To determine the cutoff values of fasting plasma glucose (FPG) variability for detecting retinopathy and examine the threshold of FPG levels for predicting retinopathy incidence in type 2 diabetes.

Subjects comprised 170 patients with type 2 diabetes who had no retinopathy at their first visit, and continuously visited thereafter for 27 years. Retinopathy was evaluated by ophthalmologists at least annually.

114 patients developed retinopathy. 46 of them had advanced retinopathy. The optimal cutoff values of intrapersonal mean and standard deviation (SD) of FPG over 27 years and intrapersonal mean HbA1c from the initial measurement to the last visit for detecting retinopathy were 7.4 mmol/L, 1.4 mmol/L, and 7.2% (56 mmol/mol), respectively. Similarly, for advanced retinopathy, 7.7 mmol/L, 1.9 mmol/L, and 7.5% (59 mmol/mol), respectively. Hazard ratios of deciles of intrapersonal mean FPG (mmol/L) during the initial 2 years for retinopathy incidence significantly increased from eighth-decile (6.9–7.4), and were sharply elevated from ninth-decile (7.4–8.7).

Our study provides new cutoff values for FPG variability. Cutoff values of FPG and HbA1c were slightly higher than recommended targets of the current guideline. The threshold of FPG levels (6.9 mmol/L) is proposed to predict retinopathy incidence during the subsequent 25 years.