Tests and diagnosisBy Mayo Clinic staff
To diagnose Horner syndrome, your doctor will start by asking about your medical history and doing a complete physical examination.
Pupil dilation test
If you have Horner syndrome, your pupil will open (dilate) slower than normal. Your doctor may evaluate this by placing drops of medication in your eye that force your pupil to dilate. The way the pupil responds to the eye drops will help confirm or deny a diagnosis of Horner syndrome. If Horner syndrome is confirmed, such testing may help determine where the location of the problem in the sympathetic pathway is located. This testing is often done by an eye doctor (ophthalmologist).
A physical exam and pupil dilation test can confirm a diagnosis of Horner syndrome. However, to find the underlying cause of Horner syndrome you'll likely need other tests. Depending on your situation, these may include:
- X-rays of your chest to look for a tumor or other condition that may be affecting the sympathetic nerves of your face.
- Magnetic resonance imaging (MRI) of your head, neck and chest to identify tumors, signs of stroke, carotid artery dissection and other conditions that may affect the sympathetic nerves of your face.
- Blood tests or urine tests.
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