The Manifold Walk option in PxrUnified makes use of a technique to generate caustics that can be less expensive than generating photons through the scene. You can also fine tune what is and isn't a receiving or caustic generating material. This is especially useful for eyes in VFX and Feature Animation work. You can selectively have the cornea trace caustics onto the iris of the eye adding realism and beauty. You can also better illuminate objects realistically behind or inside transmissive objects.

Below we go over the steps in a simple scene for using the Manifold Walk.

In the example below we have a simple ground plane and a glass cylinder. The ground plane is diffuse and the cylinder is glass. The default render using Thin Shadows produces this result: