The eye and the brain share embryological, anatomic and physiological similarities, which suggest that the retinal microvasculature may be an ideal surrogate marker of cerebrovascular function. This is intriguing, as the cerebral vasculature cannot be directly measured in a non-invasive manner. In epidemiological studies abnormal retinal Arteriovenous Ratios (AVR) are associated with an increased risk of stroke and cerebrovascular disease. However, the association between retinal vasoreactivity measurements and cerebral blood vessel function remains unknown. An attenuated retinal vasoreactivity may indicate endothelial dysfunction in the eye and brain and may prove to be useful as a marker of cerebrovascular disease in high risk populations such as in diabetics.
STUDY GOALS:
To examine 1) the impact of diabetes at different disease stages on measures of cerebrovascular function and 2) the relationship between retinal blood vessel reactivity, retinal AVRs and measures of cerebral small vessel function.
METHODS:
This cohort study included 29 type 2 diabetics, 14 pre-diabetics, and 14 healthy controls (ages: 37 to 75 years). Retinal vasoreactivity was measured with the Dynamic Vessel Analyzer (Imedos, Jena, Germany) following high frequency flicker light stimulation. Cerebrovascular blood flow velocity of the Middle Cerebral Artery (MCA) was assessed by Transcranial Doppler Ultrasound (TCD) (Siemens, USA).
RESULTS:
Progression of diabetes was found to be significantly associated with attenuation of light flicker stimulus response (P=0.0009 artery, P=0.0001 vein, CI 95%), AVR (P=0.0070, CI 95%), PI (P=0.0202, CI 95%), RI (P=0.0033, CI 95%) and hyperventilation-breath hold (P≤0.0001, CI 95%). Across all groups, attenuated retinal arterial and venous diameter responses to the light flicker stimulus were associated with an increase in MCA RI (P=0.02, r=-0.30 artery, P=0.06, r=-0.24 vein, CI 95%). An attenuated venous diameter response was associated with an increase in PI (P=0.02, r=-0.29 vein, CI 95%). In addition, attenuated retinal diameter responses were also associated with a decrease in MCA mean flow velocities following hyperventilation-breath hold (P=0.05, r=0.26 artery, P=0.01, r=0.34 vein, CI 95%). Attenuated retinal responses were also correlated with a reduction in AVR (P=0.05, r=0.26 artery, P=0.15, r=0.19 vein, CI 95%).
CONCLUSION:
Impairment of retinal vasoreactivity is associated with cerebrovascular dysfunction across the continuum of diabetes, possibly indicating that the eye reflects changes in cerebral blood vessel function and stroke risk.
Rhythmic light flicker rescues hippocampal low gamma and protects ischemic neurons by enhancing presynaptic plasticity
