Pathological changes that occur in neurodegenerative diseases of the brain can often also be detected in the retina. Therefore, the idea of using the retina as a so-called “window to the brain” has existed for some time. Whether parallel pathophysiological mechanisms of the retinal and cerebral vascular bed exist in the acute phase after subarachnoid hemorrhage (SAH) is not yet known. With dynamic retinal vessel analysis, a new non-invasive tool exists to measure retinal vessel diameters comparatively easily. This tool is used in this study to assess the reactivity to hypercapnia of the retinal vessels, while simultaneously measuring cerebral blood flow to assess the hypercapnia activity of the cerebral vessels. To use the dynamic retinal vessel analysis repetitively over six hours, it first had to be successfully established in the rat. Using two different anesthetic protocols (isoflurane and ketamine/xylazine), a subarachnoid hemorrhage was induced in male Wistar rats by injecting 0.5 mL of blood into the cisterna magna. Subsequently, cerebral blood flow was continuously recorded by laser speckle contrast analysis for six hours after SAB. Measurement of retinal vessel diameter using dynamic retinal vessel analysis was performed during the hypercapnia phases, 30 min, 60 min, 120 min, 240 min, and 360 min after SAB. Results show that in the isoflurane group cerebral and retinal hypercapnia activity is impaired up to 240 min after SAB, while in the ketamine/xylazine group, cerebral reactivity is impaired up to 120 min after SAB, and retinal hypercapnia activity remains impaired even up to six hours after SAB. Overall, the simultaneous measurement of cerebral blood flow and retinal vessel diameter up to six hours after SAB was successfully established. The study further provides detailed information on the course of the disturbance of hypercapnia activity in the retinal and cerebral vessels in the acute phase up to six hours after SAB. Thus, it contributes to the verification of the applicability of the retina as a window to the brain. Further research is needed to verify the correlation and further extent of impaired hypercapnia activity.
