Abstract
BACKGROUND: In vivo confocal microscopy (IVCM) is a vital tool in studying dry eye disease (DED), providing insights into morphological changes at ocular surface unit levels. This review presents the main differences in corneal structure between aqueous-deficient dry eye disease (AD-DED) and normal eyes. METHODS: A comprehensive search of PubMed, Web of Science, Embase, and MEDLINE databases from January 2000 to December 2023 was conducted. The study selection process, as well as data selection and examination, were independently performed by two members of the review team. RESULTS: The review reveals a consistent decrease in corneal surface epithelial cell density in AD-DED cases compared to a control group, but conflicting data on basal epithelial cell density. Notably, the abnormal hyperreflectivity of keratocytes in patients with Sjogren's syndrome was recorded, and there was a significant keratocyte density in AD-DED subjects compared to evaporative DED and control groups. Studies also found a decrease in sub-basal nerve density, increased tortuosity, and the fragmentation of nerve fibers. Dendritic cell density and dendritic cell dendrites increase in AD-DED patients compared to healthy subjects. CONCLUSIONS: IVCM is a powerful tool for enhancing our understanding of the pathophysiological mechanisms underlying DED. However, the review underscores the urgent need to standardize the terminology, analysis, and units used for accurate interpretation, a crucial step in advancing our knowledge of DED.