Commentary: The electromyographic analysis of orbicularis oculi muscle in epiphora.

Abstract

The simplest description of functional epiphora is “epiphora in the presence of a patent lacrimal drainage system, absence of any demonstrable anatomical abnormality, and absence of alternative etiology.”[1] It is a complex and underdiagnosed entity. Jones, in 1957, suggested dysfunctions of the lacrimal pump as the major aberration in functional epiphora.[2] Ali et al.,[3] in 2020, presented a new theory of lacrimal pump functions based on their anatomical, ultrastructural, and immunohistochemical studies of the Horner–Duverney (HD) muscle. The diagnosis of functional epiphora is by a series of examinations and imaging to exclude other causes. In essence, it is a diagnosis of exclusion. Hence, a careful clinical examination along with magnetic resonance dacryocystography or dacryoscintigraphy are helpful.[4] The data on the use of electromyography (EMG) and its characteristics in such cases is evolving. The present study succinctly described the electromyographic response of the deeper heads of the orbicularis oculi muscle using the motor unit potential (MUP) analysis.[5] A statistically significant change in the amplitude, duration, number of phases, turns, and rise time were noted between the functional epiphora cohort and normal volunteers. The EMG was suggestive of a neurogenic origin of lacrimal pump weakness in patients with functional epiphora. Apart from the earlier known motor innervation by the branches of the facial nerve, recent other explorations have pointed to the presence of an extensive network of additional sensory, sympathomimetic, and parasympathetic innervation of the HD muscle.[3] Hence, the EMG needs to be further explored. Although the present study had several limitations, including difficulties with the not very conclusive results, it is nevertheless an excellent strategy to begin answering the proposed research query. To what extent can an EMG help appreciate the complex physiology of the HD muscle is yet to be deciphered. Although EMG partly enhances our understanding of the orbicularis oculi behavior in different clinical settings, it does not directly assess the lacrimal pump mechanisms of tear flow. Besides, it is unhelpful to assess other mechanisms in tear flow dynamics such as capillary action, gravity, and pressure gradient. At present, EMG of the HD muscle has limited clinical worth and, at best, can be of adjunctive value. However, its utility as a research tool has the potential to further our understanding of the lacrimal pump. Financial disclosure Mohammad Javed Ali receives royalties from Springer for the textbook “Principles and Practice of Lacrimal Surgery,” “Atlas of Lacrimal Drainage Disorders,” and “Video Atlas of Lacrimal Surgery.”