This looks like a useful program for this type of image. I would like to modify your suggestion Rosemaryr, in the new layer that has the caustic surface, I would recommend using the Perspective option from the Transform tool and slant the image a little to give a sense of depth. You would have to expand beyond the outer edges of the image area to do this but I think it would be effective.

Sorry if I am not making myself clear. It is easier to show than to say.

Yoshi