INTRODUCTION AND DEFINITION
The tonic pupil, sometimes called Adie's tonic pupil or simply the Adie pupil, is the term used to denote a pupil with parasympathetic denervation that constricts poorly to light but reacts better to accommodation (near response), such that the initially larger Adie pupil becomes smaller than its normal fellow and remains tonically constricted, redilating very slowly when exposed to dark.
Although the eponym credits Adie with its discovery , the tonic pupil was originally described nearly synchronously by Adie, Morgan, Symonds, and Holmes in 1931 [2-5].
The tonic pupil is a common cause of anisocoria, or unequal pupils. The prevalence of the Adie's pupil is about two cases per 1000 population. Although patients of all ages are affected, the mean age is 32 years, and there is a female predominance (2.6:1) for the idiopathic variety (Adie's tonic pupil).
The tonic pupil is the result of damage to the parasympathetic ciliary ganglion. The parasympathetic innervation to the iris and ciliary body travels with the third cranial nerve and synapses in the ciliary ganglion. After damage to the ciliary ganglion, reinnervation and up-regulation of the post-synaptic receptors occurs, a process known as denervation supersensitivity. The number of axons destined for the ciliary body, however, is about 30 times the number that supply the pupil. After denervation occurs, the reinnervation may be aberrant, and fibers formerly destined for the ciliary body now travel to the pupil (aberrant regeneration).
Activation of the near response in this situation produces a better near reaction than light reaction (light-near dissociation of the pupils), and the reaction is tonic.