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Oliver Niels Klefter, Michael Larsen; Influence of Baseline HbA1c on Electroretinographic Changes During Long-term Insulin Pump Therapy. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2448.
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To investigate if baseline haemoglobin A1c (HbA1c) influenced the long-term effects of insulin pump therapy (CSII) on retinal function in adult patients with type 1 diabetes mellitus.
Twelve eyes of 12 patients with type 1 diabetes whose retinal function had been studied before and 1 week, 1, 4 and 12 months after CSII initiation were examined at a follow-up visit 3.5 years after baseline. Two groups (high and low) were defined using median baseline HbA1c (8.65%) as the cut-off point. Mixed model analysis with post-hoc Tukey tests was used to compare changes in full-field electroretinographic amplitudes and latencies in the two groups across time points. Continuous variables were compared by simple linear regression.
Changes in the electroretinographic amplitudes over time differed between the HbA1c groups. Specifically, differences were found in the rod response (p < 0.001), a- and b-wave of the rod-cone response (p < 0.001 and p < 0.01, respectively), first and second oscillatory potential (both p < 0.05), a- and b-wave of the photopic cone response (both p < 0.01) and the photopic flicker response (p < 0.05). During the first year of therapy amplitude changes were similar in the two groups. The observed intergroup differences were caused by significant amplitude reductions in the high group at the 3.5-year visit. In the low group amplitudes did not change significantly from baseline. No intergroup differences were found in the third and fourth oscillatory potentials or the photopic flicker response. A difference in latency changes was only observed for the rod response which became faster in the high group and slower in the low group at the 3.5-year visit (p = 0.03). Baseline HbA1c was negatively correlated with changes in HbA1c at the 1-month, 1-year and 3.5-year visits (all p < 0.01). HbA1c did not differ significantly between the groups at the follow-up visit.
Reduced electroretinographic amplitudes were observed after long-term CSII therapy in patients with high baseline HbA1c. The highest baseline levels, however, allowed for the largest improvements in glycaemic control which might also per se have contributed to the observed changes in retinal function, a potential subclinical equivalent to the early worsening phenomenon. It remains to be determined if functional alterations can predict changes in diabetic retinopathy level.
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