Background/Aim The aim of this study was to evaluate the effect of prediabetes and diabetes on macular thickness and retinal vascular calibres in our population-based cohort (Northern Finland Birth Cohort).

Methods The population of 2005 individuals was divided into diabetes (n=57), prediabetes (n=1638) and normal glucose metabolism (NGM) groups (n=310). Total thickness of the macula was measured using Cirrus HD-OCT 4000. Central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE) calibres were measured from the fundus images. The diagnosis of diabetes and prediabetes was made according to WHO 2006 diagnostic standards.

Results Significant macular thinning was observed in subjects with prediabetes (−2.69 μm (95% CI −4.29 to −1.09), p<0.05 and −0.10 mm³ (95% CI −0.16 to −0.04), p<0.05 for macular cube average thickness and cube volume, respectively) and it was greatest in the pericentral area. Macular cube average thickness and macular cube volume decreased significantly by worsening glucose metabolism. Furthermore, CRAE was decreased by increases in 2-hour post-load glucose, glucose area under the curve and increase in Matsuda index (p<0.001, 0.019 and <0.001, respectively). In mediation analysis, macular thickness had significant average causal mediation effect (ACME) on CRVE and CRAE in subjects with prediabetes.

Conclusion We detected significant thinning of the macula in subjects with prediabetes. The diameters of retinal arteries were decreased by impaired glucose metabolism. This study provides a new perspective since it revealed that the early and subtle changes caused by prediabetes as macular thinning had significant ACME on retinal vessels, therefore supporting the neurodegenerative theory of diabetes-induced changes in the retina.