In vivo Meibomian gland imaging techniques: A review of the literature

Meibomian gland dysfunction (MGD) includes a group of complex disorders of the ocular surface. It represents one of the main etiologies of dry eye as well as one of the main reasons for patient visits to the ophthalmologist. Classic clinical tests (dry eye symptoms, tear film break-up time, evaluation of gland expressibility or Schirmer's testing) only provide an indirect assessment of the function of the Meibomian glands and the meibum. Various in vivo testing methods have therefore been developed to image the Meibomian glands, such as Meibography, optical coherence tomography, ultrasound, or even in vivo confocal microscopy. Some are accessible in clinical practice, while others are limited to the realm of clinical research. All of these techniques aim to develop a direct structural analysis of the Meibomian glands so as to assist in the diagnosis of MGD as well as to better understand the pathophysiology of the Meibomian glands. This review of the literature hopes to provide an overview of the current imaging modalities and their role in the evaluation of the Meibomian glands and MGD.