Higher Total Insulin Dose Has Positive Effect on Corneal Nerve Fibers in DM1 Patients

Neuropathies are among the most common long-term complications of diabetes mellitus (DM) and good glycemic control is essential in prevention of this complication. DM patients with similar mean glucose levels or HbA1c levels often exhibit differences in glucose variability. We tested for possible associations between parameters of glycemia compensation and corneal sub-basal nerve fiber status.

The study included 20 patients with DM type 1 treated using an intensified insulin regimen. The corneas of both eyes were examined using in vivo corneal confocal microscopy. Corneal nerve fiber density (NFD), nerve fiber length (NFL), and nerve branch density (NBD) were evaluated. Possible associations between parameters of glycemia compensation (HbA1c, glycemia SD, and insulin dose), and other clinical factors were analyzed.

NBD was the highest in those with higher glycemic variability (P = 0.023). HbA1c had a negligible effect on corneal nerve parameters. NFD, NFL, and NBD were statistically significantly higher in those with higher total insulin per kilogram (P = 0.02, P = 0.01, and P = 0.012, respectively). Among other factors, a positive correlation between free thyroxine (fT4) levels and NFD and NBD was also found (P = 0.041 and P = 0.015, respectively).

Total insulin dose per kilogram may be an important factor influencing nerve fiber status and needs to be considered in future studies of diabetic neuropathy pathophysiology and its progression. Also, more attention must be paid to other possible factors when elucidating the development of diabetic complications.