Characterising the Time Course of the Dilatory Response of Healthy Retinal Arteries during Flicker-Light Provocation.

Introduction: The dilatory response of healthy retinal arterioles to flicker-light (FL) provocation appears to be biphasic. The vessel diameter rapidly increases (acute phase) over 5-10 s, then barely increases thereafter (maintenance phase) until FL cessation. This reaction is usually characterised at a single point by two parameters: maximum dilation (MD) relative to baseline diameter (MD, %) and time to MD (RT, s). This paper describes the biphasic reaction of retinal arteries during FL provocation using a bi-linear function.

Methods: Retinal arterioles from 45 adults were examined during flicker provocation. Each individual time course of arterial diameter change during FL provocation was characterised by a bi-linear equation and compared with MD and RT.

Results: Slopes of the acute phase were 0.506%/s, and the maintenance phase was nearly flat (0.012%/s). The mean time at which the reaction changed from acute to maintenance phase was 7.4 s which is significantly different from RT (16.0 s). Mean dilation at this point (2.987%) was significantly different from MD (3.734%), but it was still 80% of MD in less than half of RT.

Conclusion: Bi-linear fitting parameters better characterises the arterial dilatory response than MD and RT. Further stratification of clinical groups using bi-linear fitting may provide insight of the underlying physiology of vessel dilation for different pathologies.