I read with interest the recent article by Villegas RB and Ilsen PF, “Functional visual loss: A diagnosis of exclusion” (Optometry 2007;78:523-533). The authors have done an excellent job outlining and describing the wide variety and clinical presentation of patients with functional visual loss. I would, however, challenge the conclusion and title of the paper which indicates that functional visual loss is a diagnosis of exclusion. In fact, traditional teaching has held that functional visual loss is a positive diagnosis made by demonstrating physiologic impossibilities. There is no doubt that the prudent practitioner will want to rule out organic disease in many cases of suspected functional visual loss especially when clinical testing is confusing or inconclusive. It is also known that many patients will experience “functional overlay” of true organic disease further confounding an accurate diagnosis. It would be inappropriate, however, in all cases of functional visual loss to subject patients to an exhaustive battery of expensive and potentially risky testing when the diagnosis is positively established by demonstrating physiologic visual impossibilities. In these cases, reassurance, psychiatric evaluation, and careful follow-up would be the most appropriate management.