Window glass material (Eevee) New to blender, got a question about window glass.

I have tried several examples but can't get it to do what I want.

The problem is that the background which I have set in the world settings is getting blurred when viewed through the glass material.

I have attached a screenshot. The selected object is a plane to which I have assigned the glass material. As you can see the background through the plane is being blurred.

I have no idea which setting is getting me this effect. 
I have tried a lot of sliders :-)

Hopefully someone can shed some light on this.



Edit:

I tried using IOR 1.0. Still the same issue.
Although when rendered with cycles (which I don't use on osx) the blur was gone.

So it seems to be an Eevee setting or issue.

Any idea what can affect this in Eevee?
The refraction algorithms in Eevee (which the glass shader uses either) lower resolution of everything behind refracted surface to speed up render and performance - this is what causes the bluriness. If you don't need a refraction distortion, the solution as it has been already mentioned is in using Principled BSDF. Increase "Metallic" all the way up to 1 and plug in Fresnel node into Alpha socket - you will get a fake glass material without lowering a background resolution. Anyway if you need a physically correct refraction I'm afraid the only way is to use Cycles.