The reactivation of the varicella-zoster virus may lead to a chronic stage of neuralgic pain. A study was developed to investigate the neuropathology of the condition. The temperature of the ocular surface was measured following a non-invasive procedure. A negative thermal gradient was encountered, being the affected eye much colder than the contralateral eye. It is understood that the temperature of any area of the body is regulated by the state of its vascular supply and, in turn, vasoconstriction is sympathetically mediated. Thus, lower temperatures may arise from a sympathetic hyperactivity or from a supersensitivity of sympathetic receptors. Alternative hypotheses are also explored.