Diagnosis

In addition to a general medical examination, your doctor will conduct tests to judge the nature of your symptoms and identify a possible cause.

Tests to confirm Horner syndrome

Your doctor may be able to diagnose Horner syndrome based on your history and his or her assessment of your symptoms.

Your doctor, often an ophthalmologist, may also confirm a diagnosis by putting a drop in both eyes — either a drop that will dilate the pupil of a healthy eye or a drop that will constrict the pupil in a healthy eye. By comparing the reactions in the healthy eye with that of the suspect eye, your doctor can determine whether nerve damage is the cause of problems in the suspect eye.

Tests to identify the site of nerve damage

The prominence or nature of certain symptoms may help your doctor narrow the search for the cause of Horner syndrome. Your doctor may also conduct additional tests or order imaging tests to locate the lesion or abnormality disrupting the nerve pathway.

Your doctor may administer a type of eyedrop that will cause significant dilation of the healthy eye and little dilation of the affected eye if Horner syndrome is caused by a third-order neuron abnormality — a disruption somewhere in the neck or above.

Your doctor may order one or more of the following imaging tests to locate the site of a probable abnormality causing Horner syndrome:

• Magnetic resonance imaging (MRI), a technology that uses radio waves and a magnetic field to produce detailed images
• Carotid ultrasound
• Chest X-ray
• Computerized tomography (CT), a specialized X-ray technology
• X-ray imaging