The sympathetic fibres then travel with the trigeminal nerve through the superior orbital fissure to the ciliary muscle. Postsynaptic neurons travel down all the way through the brain stem on each side and finally exit through the cervical sympathetic chain, travel over the lung apices, and ascend to the superior cervical ganglia with the carotid artery, then onwards as a plexus around the internal carotid artery, passing through the cavernous sinus. The sympathetic input then comes from the hypothalamus with the first synapse at the ciliospinal centre at C8-T1 level. During sleep the pupils are partially constricted but still react to light. The pathway begins in the cortex, which exerts a modulatory effect on constriction which is lost during drowsiness and sleep but increased during intense concentration and arousal. Pupillary dilatation is controlled by the sympathetic system and is efferent only. Short ciliary nerves then innervate the iris sphincter and muscles of accommodation. They travel in the superficial part of the oculomotor nerve via the cavernous sinus and the superior orbital fissure to synapse in the ciliary ganglia. From each Edinger-Westphal nucleus, preganglionic parasympathetic fibres exit with the oculomotor nerve. Each pretectal nucleus has two pupillary motor outputs, one to the Edinger-Westphal nucleus on its own side and one to the other side. ![]() ![]() The efferent limb for pupillary constriction comes from the pretectal nucleus via the Edinger-Westphal nucleus (also in the midbrain) to the ciliary sphincter muscle of the iris. The afferent limb is made up of the retina, the optic nerve and the pretectal nucleus in the midbrain, all on the same side. For physiologic anisocoria, no treatment is needed.The pathway for pupillary constriction for each eye has an afferent limb taking sensory information to the midbrain, and two efferent limbs (one to each eye). Treatment depends on identifying and addressing the underlying problem. Neuroimaging with MRI (occasionally CT) depending on the person’s history and what is found on neuro-ophthalmic and neurologic examinations. Taking a careful history of symptoms, noting when they started and what other problems may be present.Ĭhecking the ability of each pupil to constrict in the presence of bright light and to dilate in the darkness. If the problem is new, the doctor will then focus on which pupil is responding differently. When a doctor sees a patient for uneven pupil size, the first concern is to determine whether the unevenness is new or long-standing. Reaction to certain topical dilating medications (such as a pet’s eye drops, or anti-nausea or motion sickness patches such as scopolamine) that may accidentally get into one eye. This may be due to a brain aneurysm, and should be urgently evaluated in the emergency room. On the other hand, a person whose pupils are uneven when they were normal before may be experiencing a serious problem such as:Ī torn or blocked blood vessel in the neck (usually the result of head or neck trauma), which could cause a mildly droopy eyelid on the side of the smaller pupil.Ī third nerve palsy can result in the inability to move the affected eye normally, in addition to eyelid drooping (which is often significant) on the side of the larger pupil. In these cases, there are no other symptoms and both of the person’s pupils react to changes in light. This is called “physiologic anisocoria” and is normal. Slight differences between the two pupils may be present in up to 20 percent of people. This is to rule out eye conditions such as acute angle closure glaucoma or inflammation of the front part of the eye (uveitis or iritis). ![]() More often than not, it is pointed out to the person by someone close to them.Īn ophthalmologist should be seen to rule out ocular causes of eye pain and pupil asymmetry, especially when vision loss or changes, redness or discharge from the eye(s) is present. Uneven pupil size may be noticed by the person or by a health professional during an examination.
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