Unit 3: Pupil Abnormalities, Facial Nerve Palsy & Ptosis

In the acute stage a tonic pupil is abnormally large with poor reaction to light and there is reduced accommodation.

The characteristic abnormality is a "tonic" near response manifesting as delayed mydraisis with reversal of the near response (i.e. when fixating a far target after fixating a near target).

Because the near response is better than the light response, tonic pupil is one cause of pupillary light-near dissociation.

There are many causes of tonic pupils including autonomic neuropathy, in which it is usually bilateral.

The commonest cause is the idiopathic benign Adie (or Holmes-Adie) syndrome, in which deep tendon reflexes are absent. Due to re-innervation accommodation recovers after a few weeks and over a longer time period the pupil usually becomes abnormally small.

• Examination shows right pupil is smaller than the left in the light.
• Degree of anisocoria is about the same in the dark.
• A Horner's pupil will result in anisocoria that is greater in the dark than in the light (abnormal pupil is the smaller one).
• An acute tonic pupil will result in anisocoria that is greater in the light than in the dark (abnormal pupil is the larger one).