For definition caustics are:
When light refracts through or reflects off of a surface, these bent rays are focused together, creating a bright pattern referred to as a caustic.(SolidWorks help).
In addition to reflective and refractive, there are two other types of caustics:
Caustics created by indirect lighting (scene illumination).
Indirect refractive caustics are always on in SolidWorks.
Indirect reflective caustics are always off in SolidWorks.
Caustics created by direct lighting, including spot or point lights.
Directional lights do not affect direct or indirect caustics.
Direct caustics are only visible when reflected off a floor appearance or real geometry.
In SolidWorks 2010 and previous versions wich use Photoworks (LightWorks engine), this option was found in: Photoworks options, Illumination tab
From SolidWorks 2011 and future versions, now Photoview (Nexus engine), this option is found in: Photoview options, direct caustics.