Reproduction Steps:
1. Create new project
2. Create 3D object Sphere
3. Select Wireframe mode
4. Try dragging Unity window to the FullHD and back to Retina displays
5. Notice that wireframe thickness when on Retina display is relatively lower than on other display

Expected behaviour: Same thickness on both displays
Actual Results: Wireframes thickness on Retina screen is much lower

Reproduced in versions: Unity 5.4.0f3, 5.4.0p2, 5.5.0a6
Did not reproduced on Unity 5.2.4f1, 5.3.6p3