The relationship between morphology and function of the meibomian glands

Meibomian gland dysfunction (MGD) is a leading cause of dry eye disease (DED). Meibomian gland dysfunction is divided into two major categories based on meibomian gland secretion: low delivery and high delivery. The low-delivery states are further classified as either hyposecretory or obstructive subtype, and the high-delivery state is termed “hypersecretory MGD.” Two parameters are commonly used to evaluate meibomian gland function: lipid layer thickness and meibum quality and expressibility. To evaluate the morphology of meibomian glands, meibography is used to detect meibomian gland dropout. Functional and morphological changes of meibomian glands are often thought to be well correlated; in reality, many cases do not because some patients have characteristics of both hypersecretory and obstructive subtypes. We suggest that the MGD classification system should be modified to include a mixed subtype to explain such patients.