الفهرس 
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Abstract
Summary
Meibomian gland dysfunction (MGD) may well be the leading cause of dry eye disease throughout the world. Although this condition affects the health and well-being of millions of people, there is no global consensus on the definition, classification, diagnosis, or therapy for MGD.
There are several evidence-based explanations for the terminology used in this definition. The term dysfunction is used because the function of the meibomian glands is disturbed.
MGD may be classified according to anatomic changes, pathophysiological changes, or the severity of disease. Any classification system must meet the needs of the clinician and researcher alike. A classification based on pathophysiology is deemed to best meet these needs.
A classification of MGD into two major categories based on meibomian gland secretion is proposed: low-delivery states and high-delivery states. Low-delivery states are further classified as hyposecretory or obstructive, with cicatricial and noncicatricial subcategories.
Epidemiologic investigation of MGD has been limited because there is no consensus regarding the definition nor is there a standardized clinical assessment that characterizes this disease. There is a paucity of evidence on the natural history of MGD, the actual processes that cause it, or when symptoms actually develop in the disease process. It is also unclear whether MGD symptoms begin at the onset of or after meibomian gland damage and altered meibum delivery or instead arise from subsequent damage to other ocular surface tissues.
The diagnosis of MGD, whether in isolation or associated with ocular surface damage or dry eye, should be viewed in the context of diagnosing any ocular surface disease. Tests should be performed in an order that minimizes the extent to which one test influences the results of the tests that follow.
A series of tests that are recommended for use in the diagnosis of MGD and in MGD-related disorders, including evaporative dry eye are now available.
Treatment of MGD varies greatly among eye care providers on different continents. Underreporting makes it difficult to assess practice patterns accurately, but most practitioners agree that underdiagnosis is common and clinical follow-up irregular. Without generally accepted definitions for a staging system of clinical severity of MGD, it is problematic to propose a treatment plan based on disease stage.