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I sought to examine the association between physical activity (PA) and mental health in adolescents with neurodevelopmental disorders, particularly those clinically diagnosed with attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD), and to investigate whether the retina, especially the retinal nerve fibre layer (RNFL), could serve as a new biomarker to monitor changes underlying these benefits. 1 RNFL axons are unmyelinated retinal ganglion-cell fibres that project to the lateral geniculate nucleus (LGN), offering a structurally proximal, central nervous system-related readout, because these fibres form the intraretinal (unmyelinated) segment of the optic nerve en route to their first synapse in the LGN. Optical coherence tomography (OCT)-measured RNFL thickness is increasingly used as a non-invasive index of neuroaxonal integrity in central nervous system (CNS) disorders, including ADHD and ASD. Moreover, given the known effects of stress and PA on neurotrophic and vascular pathways, it is plausible that retinal neurons and microvasculature may adapt in response, thereby making retinal metrics promising biomarkers.2