Purpose
Although the double rows of meibomian gland orifices (MGOs) have been occasionally seen in daily clinical practice, little is known about their histological structure and influences on the ocular surface. We investigated lid margins and meibomian glands of healthy children and adults and cadaver eyelid tissue to explore the incidence, function and structure of double row MGOs.
Methods
Subjects of in vivo observation consisted of children undergoing strabismus surgery under general anesthesia (13 boys and 13 girls) and healthy adult volunteers (56 men and 30 women). The number of MGOs and presence of double row MGOs were obtained after induction of general anesthesia. The eyelid width, number of MGOs in the upper and lower eyelids, fluorescein staining score, tear break-up time (BUT), meibum expressibility grade, tear meniscus height, Schirmer tear production test, meiboscores obtained by non-contact meibography (Topcon Corp.), non-invasive BUT and tear meniscus height measured by Keratograph5M (OCULUS Inc.) and eyelid thickness were obtained in adult men.<br /> Histological investigation was conducted on 13 cadaver eyelid tissues (8 men and 5 women). Continuous horizontal sections with hematoxylin and eosin staining were obtained and observed by light microscope.<br /> “Double rows” were defined where more than 5 orifices were aligned in a second row distinctly separate from the primary row. This study was approved by the institutional review board of University of Tokyo School of Medicine, and adhered to the tenets of the Declaration of Helsinki.
Results
Among all subjects, double row MGOs were observed only in upper eyelids and never in lower eyelids. The incidences of the double rows MGOs were 30.7% in children, 32.1% in adult men, 30.0% in adult women, and 30.8% in elderly cadaver eyelids.<br /> Among adult men, the numbers of orifices in the upper eyelid was significantly higher in the double row group (n=18) compared to the single row group (n=38) (46.4±4.8 v.s. 36.0±5.3, p<0.0001). All other measurements were not statically different.<br /> In histological observation, orifices were connected to the central ducts on a one by one basis in both the single and the double row groups.
Conclusions
Double row MGOs exist in about 30% of upper eyelids among healthy Japanese. They are thought to be congenital and one of the anatomical variations of Meibomian gland arrangements with normal function.