What area of medicine would focus on adult diseases?

The field of medicine that primarily focuses on adult diseases is internal medicine. Specialists in internal medicine, known as internists, are trained to diagnose, treat, and manage a wide range of health issues that affect adults. They emphasize a comprehensive understanding of the body's systems and the various chronic and complex conditions that can arise in adulthood, such as diabetes, hypertension, cardiovascular disease, and pulmonary issues.

This specialty also involves a holistic approach to patient care, where internists consider the patient’s overall health, lifestyle, and prevention strategies, which is particularly important in managing diseases prevalent in adults.

Other medical fields such as ophthalmology, radiology, and toxicology have different focal points: ophthalmology concerns eye health, radiology involves imaging technologies for diagnosis, and toxicology studies the effects of toxins and drugs on the body. Thus, their primary focus is not on adult diseases in the comprehensive manner that internal medicine is.