{"id":3322,"date":"2026-04-13T19:26:19","date_gmt":"2026-04-13T17:26:19","guid":{"rendered":"https:\/\/www.first-sight.ch\/?post_type=glossary&#038;p=3322"},"modified":"2026-04-13T19:27:35","modified_gmt":"2026-04-13T17:27:35","slug":"anisocoria-and-horner-syndrome","status":"publish","type":"glossary","link":"https:\/\/www.first-sight.ch\/en\/glossar\/anisocoria-and-horner-syndrome\/","title":{"rendered":"Anisocoria and Horner Syndrome"},"content":{"rendered":"<p>Anisocoria refers to a condition in which the pupils of both eyes are different sizes. A small difference in size is normal in up to 30% of the population (physiological anisocoria). However, a larger, fluctuating, or newly occurring difference may indicate an eye or neurological disorder and should be evaluated by an ophthalmologist.<\/p>\n<h2>How does the pupil work?<\/h2>\n<p>The iris, the colored ring of the eye, surrounds the pupil, the central opening through which light enters the eye. Two muscle systems in the iris regulate pupil width:<\/p>\n<p>In bright light, the pupil constricts (miosis) to let in less light. In darkness, it dilates (mydriasis) to take in as much light as possible.<\/p>\n<p>Normally, both pupils respond simultaneously and symmetrically.<\/p>\n<h2>When is anisocoria worth investigating?<\/h2>\n<p>The ophthalmologist pays attention to which lighting situation makes the difference more pronounced:<\/p>\n<ul>\n<li><strong>Difference larger in darkness:<\/strong> The smaller pupil is suspicious, it does not dilate sufficiently. This can indicate Horner syndrome.<\/li>\n<li><strong>Difference larger in bright light:<\/strong> The larger pupil is notable, it does not constrict properly. Causes can include cranial nerve palsy, Adie syndrome, or trauma.<\/li>\n<\/ul>\n<p>In physiological anisocoria, the size difference (usually less than 1 mm) remains the same in all lighting conditions.<\/p>\n<h2>Causes of an unusually large pupil<\/h2>\n<ul>\n<li><strong>Eye injury:<\/strong> Damage to the iris can permanently dilate the pupil.<\/li>\n<li><strong>Medications:<\/strong> Certain eye drops, nasal sprays, or transdermal patches can accidentally dilate a pupil. Inform your doctor about all medications used.<\/li>\n<li><strong>Adie syndrome (tonic pupil):<\/strong> The pupil reacts slowly and incompletely to light. Often reflexes are also diminished and near accommodation is impaired.<\/li>\n<li><strong>Oculomotor nerve palsy (third cranial nerve palsy):<\/strong> A dilated pupil together with a drooping upper eyelid and double vision can indicate a serious cause and must be investigated urgently.<\/li>\n<\/ul>\n<h2>Causes of an unusually small pupil<\/h2>\n<ul>\n<li><strong>Eye inflammation (iritis):<\/strong> Inflammatory adhesions can narrow the pupil.<\/li>\n<li><strong>Horner syndrome:<\/strong> Damage to the sympathetic nerve pathways leads to a small pupil on the affected side.<\/li>\n<\/ul>\n<h2>What is Horner syndrome?<\/h2>\n<p>In Horner syndrome, the sympathetic nerves that run from the brain through the neck and chest to the eye are damaged. The typical signs are:<\/p>\n<ul>\n<li><strong>Miosis:<\/strong> The affected pupil is smaller and dilates slowly in darkness.<\/li>\n<li><strong>Ptosis:<\/strong> The upper eyelid hangs slightly, sometimes the lower eyelid is also slightly elevated \u2013 overall the eye appears smaller.<\/li>\n<li><strong>Heterochromia:<\/strong> If Horner syndrome occurs in the first year of life, the iris of the affected side can remain lighter than the other.<\/li>\n<li><strong>Occasionally:<\/strong> reduced sweating and less skin redness on the affected face side.<\/li>\n<\/ul>\n<h2>Causes of Horner syndrome in children<\/h2>\n<p>Horner syndrome in children can be congenital or acquired:<\/p>\n<ul>\n<li><strong>Congenital:<\/strong> Often caused by birth injuries to the neck or shoulder. In many cases the cause remains unclear.<\/li>\n<li><strong>Acquired:<\/strong> Possible from neck injuries, neck surgery, or tumors in the chest, neck, or brain. In children, neuroblastoma must be ruled out in particular \u2013 a tumor that can affect the sympathetic nerves.<\/li>\n<\/ul>\n<h2>Diagnosis<\/h2>\n<p>If Horner syndrome is suspected, the <a href=\"https:\/\/www.first-sight.ch\/en\/\">ophthalmologist<\/a> first performs a thorough examination, checking pupil reactions, eyelid position, and eye movements. Special eye drops (pharmacological testing) can confirm the diagnosis. Depending on the suspicion, imaging procedures (CT or MRI of the head, neck, and chest) and urine tests are then arranged to rule out an underlying cause \u2013 particularly a tumor.<\/p>\n<h2>When should you see an ophthalmologist?<\/h2>\n<p>If you notice pupils of different sizes in your child If an eyelid suddenly droops If double vision occurs If a pupil change is noticed after an injury<\/p>\n<p>Timely evaluation provides clarity and enables early treatment if necessary.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Anisocoria refers to a condition in which the pupils of both eyes are different sizes. A small difference in size is normal in up to 30% of the population (physiological anisocoria). However, a larger, fluctuating, or newly occurring difference may indicate an eye or neurological disorder and should be evaluated by an ophthalmologist. How does [&hellip;]<\/p>\n","protected":false},"featured_media":0,"template":"","meta":{"_acf_changed":false,"_wpce_doc":"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