Retinal vascular reactivity is associated with white matter hyperintensities and dysfunctional cerebrovascular reactivity in cerebral small vessel disease.

Cerebral small vessel disease (cSVD) is characterised by white matter hyperintensities (WMH) and contributes to stroke and dementia. Cerebrovascular reactivity (CVR) declines with worsening cSVD but estimates of CVR from brain scans give limited information about the coordination of individual arterioles or venules. Retinovascular reactivity can provide separate data about arterioles and venules, but it is not known if retinovascular reactivity correlates with CVR in people with cSVD. We aimed to assess retinal vascular reactivity in people with cSVD and explore associations with WMH and CVR in a cross-sectional study. Participants had retinal photographs and magnetic resonance brain imaging (MRI) before and during inhalation of 6% CO₂ in air. We recruited 60 participants. 48 provided analysable retinal vessel reactivity data. Retinal arteriole/venule ratio was inversely related to WMH severity (adjusted R2 = 0.47 β-5.2 95%CI-7.9 to -2.5) and directly related to CVR (adjusted R2 = 0.21 β0.15 95%CI 0.04 to 0.25). In general, participants whose arteriole/venule ratio increased with CO₂ had milder WMH and higher (better) CVR, while participants whose arteriole/venule ratio decreased had more severe WMH and lower (worse) CVR. Retinovascular reactivity to CO₂ inhalation in people with cSVD suggests loss of normal arteriovenous coordination and inefficient perfusion of the capillary bed.