I don’t really know what is wrong with this, but I am guessing the “issue” you are facing is caused by one of these:
First of all, you are in material preview mode, which causes all the shading to be very low quality for faster rendering. Switch to Renderingmode to get a more accurate image of your scene.
Secondly, if what you mean with quality drop is those jagged lines around the eyes, the issue is probably a bump map which is being applied to your objects material. To disable this, or at least turn down the strength a bit, all you need to do is:
Now your node-screen should look something like this. Find the “Bumb” node and turn down the strength a little, until you are pleased with the result. Alternatively, you could remove the bumb completely, but I would not recommend this, as it would make the texture look very flat.