The parasympathetic supply to the iris sphincter muscle consists of a 2-neuron pathway. Diabetes mellitus or inflammation may damage outflow from the ciliary ganglion, causing a type of pupillary abnormality known as a tonic pupil. Local trauma to the iris sphincter muscle may result in mechanical restriction of pupillary movement. If the efferent limb is damaged asymmetrically, anisocoria will result ( 47).įor example, a stroke in the dorsolateral medulla may injure the central neuron of the oculosympathetic pathway to cause ipsilateral miosis and poor pupillary dilation (Horner syndrome) usually in association with other neurologic symptoms and signs. The parasympathetic component innervates the iris sphincter muscle the sympathetic component innervates the iris dilator muscle. The efferent limb has two parts: parasympathetic and sympathetic. If the afferent limb is damaged asymmetrically, it will result in a relative afferent pupillary defect. The pupillary innervation pathway consists of an afferent and an efferent limb. He declined a CT angiogram, so MRI/MR angiography was performed, showing a left internal carotid artery dissection.Īny process that affects the autonomic innervation of the iris muscles or damages the iris muscles themselves will cause a pupil abnormality. Because of the combination of new headache and Horner syndrome, the diagnosis of cervical carotid dissection was made presumptively, and the patient was sent for urgent imaging. He had not noticed the ptosis and neither had several physicians in earlier examinations. Instillation of topical apraclonidine 0.5% in both eyes produced reversal of the anisocoria, confirming a diagnosis of left Horner syndrome. Both pupils constricted normally to light, but the left pupil dilated relatively slowly when light was withdrawn (“positive dilation lag”). Neuro-ophthalmologic examination showed 1 mm of left upper lid ptosis, a miotic left pupil, and anisocoria that worsened in the dark. Platelet count, erythrocyte sedimentation rate, and C-reactive protein were within normal limits. He had no other giant cell arteritis symptoms. A 68-year-old man with new headache was referred to the emergency eye clinic from the general emergency department to rule out giant cell arteritis. Prognosis and complications are individually assessed for the specific pupillary abnormality and its etiology. Because the parasympathetic system innervates the ciliary muscle, which governs accommodation, as well as the iris sphincter muscle, which governs pupil size, patients with oculomotor nerve palsy or short ciliary nerve damage may report blurred near vision while reading. Occasionally, patients may complain of photophobia in the eye with a large (mydriatic) pupil because increased light reaches the retina through the wider aperture. Often pupillary abnormalities are asymptomatic or noticed only by an observer. The abnormality may be transient or constant. Abnormally positioned pupil (corectopia)
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