Characterizing 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 provocation appears to be biphasic. The vessel diameter rapidly increases (acute-phase) over 5-10s, then barely increases thereafter (maintenance-phase) until flicker-light cessation. This reaction is usually characterised at a single point by two parameters: maximum-dilation relative to baseline diameter (MD,%) and time to maximum-dilation (RT,s). This paper describes the biphasic reaction of retinal arteries during flicker-light 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 flicker-light provocation was characterized 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 7.4s which is significantly different from RT (16.0s). 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 bilinear fitting may provide insight of the underlying physiology of vessel dilation for different pathologies.