With Slicer 4.10.0 and the transition to Qt5, there is greatly improved scaling of widgets for higher DPI monitors (I know a user with a 4K monitor), however various icons in those scaled widgets now appear blurry. Icons that are primarily rectangular shapes scale well, but anything that has curves or is angled now looks blurry. A likely issue is the usage of the png format for the icons which doesn’t scale well.
It appears that icons such as the markups place fiducial png or any of the other icons in the toolbar such as segment editor png are pngs that are 21x21px in size. Even the 3D Slicer logo at the heading above all modules in the left side bar area appears blurry.
The slice offset text in the slice windows also appears smaller relative to the space it occupies in the colored header of the individual slice window.