Effects of Physical Activity Level on Microsaccade Dynamics During Optic Flow Stimulation in Adults with Type 2 Diabetes

<b>Background</b>: Microsaccades are small fixational eye movements tightly linked to attention and oculomotor control. Although diabetes mellitus is associated with retinal and neural alterations that may impair visuomotor function, the influence of physical activity on microsaccade behaviour in individuals with type 2 diabetes mellitus (T2DM) remains unknown. This study investigated whether habitual physical activity modulates microsaccade characteristics during fixation under different optic flow stimuli. Given that optic flow engages motion processing and gaze stabilisation pathways that may be affected by diabetes-related microvascular/neural changes, it can reveal subtle visuomotor alterations during fixation. <b>Methods</b>: Twenty-eight adults with T2DM and no diagnosed retinopathy performed a fixation task while viewing optic flow stimuli made of moving dots. Eye movements were recorded using an EyeLink system. Physical activity behaviour was assessed at baseline and at a 6-month follow-up after a low-threshold aerobic circuit training programme. Classification as physically active (≥600 MET-min/week) or inactive (<600 MET-min/week) was based on the 6-month assessment. Microsaccade characteristics were analysed by repeated-measures ANOVA. <b>Results</b>: Microsaccade rate was modulated by optic flow (<i>p</i> = 0.044, η²p = 0.106) and showed a significant stimulus × group × sex interaction (<i>p</i> = 0.005, η²p = 0.163), indicating sex-dependent differences in how optic flow modulated microsaccade rate across physically active and inactive participants. A time × stimulus interaction effect was found in peak velocity (<i>p</i> = 0.03, η²p = 0.114) and amplitude (<i>p</i> = 0.02, η²p = 0.127), consistent with modest context-dependent changes over time. <b>Conclusions</b>: These findings suggest that physical activity modulates microsaccade generation and supports the potential of microsaccade metrics as sensitive indicators of oculomotor function in diabetes.