Poser doesn't have caustics, unfortunately.  Poser's refraction doesn't affect how an object, or more importantly a material, casts shadows.  it doesn't affect how an object, or materials, occlude ambient lighting (AO).  it doesn't affect how indirect lighting is calculated.  refraction only affects the surface shading of the material.  it doesn't really make light pass through the material.

when you have a material on an object you want to make clear and don't want to make the object invisible to raytracing or not cast shadows, you want to use transparency rather than refraction.