Relationship between fasted insulin levels and mfERG implicit times in patients with type 2 diabetes and prediabetes.

PURPOSE

It is established that the mfERG is altered in type 2 diabetes (T2DM). The P1 implicit time (IT) becomes delayed even before retinopathy is present. This has been associated with the duration of damage to retinal cells from hyperglycemia. However, patients withT2DM and prediabetes also have changes in insulin values. The impact of elevated or reduced blood insulin on retinal function using mfERG has not been explored. Here we evaluate the the relationship between blood insulin levels and mfERG parameters in patients with and without T2DM and prediabetes.

METHODS

66 subjects (age 50.4 ± 10.5) were included in this cross-sectional study. Subjects were asked if fasted upon presentation. HbA1c was taken and used to categorize subjects into groups as controls (< 5.7%), prediabetes (5.7-6.4%) or T2DM (> 6.4% or previously diagnosed). Insulin was collected from finger stick and was analyzed via ELISA. A mfERG (103 hexagons) was performed (VERIS 6.3) with 4-min m-sequence at near 100% contrast. Data was evaluated for ring hexagons, as well as averaged together for P1 IT. No subjects had retinopathy or were taking exogenous insulin. Data were evaluated through ANOVA for comparisons of groups and as well as with multivariate regression analysis.

RESULTS

There was a strong positive correlation between fasting blood glucose and mfERG IT (P < 0.002) in all subjects. There was also a negative relationship between averaged mfERG IT and fasted blood insulin concentration (P = 0.035) after age, T2DM duration and blood glucose were controlled for in a multivariate regression. There was a significant difference in mfERG IT between the groups (p = 0.008) with T2DM exhibiting the longest IT, but no difference between controls and prediabetes. There was no difference in insulin levels between groups, nor were there any significant relationships between insulin and mfERG IT for those who were not fasted.

CONCLUSIONS

Reduced blood insulin is associated with IT delays under overnight fasted conditions, which suggests a lack of insulin may impair retinal function. Future work should examine these associations of retinal function with insulin under well controlled and standardized postprandial conditions such as during oral glucose tolerance testing.