Keep annotated class in Proguard

I have a bunch of classes that use e.g. an @Singleton annotation like so

@Singleton
public class ImageCache

that I would like to keep. How can I configure a proguard -keep statement so it applies to all classes that have that annotation.

Btw in terms of context I need this for an app using Roboguice on Android, which is why I added the tags. Might help others.