Causes, incidence, and risk factors
The cornea allows light to enter the eye. As light passes through the eye the iris changes shape by expanding and letting more light through or constricting and letting less light through to change pupil size. The lens then changes shape to allow the accurate focusing of light on the retina. Light excites photoreceptors that eventually, through a chemical process, transmit nerve signals through the optic nerve to the brain. The brain processes these nerve impulses into sight.
The cause of optic neuritis is unknown. Sudden inflammation of the optic nerve (the nerve connecting the eye and the brain) leads to swelling and destruction of its outer shell, called the myelin sheath.
Myelin is the layer that forms around nerves. Its purpose is to speed the transmission of impulses along nerve cells.
The inflammation may occasionally be the result of a viral infection, or it may be caused by autoimmune diseases such as multiple sclerosis. Risk factors are related to the possible causes.
Symptoms
Acute loss of vision in one eye
Loss of color vision
Pain on movement of the eye
Changes in the pupil's reactions to bright light
Signs and tests
A complete medical examination is usually used to rule out associated diseases. Tests may include the following:
Visual acuity tests may be performed in many different ways. It is a quick way to detect vision problems and is frequently used in schools or for mass screening. Driver license bureaus often use a small device that can test the eyes both together and individually.
Color vision testing
Visualization of the optic disc by indirect ophthalmoscopy
MRI of the brain to test for multiple sclerosis