Effects of Change in Blood Pressure on Retinal Capillary Rarefaction in Patients With Arterial Hypertension

Change in retinal vessel density after achieving blood pressure treatment target (OCT-A).

As OCT devices are able to calculate the movements of erythrocytes, retinal perfusion can be visualized with Optical Coherence Tomography Angiography. No contrast media is necessary for the representation of retinal vessels.

Change in choroidal vascularity index after achieving blood pressure treatment target (EDI-OCT).

The choroid will be imaged with the enhanced-depth-imaging-OCT (EDI-OCT) (Spectralis, Heidelberg Engineering, Heidelberg, Germany). By using an automatic detection algorithm, developed by Tian et al., the choroid will be separated from the sclera and Bruch´s membrane. Afterwards, the image will be binarized using the software Fiji ImageJ. An autolocal threshold will be applied and the image will be converted into an RGB (red, green, blue) image, thereby determining the luminal area of the choroid. The choroidal vascularity index is obtained by dividing the luminal area by the total choroidal area.

Change in neurovascular coupling after achieving blood pressure treatment target (DVA).

The DVA allows for the real time measurement of retinal vessel diameters in vivo. The DVA is a commercially available system (IMEDOS, Jena, Germany) which comprises a fundus camera, a video camera, a real time monitor and a personal computer with an analyzing software for the accurate determination of retinal arterial and venous diameters. Every second a maximum of 25 readings of vessel diameter can be obtained. For this purpose the fundus is imaged onto the charge coupled device chip of the video camera. The consecutive fundus images are digitized using a frame grabber. In addition, the fundus image can be inspected on the real time monitor and, if necessary, stored on a video recorder. Evaluation of the retinal vessel diameters can either be done online or offline from the recorded video tapes.

Change in retinal oxygen saturation after achieving blood pressure treatment target (DVA).

Retinal oxygen saturation measurement is based on the image analysis by the oxygen module of the commercially available Dynamic Vessel Analyzer (DVA, Imedos, Germany). Two monochromatic fundus images are recorded by the retinal oximeter. In an image, obtained by the camera and filter assembly, the operator has to mark the vessel of interest by a mouse click. The vessel is traced automatically applying the following procedure. The vessel walls are located as photometric edges in the vicinity of the mouse cursor in the green channel image. If edges are determined, the search is continued in their proximity.

Change in ocular blood flow after achieving blood pressure treatment target (LSFG).

A commercially available LSFG (Nidek, Japan) system will be used in the present study. The LSFG device consists of a fundus camera equipped with a diode laser with a wavelength of 830 nm and a charge-coupled device. NB, the relative velocity of blood flow, is derived from the pattern of speckle contrast produced by the interference of a laser scattered by blood cells moving in the ocular fundus. Images are acquired continuously at the rate of 30 frames per seconds in a 4-second time period and stored on a personal computer. Equipped analysis software synchronizes the captured MBR images in each cardiac cycle, and averages the MBR in each heartbeat to produce a heartbeat map of the ONH and the retina/choroid.