OPTIC NEURITIS – Retrobulbar

Description

Optic neuritis (ON) produces acute, and usually self-limiting, visual impairment most often in association with demyelination disease affecting the optic nerve. Inflammatory and infectious conditions may also cause ON (see next condition). Demyelination disease affecting the central nervous system, also known as Multiple Sclerosis (MS), is the most common association with retrobulbar optic neuritis in adults. In retrobulbar neuritis the optic disc appears normal during the acute episode. It is sometimes described as the condition where “the doctor sees nothing and the patient sees nothing”.

MS is a presumed-autoimmune chronic neurological disorder characterized by nerve fiber demyelination at multiple sites within the central nervous system, resulting in impaired conduction of nerve impulses. MS affects women 9 times more often than men, often begins in the third to fifth decades, and produces multiple, fluctuating neurological deficits. The Optic Neuritis Treatment Trial (ONTT) found that 38 percent of adults presenting with ON would be diagnosed with MS over the following 10 years. Optic neuritis without MS may in some instances be a local autoimmune reaction causing a similar demyelinating inflammation of the nerve.

Symptoms

The classic triad of optic neuritis consists of (1) loss of vision, (2) eye pain, and (3) impaired color vision. Vision deteriorates over hours to days, and is usually worst 1 to 2 weeks after symptom onset. ON is usually monocular. Ocular and periocular pain is highly characteristic, and is typically worse with eye movements. Patients often describe reduction in perceived light intensity and ‘washed-out’ colors. Symptoms may worsen with exercise or increase in body temperature (Uhthoff sign). Previous or current neurological symptoms (e.g., paresthesias, impaired coordination, diplopia, incontinence) may be suggestive of multiple sclerosis or other central nervous system pathology.

Signs

In retrobulbar neuritis, the disc appears quite normal. Since there are no ophthalmoscopic signs, initial diagnosis relies upon the patient’s symptoms and clinical assessment of visual performance. Acuity is variable. Color vision and contrast sensitivity are usually impaired. Visual field defects, such as a central scotoma, are common, and a relative afferent pupillary defect is usual in unilateral cases. Full neurological examination should be performed on all patients.

Prevalence

Rare (approximately 1 per 20,000 per year).

Significance

ON is the presenting feature of MS in approximately 20 percent of cases.

Differential Diagnosis

Arteritic Ischemic Optic Neuropathy, Nonarteritic Ischemic Optic Neuropathy, Papilledema, Diabetic Papillopathy, Leber Hereditary Optic Neuropathy, Toxic Optic Neuropathy.

See Also

Optic neuritis – sequential to other causes.

Management

Investigations

Magnetic resonance imaging (MRI) has become a standard investigation since the ONTT, in which the 10-year risk of developing MS was 56 percent in patients with at least 1 typical lesion on MRI, and 22 percent in those without such lesions. Other investigations may include:

• Lumbar puncture – oligoclonal bands in cerebrospinal fluid but not serum are suggestive of central nervous system demyelination.
• Visual evoked potentials – increased latency and decreased amplitude are characteristic of ON.
• Additional blood tests – to exclude differential diagnoses.

Oral and Intravenous Medications

If the decision is made to treat an acute episode of retrobulbar neuritis, then it is common to treat within 2 weeks of symptom onset. Intravenous methylprednisolone is given for 3 days, followed by 15 days of oral prednisolone. According to the ONTT, treatment may hasten visual recovery and delay conversion to MS over the following 2 years. Unfortunately, after 3 years no benefit was demonstrated.

Long-term maintenance therapy  (e.g., interferon) may delay or reduce the severity of MS. Trials have shown a decrease in the incidence and severity of demyelinating episodes in patients with MS who have lesions noted on the MRI scan.

Review

Review is conducted at 1 to 3 month intervals, and repeat MRI is often performed after 1 year. However, reduced color and contrast sensitivity are often permanent; and optic atrophy may develop, especially with recurrent attacks.