Pattern VEPs and long-term metabolic control (HbA1c) in juvenile diabetes

Purpose: How the pattern VEP at three spatial frequencies of stimulation can be alterated and/or influenced by different conditions of long-term metabolic control in patients affected by juvenile diabetes without any ophthalmoscopical and/or fluorangiographic sign of diabetic retinopathy. Methods: 50 juvenile diabetic patients (100 eyes), best corrected visual acuity 20/20, with an average age of 19.3 years (±4.79) were submitted at different spatial frequencies of stimulation pattern VEP (0.49,1.45,4.37cy/deg, reversing at 1.3 Hz, background luminance 50 cd/m2).The N1, P100 and N2 components had been singularly analyzed and related to the 4 years mean value of HbA1c (8.507% ± 1.47), the latter calculated on the basis of three blood samples per year. The patients were subsequently divided into two groups, relating to 4 years HbA1c value: I group 4yrs HbA1c< 8%; II group 4yrs HbA1c>8%. The resulting data was compared with a control group, matched for sex and age, and processed by Macintosh computer Statview II program. Results: For each spatial frequency of stimulation: 1) The latency of P100 was delayed in all the diabetic patients (respectively 0.49cy/deg P100= 103.89msec p<0.001, 1.45cy/deg P100=103.27msec p<0.001, 4.37cy/deg P100=121.36msec p<0.001).2) The latency of the N1 component was statistically significantly higher in the II group than in the I group (ANOVA test: 2.905msec at 0.49cy/deg, 2.708msec at 1.45cy/deg, 8.313msec at 4.37cy/deg). In addition, the latency of the P100 component was statistically significantly higher in the II group than in the I group at 4.37 cy/deg.(ANOVA test: 4.853 msec).Conclusions: An increase of the latency of N1 and P100 components at the highest spatial frequency supports the theory that in juvenile diabetes, without any ocular sign of disease, a subclinical functional alteration of the foveal area is present. The latency of the N1 component seems to be more sensible to the long-term metabolic condition and the difference with that of the P100 component support the hypothesis of a different origin of these two components.