Score as normal.
Be careful about putting too much pressure when scorning as, in general, opalescent glass does not make as much sound when being scored as transparent glasses do.
The difficulty with opalescent glass is seeing where the score is when you turn the glass over.
If you are using a piece of glass not much larger than the circle you are cutting, you can place the fingers of your hand over the score line and your thumb on the back as you lift the glass to turn it over. This gives you the location to begin the pressure to run the score. As the first part of the score runs, you will be able to follow the leading edge of the opening score around the circle.