Principles behind practice. 6. Disease causation. The role of epidemiological evidence.

How can epidemiology contribute to understanding the cause of clinical disease? We discuss the nature of causality and the intrinsic limitations of all empirical science, including epidemiology, in establishing "proof" of causality. Our examples relate to eye disease: How the cause of blindness from retrolental fibroplasia was unravelled. How the congenital rubella syndrome was discovered as a cause of congenital cataract. How allopurinol was cleared from suspicion as a cause of cataract.