Background: To analyse the microscopic anatomy of the orbicularis oculi muscle in patients with congenital epiblepharon and to determine whether hypertrophy of the orbicularis oculi muscle, which is considered as a possible cause of this eyelid malposition, exists.
Methods: Sixty-seven eyelids with congenital epiblepharon of 41 Japanese patients, as well as 30 control eyelids of 24 Japanese patients with other eyelid pathologies (upper eyelid: fourteen blepharoptosis, one trichiasis and two retractions; lower eyelid: five involutional entropions, one trichiasis and seven retractions) were analysed. These controls contained no orbicularis pathology such as cicatrization or orbitopathy. The muscle specimens were obtained from the central part of the pretarsal orbicularis oculi muscle during surgery. The specimens were stained with haematoxylin & eosin. Only specimens with cross-sectional areas that included large muscle fibres were selected. In each section, 10 muscle fibres were measured across their smallest diameter, thereby avoiding inaccurate measurements of muscle kinking occurring during the processing or by any obliquity of the plane of section. Measurements of the muscle fibre diameter were made with a digital measure.
Results: There were no significant differences in the average diameter of the muscle fibres between the patients with congenital epiblepharon and the control group.
Conclusions: There was no evidence of orbicularis oculi muscle hypertrophy in congenital epiblepharon.