Systemic diseases are diseases that involve many organs or the whole body. Many of these diseases also affect the eyes. In fact, an eye exam sometimes leads to the first diagnosis of a systemic disease.

Why is the eye so important in systemic disease?

The eye is composed of many different types of tissue. This unique feature makes the eye susceptible to a wide variety of diseases as well as provides insights into many body systems. Almost any part of the eye can give important clues to the diagnosis of systemic diseases. Signs of a systemic disease may be evident on the outer surface of the eye (eyelids, conjunctiva and cornea), middle of the eye and at the back of the eye (retina).

The optic nerve and eye movements often reflect changes in the central nervous system. This is because a large part of the brain helps provide visual information and controls eye movements. Because the eye structures are uniquely transparent, a doctor can see inside the eye. The eye is the only organ in the body in which a doctor can directly see blood vessels. The health of the blood vessels in the eye often indicates the condition of the blood vessels (arteries and veins) throughout the body.