Old software by any company does not view well with the new HD monitors. If I remember correctly (not a safe bet), LR 5 was the first version to have readability options for the HD screens.
Most likely you need to update LR to 6.x.
Thanks, but what about element 14 which is not so old ?
Envoy? de mon iPad
Adobe lightroom 4 and element 14 font too small
Here's the answer:
Right click on the shortcut folder to the Lightroom or Adobe file that you're having issues with
Click on Properties
Click on Compatibility
Click on Override high DPI Scaling performed by....
Click on System