Adie syndrome is is a neurological disorder affecting the pupil of the eye and the autonomic nervous system. It is characterized by one eye with a pupil that is larger than normal that constricts slowly in bright light (tonic pupil), along with the absence of deep tendon reflexes, usually in the Achilles tendon. In most cases, the cause of Adie syndrome is unknown. Some cases may result from trauma, surgery, lack of blood flow, or infection. Treatment may not be necessary. Glasses and eye drops may help when treatmend is needed.

The term Adie syndrome is used when both the pupil and deep tendon reflexes are affected. When only the pupil is affected, the disorder may be referred to as Adie's pupil. 

In most cases, the cause of Adie syndrome is unknown (idiopathic). The tonic pupil in Adie syndrome is believed to result from inflammation or damage to the ciliary ganglion (a cluster of nerve cells found behind the eye) or damage to the post-ganglionic nerves. The ciliary ganglion is part of the parasympathetic nervous system, a component of the autonomic nervous system. It helps control the pupil's response to light and other stimuli. In most cases, damage to the ciliary ganglion or post-ganglionic nerves is caused by an infection. Damage may also result from autoimmune processes, tumors, trauma, and complications of surgery.  

The loss of deep tendon reflexes in Adie syndrome is believed to be caused by damage to the dorsal root ganglion, a cluster of nerve cells in the root of the spinal nerves.

In rare cases, Adie syndrome may be inherited. In these cases, it appears to follow an autosomal dominant pattern of inheritance. 
  

Adie syndrome is characterized by one eye with a pupil that is larger than normal that constricts slowly in bright light (tonic pupil), along with the absence of deep tendon reflexes, usually in the Achilles tendon. It typically begins gradually in one eye, and often progresses to involve the other eye. At first, it may only cause the loss of deep tendon reflexes on one side of the body, but then progress to the other side. The eye and reflex symptoms may not appear at the same time. People with Adie syndrome may also sweat excessively, sometimes only on one side of the body. The combination of these 3 symptoms – abnormal pupil size, loss of deep tendon reflexes, and excessive sweating – is usually called Ross’s syndrome, although some doctors will still diagnosis the condition as a variant of Adie syndrome. Some individuals will also have cardiovascular abnormalities. The symptoms of Adie syndrome can appear on their own, or in association with other diseases of the nervous system, such as Sjogren syndrome or migraine.