Corneal Nerve Changes in Diabetes: A Meta-Analysis of In Vivo Confocal Microscopy Studies

Diabetes mellitus is a chronic disease that has adverse effects on the nervous system and thus results in diabetic peripheral neuropathy (DPN). Corneal nerves are among the first to be damaged when one is diagnosed with diabetes; they can, therefore, be used to diagnose neuropathy because they are easy to analyse. This systematic review and meta-analysis, therefore, aimed at identifying the usage of in vivo confocal microscopy (IVCM) on corneal nerve changes or density in diabetic patients, employing various parameters of corneal nerve density work, including CNFD, CNBD and CNFL. The article search involved PubMed, Embase, Scopus, and Web of Science, and studies were considered in accordance with the defined criteria. Data analysis was performed, including Random Effect Models, to combine the outcomes of the studies according to the type of diabetes and the degree of glycemic control. In order to determine the stability of the conclusions made by the study, sensitivity analysis was also conducted as well. A reducing pattern was manifested by diabetic patients for CNFD, CNBD as well as CNFL compared to control subjects. Microangiopathy was observed at all stages of diabetic neuropathy in both T1DM and T2DM groups, but T1DM was observed to have more severe changes than T2DM. These results confirmed that the glycemic control of the patients was inversely proportional to nerve fibre characteristics, indicating the damaging effects of hyperglycemia on the nerves. IVCM has shown valuable information on the early stage of DPN on corneal nerve fibre changes in patients with diabetes. IVCM can be, therefore, used as an optimal non-invasive approach to disease early detection and monitoring of diabetic neuropathy. It has the potential to be implemented into clinical practice to enhance diabetes management and avoid potential complications. Studies can also be conducted to define the guidelines for the use of IVCM and extend its application across different fields.