Both Nikon D810A and Sony A7R have 36.0 MP resolution sensors but Nikon D810A's sensor is Full frame (35.9 x 24 mm ) and Sony A7R's sensor is Full frame (35.9 x 24 mm ).
Since Sony A7R's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon D810A.
One other difference between these two cameras that is worth mentioning is that Sony A7R's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the D810A and A7R sensor size comparison.
Nikon D810A and Sony A7R have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.