context: When you have optic neuritis, the nerve that sends messages from your eye to your brain, called the optic nerve, is inflamed. It can happen all of a sudden. Your vision gets dim or blurry. You can't see colors. Your eyes hurt when you move them. It's a common problem for people living with multiple sclerosis ( MS). The symptoms can seem scary, but most people recover fully, often without treatment. We don't know why, but sometimes your immune system attacks the fatty coating called myelin that covers and protects your optic nerve. When the myelin is damaged or missing, your optic nerve can't send the right signals to your brain. This can lead to changes in your vision. Optic neuritis is one of the most common symptoms of the relapsing-remitting form of MS. But it can also happen when you take certain medications or if you have diabetes. It's also linked to neuromyelitis optica ( NMO), or Devic's disease. This autoimmune disorder causes immune system cells and antibodies to attack your optic nerves, spinal cord, and, sometimes, your brain. This condition usually comes on quickly, over a few hours or days. You may notice some of these symptoms: Pain when you move your eyes Blurred vision Loss of color vision Trouble seeing to the side A hole in the center of your vision Blindness in rare cases Headache -- a dull ache behind your eyes Adults usually get optic neuritis in only one eye, but children may have it in both. Some people get better in a few weeks, even without treatment. For others, it can take up to a year. And a few people never fully regain their sight. Even when other symptoms clear up, they may still have trouble with night vision or seeing colors. If you have MS, heat can make optic neuritis symptoms flare up again, too -- usually after a hot shower, exercise, fever, or a bout of the flu. Once you cool off, the problems usually go away. We don't know exactly what the cause is. Doctors think it happens when something goes awry in your immune system and it attacks the myelin that covers and protects your optic nerve. The myelin gets inflamed and causes pain. Once it's damaged, it can't carry messages from your eyes to your brain. Optic neuritis has close links to multiple sclerosis. About half the people who have MS will get it. It's also an early sign of the disease. Other causes include: Bacterial infections like Lyme disease Viral infections like measles and mumps. Autoimmune diseases like sarcoidosis, lupus, and neuromyelitis optica Medications, including quinine and some antibiotics You may be more likely to get optic neuritis if you: Have MS Live at a high altitude Are white Are female Are 20-40 Have certain genes that raise your odds Even though optic neuritis symptoms go away, you will probably have: Some optic nerve damage: It may or may not cause symptoms. Vision changes: Your sight should be as sharp as it was before the optic neuritis, but you may not see colors as well. Medication side effects: The steroids most often used to treat optic neuritis put a damper on your immune system. You may get infections more easily. These drugs can also cause mood changes and weight gain. If your doctor thinks you have optic neuritis, she'll refer you to a doctor who treats eye diseases, called an ophthalmologist. You'll likely have a routine eye exam to check: Your color vision The smallest letters you can read on a chart Your side, or peripheral, vision She'll also use a test called magnetic resonance imaging ( MRI). It creates a detailed picture of your brain and helps your doctor look for damaged areas called lesions. She may inject dye into a vein in your arm. It will make your optic nerve and brain easier to see. Other tests your doctor might use include: Pupillary reaction test: The doctor will shine a bright light in front of your eyes to see how they respond. Ophthalmoscopy: It checks your optic nerve to see if it's swollen. Blood tests: They can find proteins in your blood that show you might be likely to get, or already have, neuromyelitis optica. Lumbar puncture: If both eyes are affected, if you're under 15, or if your doctor thinks you have an infection, she might use this test to check the fluid that surrounds your brain and spinal cord. You might hear her call it a spinal tap. Optical coherence tomography ( OCT): It measures the fiber layer in your retinal nerve. If you have optic neuritis, it'll be thinner than in people who don't. Visual evoked response. The doctor attaches wires to your head with small patches. The wires record your brain's responses as you watch a screen that displays an alternating checkerboard pattern. The test measures the speed at which your optic nerve sends signals to your brain. If it's damaged, they'll move more slowly. Expect to go to back to the doctor in 2 to 4 weeks to confirm the diagnosis. The condition often goes away on its own. To help you heal faster, your doctor will probably give you high-dose steroid drugs through an IV. This treatment may also lower your risk of other MS problems or delay its start if it's the cause. But while these drugs help the swelling go down, they won't make a difference in your vision. In special cases, your doctor may suggest other treatments, such as: Intravenous immune globulin ( IVIG): You may also hear it called plasma exchange. This is a medication made from blood. You get it through a vein in your arm. It's costly, and doctors aren't completely sure that it works. But it may be an option if you have severe symptoms and can't use steroids or they haven't helped you. You can get this treatment long-term if you have optic neuritis and your brain MRI shows you have lesions. Vitamin B12 shots. It's rare, but optic neuritis can happen when the body has too little of this nutrient. In these cases, doctors can prescribe extra vitamin B12. If your optic neuritis results from a disease, your doctor will treat that condition. Once your vision is back to normal, you can get optic neuritis again, especially if you have MS. If your symptoms return, be sure to tell your doctor. Report any new symptoms or those that get worse, too.