OPTIC NEURITIS
What is optic neuritis?
As the name suggests, “optic” stands for eye and “neur-itis” means inflammation or swelling of nerve.
What is optic nerve?
Optic nerve is the nerve that carries signals that your eye receives from the light passing through it; to the brain, where it processes those signals and you are able to see.
Hence, optic neuritis refers to the inflammation of optic nerve. In this condition, the inflammation and demylenation of optic nerve occurs.
Now that optic nerve is inflamed, it fails to transfer those signals and you have difficulty is seeing.
Optic neuritis mainly causes pain while doing eye movement and may lead to vision loss eventually if not diagnosed and treated early.
What can be the variations of optic neuritis?
There are three types of optic neuritis:
- Papillitis – It refers to the involvement of optic disc in inflammatory and demylenating disorders.
- Neuroretinitis – The optic disc surrounds retina. In this condition, combine involvement of optic disc and surrounding retina is there.
- Retrobulbar neuritis – This condition has the involvement of optic nerve behind the eyeball. It is mainly associated with diseases like viral infection, cat-scratch fever, syphilis, etc.
What are the causes of optic neuritis?
In large proportion of optic neuritis cases, the underlying causes are unidentifiable or unknown in nature.
Some of the known causes include:
- Demylinating disorders: Such as
- Multiple sclerosis
- Delvics disease
- Acute disseminated encephalomyelitis
- Schilder disease
Parainfectious diseases : These include-
- Measles
- Mumps
- Chicken pox
- Whooping cough
Infectious disorders: They involve –
- Tb
- Cryptococcal meningitis
- Ethmoiditis
- Syphilis
Autoimmune disorders like
- Polyarteritis nodosa
- Sarcoidosis
- Guillain barre syndrome
How does optic neuritis occur?
Perivascular inflammation of inflammatory cells occurr due to the inflammation, that leads to the destruction of myelin sheath and removal of disintegrated myelin by phagocytic cells that eventually leads to disruption of axon function.
No axon function means no signal transmission, that leads to various symptoms of optic neuritis.
What are the clinical features seen in optic neuritis?
Let us first talk about the symptoms of optic neuritis. It can be both asymptomatic and symptomatic.
In asymptomatic optic neuritis, the patient may experience a sudden loss of vision and no other associated symptoms.
However, symptomatic optic neuritis has following features:
- Loss of vision – It can be sudden or progressive
- Pain in the eye
- Impairment of colour vision
- Decreased dark adaptation
- Visual disturbance in bright light
- Impaired depth perception (for moving objects particularly)
Signs that your doctor will take notice of:
- Decreases visual activity
- Impaired color vision
- Visual field changes
- Impaired contrast sensitivity
- The major diagnostic sign in optic neuritis detected by swinging flash light test.
What are the investigations performed to diagnose optic neuritis?
- Visual evoked potential – helpful in making early diagnosis of optic neuritis.
- MRI Scan for both brain and orbit – done with gadolinium contrast
What is the treatment of optic neuritis?
The first and foremost step to take is to treat the underlying cause of this disease.
There is no certain effective treatment for idiopathic and hereditary optic neuritis. Hence, symptomatic treatment is done in such cases.
- Corticosteroid therapy – oral prednisolone therapy and IV Methylprednisolone is given in case of visual loss in both eye and slow progressive visual loss.
- Interferon therapy –It reduces reoccurrence in patients with multiple sclerosis. However, it is expensive and has unknown long term benefits.