No you do not need the Infinite Screen Extension for The Division. All features in The Division are integrated into the game. The Infinite Screen feature that was present in the game during the beta was not deemed to be good enough for release but it will be added in an upcoming patch which shouldn’t be too far off.
The issues you’re describing sounds a lot like a DPI related problem that we’ve recently discovered. If the DPI in Windows is set to anything else than 100% then the eye tracking features won’t work properly when playing at resolutions lower than that of the monitors native resolution. Either set the DPI to 100% or change the in game resolution to match the monitors native resolution and see if that helps. A bugfix for this issue is in the works.
(Note: If you’re on a 4k monitor then Windows sets the DPI to 150% by default!)
You can change the DPI by opening “Display Settings” and then drag the slider called “Change the size of text, apps and other items:”
Hope it helps.