Definition & Overview
Optic neuritis is an eye condition in which the myelin lining of the optic nerve becomes inflamed. It can affect one or both eyes.
The optic nerve, which is actually a nerve tract, is the main nerve that communicates with the brain and transmits visual stimuli from the retina going to the brain stem and onto the occipital cortex, the area of the brain responsible for recognizing vision. The myelin sheath, on the other hand, is the protective layer covering the optic nerve; it also provides much-needed insulation to the nerve tracts. Thus, if inflammation occurs, the eye’s entire function is affected.
Cause of Condition
The exact cause of the inflammation that brings about optic neuritis is not known, but it is currently considered as an autoimmune disorder, possibly triggered by an infection.
Statistics show that this condition is predominantly more common among:
- Young adults aged 20 to 40 years
The incidence of optic neuritis is also widely considered as a possible or an early symptom of multiple sclerosis. In fact, a person who experiences optic neuritis has an approximately 50% risk of developing multiple sclerosis within the next 15 years. MRI scans of patients suffering from optic neuritis with no history of multiple sclerosis also showed that they had abnormalities, such as brain lesions or abnormal white matter, similar to those found in multiple sclerosis patients.
It is also related with neuromyelitis optica, an autoimmune disorder that causes inflammation of the optic nerve lining as well as the spinal cord. However, studies show that optic neuritis associated with this condition tends to be more severe than those that occur alongside multiple sclerosis.
When unrelated to these two diseases, however, optic neuritis can be caused by several possible reasons, such as:
- Bacterial or viral infections, and diseases linked to them (These include tuberculosis, Lyme disease, hepatitis B, HIV, herpes zoster, meningitis, encephalitis, sinusitis, and many others.)
- Cranial arteritis, or inflammation of the arterial lining within the skull
- Bee stings
- Systemic lupus
- Side effects of certain drugs, such as ethambutol (which is a drug used to treat tuberculosis)
- Toxins such as lead, quinine, arsenic, and methyl alcohol
- Radiation therapy
- Hereditary optic neuropathy
- Vitamin B12 deficiency
The main symptoms of optic neuritis include:
- Blurred vision
- Vision loss, more often in just one eye, but sometimes affecting both eyes
- Eye pain, especially when moving the eyes
- Loss of colour vision
- Distorted vision
- Loss of visual contrast or less vivid vision
- Decreased brightness perception
- Flashing lights
These symptoms may develop within hours or a few days after the condition begins, and may peak in a couple of weeks. They also tend to worsen when a person is exposed to heat or undergoes exercise. In most cases, vision loss is temporary and sight is restored once the condition is treated. In some rare cases, however, vision loss may become permanent.
These symptoms are harder to recognize or detect if the condition affects only one eye, since the healthy eye tends to compensate and makes vision changes in the affected eye hardly noticeable. They only become noticeable when the healthy eye is closed or covered.
Who to See & Types of Treatments Available
In some people, optic neuritis may disappear in a few weeks even when treatment is not sought. However, it is important to seek treatment if:
- The symptoms increase
- The symptoms get worse
- You experience unusual severe symptoms linked to neurological disorders such as limb numbness or weakness
Since there is a possibility of permanent blindness, it is best if any unusual symptoms involving the eyes are brought to the attention of a doctor. Most symptoms can be taken to a general physician or a family doctor, as some eye problems are associated with underlying medical problems. A general practitioner or your family doctor can simply refer you to an ophthalmologist if optic neuritis is confirmed or to a neurologist if neurological problems are suspected.
Diagnosis is done using various tests to check your colour vision, the way your eyes respond to light, and your ability to read letters on a chart. An ophthalmologist will also visually check the optic nerve for inflammation using an ophthalmoscope. Doctors may also prescribe an MRI scan to check for abnormalities in the brain and look for signs of other diseases.
The treatment of optic neuritis will depend on the diagnosis of individual cases. For cases with a definite cause, the treatment is dictated by the main cause. For example, if the condition is caused by a bacterial or viral infection, anti-bacterial or anti-viral medications will be used respectively. If a person develops the condition due to a deficiency in vitamin B12, supplementation of this nutrient will be prescribed. On the other hand, if there is no definite cause, patients are usually given high-dose steroid-based medications to help stimulate faster healing. This treatment is also effective in lowering the patients’ risk of developing multiple sclerosis. However, these drugs need to be taken with caution, as they can cause some side effects such as osteoporosis or increased susceptibility to infections, due to the effect of the steroids on the immune system.
If symptoms are severe, are not responding to steroid drugs, or the patient is not allowed to take steroids, doctors may prescribe IVIG, a special medication made from blood taken from the patient. This is a costly treatment and is still inconclusive, but may be used as a last resort when other treatments have failed.
If there is vision loss involved, sight may be restored eventually; in some cases, it could take anywhere between two weeks to three months for this to occur. The risk of permanent vision loss is quite small, as about 90 percent of patients recover their vision by the 6th month. If vision is not lost, there is still a possibility of a permanent change in visual acuity.
However, for those who have previously suffered from optic neuritis, there is a 14 percent possibility of recurrence in the affected eye and a 12 percent chance that the patient will develop optic neuritis in the other eye within the next 10 years. Recurrences should be reported to your doctor as soon as possible.
Guercio JR, Balcer LJ. Inflammatory optic neuropathies and neuroretinitis. In: Yanoff M, Duker JS, Augsburger JJ, eds. Ophthalmology. 3rd ed. Philadelphia, Pa: Elsevier Mosby; 2008:chap 9.6.
Eze P, Sra SK, Sra KK, et al. Immunology of neurologic and endocrine diseases that affect the eye. In: Tasman W, Jaeger EA, eds. Duane’s Ophthalmology on DVD-ROM - 2013 Edition. Philadelphia, Pa: Lippincott Williams & Wilkins; 2013:vol 2, chap 35.