Idiopathic intracranial hypertension (IIH) happens when high pressure around the brain causes symptoms like vision changes and headaches. “Idiopathic” means the cause isn’t known, “intracranial” means in the skull, and “hypertension” means high pressure. IIH happens when too much cerebrospinal fluid (CSF) — the fluid around the brain and spinal cord — builds up in your skull. This puts extra pressure on your brain and on the nerve in the back of your eye, called the optic nerve. If you notice changes in your vision, talk to your eye doctor. The doctor can figure out if your symptoms are related to IIH or another condition. If it’s IIH, there are treatments that can help with the symptoms.

Symptoms can include:

• Headaches
• Tinnitus (ringing in the ears)
• Temporary blindness
• Double vision
• Blind spots
• Neck and shoulder pain
• Peripheral (side) vision loss

If you notice any changes to your vision or other symptoms, talk to your eye doctor.

IIH is rare, but some people are at higher risk. It’s most common in women ages 20 to 50. Being overweight or obese also makes IIH more likely. You may be at higher risk if you have a body mass index (BMI) greater than 30, or if you recently gained weight. You can calculate your BMI using CDC’s online calculator.

Experts don’t know what causes IIH. But there are other types of intracranial hypertension that do have known causes:

• Acute intracranial hypertension happens suddenly, usually because of an accident or stroke
• Chronic intracranial hypertension develops over time, usually because of a health problem like a blood clot or brain tumor, or from taking certain medicines

If doctors can’t find a reason for the high pressure, it’s called IIH.

Your eye doctor will do several tests to check for signs of IIH, including a dilated eye exam to look at the back of your eye and a visual field test to check your peripheral vision.

Your eye doctor may also want you to see a neurologist (a doctor specializing in the brain). The neurologist will check to make sure your symptoms aren’t happening because of another health problem, like a brain tumor. The neurologist may do tests including:

• A physical exam
• Brain imaging, like a CT or MRI scan
• A spinal tap (lumbar puncture) to test your CSF

Researchers are studying what causes IIH, including how genes and hormones might play a role. In 2010, NEI funded a clinical trial to test the medicine acetazolamide (Diamox) in IIH patients with mild vision loss. This trial helped to prove that acetazolamide, along with a weight loss plan, can help to restore some vision in people with IIH. It also helped create clear guidelines for doctors on how to prescribe acetazolamide for patients with IIH.