions, so these areas are more commonly involved as the virus tracks along those pathways. The lateral lower eyelid, by contrast, is primarily supplied by the infraorbital nerve from the maxillary division, a different nerve pathway, making it least likely to be affected by a keratitis lesion. The forehead is served by the frontal nerve (supraorbital and supratrochlear branches), which is another V1 distribution, but keratitis-related changes more reliably align with the nasociliary territory, so the lateral lower eyelid stands out as the least likely site.