It can be assessed by viewing the pupils through several cycles of light and dark stimulation. The sympathetic fibers serve to dilate the pupil under conditions of dark or in response to psychosensory stimulation (ie, startle or pain).ĭilation lag refers to the slowed dilation of the affected pupil in response to dark. Ptosis typically measures 1-2 mm miosis often measures less than 2 mm and is greatest in the dark. The sympathetic nerve pathway has 3 divisions: first order (hypothalamus to C8-T1), second order (C8-T1 to superior cervical ganglia), and third order (superior cervical ganglia to the pupil dilators and lid). The sudomotor sweat fibers supplying the face exit onto the external carotid and its branches. The sympathetic pathway begins in the hypothalamus, travels down the brain stem (where it is most often disrupted in the lateral medulla), through the cervical spinal cord to the level of the ciliospinal center of Budge-Waller at C8-T1, then over the lung apex, ultimately ascending with the carotid artery into the cavernous sinus to the pupil dilators and the Muller muscle of the lid. The causes vary from life-threatening to benign conditions.
Features include ptosis, miosis, and anhidrosis however, the exact presentation varies with the site of the lesion. In the English-language literature, Horner syndrome refers to sympathetic paresis that affects the eye. Two conditions produce normally reactive pupils with anisocoria greater in darkness: Horner syndrome and physiologic anisocoria. See the diagram below.įlowchart to assist in the diagnosis of anisocoria (modified with permission from Thompson and Pilley)įor specific discussions of several of these topics, see the articles Oculomotor Nerve Palsy and Horner Syndrome. The causes of anisocoria are diverse and varied refer to the following flowchart to deduce the specific cause. Has been reported to occur with the use of pharmacological agents such as propofol during general anesthesia. Transient anisocoria reflects benign causes such as migraine headache, and can represent transient parasympathetic or sympathetic dysfunction from other causes. Mechanical damage to the iris from trauma, surgical intervention, or inflammation or the effects of uveitis may produce anisocoria. Proptosis may suggest the presence of a space-occupying lesion within the orbit. The presence of pain may be associated with an expanding or ruptured intracranial aneurysm causing a compressive third nerve palsy or carotid dissections but is also typical of microvascular ocular motor neuropathies. Pupil reactivity is graded subjectively on a scale of 0 to 4, to allow quantification of asymmetry.Īssociated features are often key to the diagnosis.ĭiplopia and ptosis may indicate the presence of a third nerve palsy.
Physical examination of pupil size in light, pupil size in the dark, pupil reactivity to light and dark help to localize the problem. The pupil size difference itself seldom produces symptoms. Several causes of anisocoria are life threatening, including Horner syndrome due to carotid dissection or third nerve palsy due to aneurysmal expansion or rupture. The parasympathetic system constricts the iris, while sympathetic channels dilate the iris.Īnisocoria is common, with an estimated prevalence of 20% of the normal population. Pupil size depends upon the effects of the autonomic nervous system and the iris muscle. The differential diagnosis of a large pupil that is poorly reactive to light includes: a palsy of the third cranial nerve, pharmacologic mydriasis, and a tonic pupil.Ī tonic pupil refers to a pupil with parasympathetic denervation and a results in a pupil that is poorly reactive to light but strongly reactive to a near target: see with infection as with herpes zoster, orbital surgery, or systemic autonomic neuropathies, but also seen idiopathically as Adie tonic pupil.Ĭan be associated with severe and life-threatening neurologic conditions such as a cerebral herniation, intracranial mass or acute intracranial hemorrhage, Horner syndrome and other space occupying lesions that compress the cranial nerves. If anisocoria courier is greater in bright light conditions, the abnormal pupil is the larger pupil. If anisocoria is greater in dim lighting conditions, the abnormal pupil is the smaller pupil since it is unable to fully dilate, and implyies a problem with the sympathetic pathway which innovates the iris dilator muscle. When associated with neurologic symptoms such as ptosis or diplopia it may be an indication of dysfunction of the third cranial nerve which is vulnerable to compression from aneurysms and other lesions. The presence of unequal pupil size may be a sign of a serious underlying neurologic condition, and requires careful attention. Refers to unequal pupil sizes, is a common condition.Ĭauses range from life threatening to completely benign.
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