Corneal nerve fiber length (CNFL) represents a biomarker for diabetic distal symmetric polyneuropathy (DSP). We aimed to determine the reference distribution of annual CNFL change, the prevalence of abnormal change in diabetes, and its associated clinical variables.We examined 590 participants with diabetes [399 type 1 diabetes (T1D) and 191 type 2 diabetes (T2D)] and 204 control patients without diabetes with at least 1 year of follow-up and classified them according to rapid corneal nerve fiber loss (RCNFL) if CNFL change was below the fifth percentile of the control patients without diabetes.Control patients without diabetes were 37.9 19.8 years old, had median follow-up of three visits over 3.0 years, and mean annual change in CNFL was -0.1% (90% CI, -5.9 to 5.0%). RCNFL was defined by values exceeding the fifth percentile of 6% loss. Participants with T1D were 39.9 18.7 years old, had median follow-up of three visits over 4.4 years, and mean annual change in CNFL was -0.8% (90% CI, -14.0 to 9.9%). Participants with T2D were 60.4 8.2 years old, had median follow-up of three visits over 5.3 years, and mean annual change in CNFL was -0.2% (90% CI, -14.1 to 14.3%). RCNFL prevalence was 17% overall and was similar by diabetes type [64 T1D (16.0%), 37 T2D (19.4%), P = 0.31]. RNCFL was more common in those with baseline DSP (47% vs. 30% in those without baseline DSP, P = 0.001), which was associated with lower peroneal conduction velocity but not with baseline HbA1c or its change over follow-up.An abnormally rapid loss of CNFL of 6% per year or more occurs in 17% of diabetes patients. RCNFL may identify patients at highest risk for the development and progression of DSP.