Modelling Lenses in Optix

Hello,

currently I’m trying to get from a sphere to a lense in my OptiX-project.
Are there maybe examples of lenses, maybe in form of .cu-files, in the SDK for OptiX newer than 3.9.1, I could use?
Or is there any recommended way for implementing in intersection and bounding box programs for a certain geometry?

Thank you,
Dennis