I found this on the Internets:
Unfortunately, they made the decision in Windows 8.1 to try to ‘improve’ the scaling of fonts, but this doesn’t really work, so you need to turn that feature off.
To do this, right click on your desktop and choose Screen Resolution, then click ‘Make text and other items larger or smaller’, then check the box alongside ‘Let me choose one scaling level for all my displays’ and boom, problem solved. You’ll notice all of your apps will return to their former glory, before the Windows 8.1 update.
May or may not be relevant, I don’t know, but worth a try perhaps.