Retinal microvascular alterations consistent with endothelial dysregulation in paediatric post-COVID-19 syndrome: A prospective matched-cohort study.

Persistent symptoms following SARS-CoV-2 infection in children remain poorly understood, and objective biological correlates are scarce. The vascular endothelium is considered a central target of post-viral dysregulation, yet paediatric evidence for microvascular involvement is limited. Retinal imaging enables non-invasive assessment of microvascular structure and function and may help to clarify whether endothelial dysregulation is present in children with post-COVID-19 syndrome (PCS). Retinal vessel diameters and flicker-induced vasoreactivity were assessed at baseline and after a median of 14 weeks. Compared with matched healthy controls, multivariable analyses showed that PCS independently predicted wider central retinal arteriolar equivalent (CRAE + 28.1 μm, 95% CI 21.7-34.5, p < 0.001) and central retinal venular equivalent (CRVE + 21.7 μm, 95% CI 15.8-27.7, p < 0.001), with a higher arteriolar-to-venular ratio (AVR + 0.038 units, 95% CI 0.012-0.064, p = 0.005). These findings suggest a distinct microvascular pattern in children with PCS that is consistent with endothelial dysregulation months after infection. While no significant group-level changes were observed at follow-up, children with particularly large venular diameters and reduced flicker responses showed the greatest improvement. Longer follow-up intervals predicted decreasing venular diameter, and reductions in symptom burden correlated with increasing AVR over time. Together, these results indicate heterogeneous, time-dependent changes in microvascular parameters. Retinal vessel analysis may provide a useful, non-invasive approach to characterising vascular involvement in paediatric PCS and improving understanding of post-viral sequelae.