An electron-optical system for inspecting or reviewing an edge portion of a sample includes an electron beam source configured to generate one or more electron beams, a sample stage configured to secure the sample and an electron-optical column including a set of electron-optical elements configured to direct at least a portion of the one or more electron beams onto an edge portion of the sample. The system also includes a sample position reference device disposed about the sample and a guard ring device disposed between the edge of the sample and the sample position reference device to compensate for one or more fringe fields. One or more characteristics of the guard ring device are adjustable. The system also includes a detector assembly configured to detect electrons emanating from the surface of the sample.