Prediabetes is associated with significant thinning of the macula and with decreases in retinal-artery diameters, according to a population-based study. "The changes in the macula showed a significant causal effect on retinal vessels," Dr. M. Johanna Liinamaa of Oulu University Hospital and Oulu University Faculty Of Medicine, in Finland, told Reuters Health by email. "This supports the theory that diabetes-induced changes in the retina are of neurodegenerative origin." Various retinal changes have been reported in individuals with impaired fasting glucose or hyperglycemia, but it remains unclear whether the initial prediabetic changes are vascular or neurally based. Dr. Liinamaa and colleagues used data from the Northern Finland Birth Cohort to evaluate the thickness of the macula in conjunction with retinal artery and venule caliber in 300 individuals with prediabetes, 57 with diabetes and 1,638 with normal glucose metabolism. People with prediabetes had significantly decreased mean macular thickness (280.5 um vs. 282.3 um among those with normal glucose metabolism) and significantly decreased mean macular volume (10.0 mm3 vs. 10.1 mm3), the researchers report in the British Journal of Ophthalmology. Macular thickness was significantly reduced in the prediabetic group in all nine subfields of the macular thickness map, with the greatest changes observed in the pericentral area. Macular thickness in the pericentral area was also significantly reduced in the diabetic group, compared with the normal group, but decreases in other subfields of macula were not statistically significant. Higher quintiles of plasma glucose measures were associated with significant decreases in macular thickness, macular volume and ganglion-cell-layer thickness. Increases in plasma glucose measures were also associated with significant decreases in central retinal arteriolar caliber and with nominal (but statistically insignificant) decreases in central retinal venular caliber. In causal mediation analyses, macular thickness appeared to cause the changes in vascular caliber and not vice versa. "The basis of the complications of diabetes appears very early and therefore it is important to prevent the onset of type 2 diabetes," Dr. Liinamaa said. "It is important for physicians to take action at the prediabetes stage in order to avoid diabetes-induced microvascular diseases, such as retinopathy." "Weight loss, exercise, and change in dietary habits will decrease the risk of getting type 2 diabetes," she said. "This would be beneficial also to ocular health." —Will Boggs MD Source
