Does anyone know anything about optical neuritis?

Anon,
There's a bundle of nerve fibers in your eye that transmit visual information to your brain. When those nerves get inflamed, it's optic neuritis. Temporary vision loss and pain are symptoms.

Coach Virginia is right, it's often found associated with auto-immune disorders, often multiple sclerosis. Some people have only one episode and it clears up; others have repeat episodes. It usually affects one eye, though may affect both.

Symptoms include pain that worsens with eye movement (generally for a week or two), some loss of vision (the degree varies), and some loss in perception of colors, particularly the red part of the color wheel.

There are several tests that an opthalmologist (eye doctor) will perform if she or he suspects optic neuritis. Some cases will get better on their own. Others may benefit from intravenous and/or oral steroids, because they help reduce inflammation.

Here's the Mayo Clinic page on symptoms, explanations, and treatments:

http://www.mayoclinic.com/health/optic-neuritis/DS00882

Has your friend been diagnosed with MS or with an autoimmune disorder, or is this the first set of symptoms he or she has had? (It's important to note that not all cases of optic neuritis result in MS. A study of 368 people who had one episode of it showed that after 10 years, just 38 percent developed the disease.)

Here's the National Multiple Sclerosis Society page on optic neuritis. There's a lot of good information here:

http://www.nationalmssociety.org/about-multiple-sclerosis/symptoms/visualSymptoms/optic-neuritis/index.aspx

Here's hoping your friend recovers quickly and completely.

The only thing I have heard about this condition is that it is associated to Multiple Sclerosis and it develops as a result of an autoimmune disorder which MS is one of them.