Rognidan and Vikruti Vigyan deals with the factors which are :

Essential to understand disease process as well as the diagnosis of disease.

The normal state of mind and body is called prakriti and the abnormal state of the mind and body is termed as Vikruti. Nidan Panchak is the base of diagnosis of disease.

The Knowledge gained by scrutinizing the causes and symptoms of a disease related to person is called Vikruti Vigyan.