The trigeminal (V), an oft-neglected nerve.

Corneal denervation is one of the most serious insults that can occur to an eye; disease symptoms can be suppressed, and epithelial breakdown is likely to occur. In the cases presented, failure to test corneal sensation delayed diagnosis and endangered the cornea. Conditions affecting the trigeminal sensory pathway, including those causing a pain-anesthesia paradox, are described. Corneal sensation must be tested in all instances of suspicious head pain or paresthesia, head trauma, cranial nerve defect, cranial autonomic dysfunction, or unexplained corneal epithelial defect. The trigeminal nerve is often neglected, but corneal anesthesia aids in the diagnosis of intracranial disease and dictates the need for corneal observation and protection.