In vivo confocal microscopy of the cornea is a non-invasive, rapid, and comprehensive technique for real-time, dynamic observation of all layers of the cornea. Confocal microscopy allows the examination of the morphology and cell density in the different layers of the cornea through direct visualization. With the increasing prevalence of diabetes, ocular complications have become common and have garnered more interest and in-depth research from clinical and scientific communities. This paper provides a comprehensive review of research progress made using in vivo confocal microscopy to observe various layers of cornea tissue in diabetic patients.