A dilated, poorly reactive pupil may occur as part of the ocular ischemic syndrome, a condition that most commonly affects patients who have severe carotid artery stenosis associated with poor collateral circulation to the eye (5). Other disorders that can cause chronic ocular ischemia include ophthalmic artery occlusion, carotid-cavernous fistula, giant cell arteritis, and rarely following neurosurgical clipping of an anterior communicating artery aneurysm. In these settings, an efferent pupil defect is caused by ischemia affecting the iris, as well as the suprachoroidal short ciliary nerves if sufficient posterior segment ischemia additionally exists. Iris neovascularization may be present, especially in long-standing cases.
Traumatic iridoplegia describes the large pupil that is nonreactive to both light and accommodation that occurs following blunt trauma to the globe. If the iris itself is directly injured or torn, then it will not constrict in response to a topically applied direct cholinergic agonist. Conversely, if the mydriasis results solely from injury of the short ciliary nerves, either in the anterior ocular segment (e.g., rupture of branches supplying the iris due to anterior chamber angle recession) or in the posterior ocular segment (e.g., traction of suprachoroidal nerves due to choroidal rupture), then the pupil will constrict in response to a cholinergic agonist. Aberrant regeneration of the intraocular muscles can occur following injury to the short ciliary nerves, resulting in a posttraumatic tonic pupil.
A common cause of damage to the intraocular parasympathetic fibers results from laser treatment to the retina for diabetic retinopathy or during laser trabeculoplasty to treat glaucoma. Given that the ocular segment of the postganglionic short ciliary nerves travel within the subchoroidal space, between the retina and sclera, they are susceptible to thermal injury during therapeutic laser application. Findings typical of a tonic pupil, including cholinergic supersensitivity of the iris sphincter, can develop following panretinal photocoagulation (142).