Eyes of a 34 year old woman with Adie's syndrome. This is a neurological disorder that causes one pupil to be larger than the other, in this case it is the patient's right pupil. It also causes the slow constriction of the pupil in bright light and the loss of deep tendon reflexes, such as the knee jerk reaction. The cause of Adie's syndrome is not known, although it is thought to be due to either an infection or autoimmune disease affecting the areas of the brain responsible for eye movement (ciliary ganglion) and autonomic nervous system response (spinal ganglion).