Optic neuritis describes inflammation of the optic nerve. This may be behind the globe, retrobulbar, involve the optic nerve head, papillitis, or sometimes affect the retinal nerve fibres, neuroretinitis. It may be idiopathic in those tending towards the condition, or triggered by an exogenous cause. Consider the following two cases.
Case 1
The mother of 16-year-old MR rang the practice explaining how her son had returned from holiday complaining of floaters in his left eye together with blurry vision. There was no reported pain and the teenager was keen to point out that he had not participated in any alcohol or drug misuse while on holiday. No other triggers for the event were identified, such as temperature changes from a hot bath or vigorous exercise.
Ocular examination
• No medical history; ‘fit and healthy’
• No family history of demyelination, though the mother had been diagnosed with Raynaud’s syndrome
• Visual acuity:
• R 6/6 N5
• L 6/6-2 N5.
• No colour vision defect detected in either eye
• Slight reduction reported in the brightness of light with the left eye compared to the right
• No ocular muscle abnormality and no pain or restriction on eye movement
• Left relative afferent pupillary defect
• Left vitreous showed vitreous floaters or inflammatory cells
• Fundoscopy revealed a swollen left optic disc with few haemorrhages and venous tortuosity (figure 1: Right optic disc appears normal with a visible capillary network on OCT-angiography. The left optic disc appears swollen, with haemorrhages and no cupping seen on the 3D image. OCT-angiography shows tortuous veins and poor visibility of the capillary network)
• OCT; swollen optic disc with superior and inferior disc thickness of 194 microns.
• OCT showed cells present in the vitreous body (figure 2) and swelling of his Henle nerve fibre layer
Figure 2: Enhance high definition scan at initial presentation (top) showing multiple cellular material in vitreous (blue arrows). Appearance after 5 weeks (bottom image) shows reduction in cellular material and reduced optic nerve swelling (red arrow).
The patient was referred urgently to an ophthalmologist with a diagnosis of isolated left optic neuritis. The ophthalmologist
concurred and referred MR to a neurologist for a brain scan. This was duly undertaken and no obvious cause for the neuritis was established (there were no signs of demyelination and no cerebral inflammation). Blood tests revealed no signs of lupus, or any other auto-immune condition, and it was deemed that the most likely cause was an isolated optic neuritis due to a viral infection. Further tests confirmed the Epstein-Barr virus to be the culprit, linked to a bout of shingles that MR had suffered at the age of 11.
No treatment was instigated, as it was thought that he would make a speedy recovery once his immune system kicked in. Furthermore, his mother was against him being prescribed oral steroids to treat the inflammation.
Outcome
Twelve weeks post-infection, his eye examination showed only a mild afferent pupil defect, no disc swelling of the left optic disc (figure 3), and the OCT showing fewer floaters present in the vitreous (see figure 2).
Figure 3: MRI scans (left top and bottom) show no hyper-intensity within the optic nerve of either eye. Fundus image (top middle) reveals disc swelling and haemorrhages. The image on the top right shows no swelling some 12 weeks later, though the disc is paler on its temporal aspect. The tortuosity of the veins has also disappeared. The OCT 3D images (bottom centre and left) reveal a very swollen left disc, less so on the right. The optic disc cupping is now visible and the vitreous cells that were present 12 weeks ago have now receded.
Epstein Barr virus (EBV) is a species of Herpes virus (type 4), and the most common virus to be transmitted by kissing. It causes glandular fever (or mononucleosis). Primary infection occurs at the age of three to six years, and the virus remains latent in the human host for life. 95% of adults are exposed to the virus and in children causes no symptoms. 40% of teenagers and adults suffer symptoms which are akin to flu or a cold some four to six weeks after infection. 9% experience neurological complications including cranial nerve palsies and optic neuritis. Symptoms of EBV infection include:
• Fatigue
• Fever
• Sore throat
• Rash
• Lack of appetite
• Swollen glands
• Muscle weakness
Blood tests in EBV will show high levels of heterophile antibodies if undertaken between two to four weeks after the onset of symptoms. The presence of three antibodies is considered as likely to point to EBV virus, as follows:
- Presence of antibody VCA Ig G shows virus has occurred some time recently or in the past
- Presence of antibody VCA Ig M shows virus is currently active or occurred very recently
- Presence of antibody EBNA indicates virus is contracted at least six to eight weeks or longer
Case 2
Fifty-two-year-old female patient NT rang the practice as an emergency one Saturday morning, having experienced a sharp pain in the right eye. Since then, she noticed a ‘black area on the top part of her vision’ and also reported some pain on movement of the right eye.
Ocular examination:
• Right mild relative afferent pupillary defect
• Right fundus healthy, with no signs of papilloedema or
papillitis
• Right colour vision showed red colour vision defect
• Left fundus healthy
• Visual fields analysis (figure 4) showed a right superior arcuate scotoma (mean deviation; -5.80Db) while the left visual field appeared normal with no scotoma (mean deviation; -0.63Db)
Figure 4: Superior scotoma in the right eye emanating from the blind spot. The retinal images show no obvious signs of neuritis suggest a true retrobulbar event.
The patient was referred to an ophthalmologist with a suggested diagnosis of right retrobulbar neuritis. She was seen by a neuro-ophthalmologist who confirmed acute retrobulbar neuritis (figure 5).
Figure 5: MRI T1-weighted image, revealing an intenisty enhancing segment of the optic nerve behind the retina (red arrow).
Optic neuritis typically presents as a unilateral optic nerve swelling, with an accompanying loss of visual acuity, in young adults between the ages of 20 and 55 years. The vision loss often occurs soon after the body temperature rises (Uhtoff’s phenomenon) and there may be altered motion perception. Patients sometimes complain of mild pain on eye movements. Around 30% of typical optic neuritis is associated with multiple sclerosis, and there is a 3:1 female to male preponderance. Optic neuritis is either idiopathic or related to demyelination. 65% of cases present as retrobulbar neuritis and 35% will present with papillitis.
Retrobulbar neuritis presents with unilateral loss of vision, but no obvious signs of optic nerve swelling on fundoscopy. This is due to the swelling being on the optic nerve as it exits from the back of the eye through the orbit (distal end of the optic nerve) as shown in figure 5.
Atypical optic neuritis describes a more progressive condition, presenting either in children under the age of 12 or adults over the age of 50. There is usually unrecoverable loss of vision and severe swelling and haemorrhaging of the optic disc. The causes include sarcoidosis, auto-immune anterior optic neuropathy or peri-neuritis. Atypical patients will respond to steroids, though may suffer a rebound on drug cessation.
Optic neuritis can be due to a number of causes:
• Inflammation: demyelination (multiple sclerosis - MS) or non-demyelination
• Infection: syphilis, Lyme disease, cat scratch disease, TB and sinusitis
• Compressive: tumour, Grave’s disease and optic disc drusen
• Hereditary: Leber’s optic neuropathy.
• Miscellaneous: lymphoma, leukaemia, B12 deficiency and radiation induced.
Studies have shown that patients with optic neuritis have a 25% chance of developing MS after 15 years even when the MRI appeared normal at onset. If one or more plaques are seen on the MRI at onset, the chance of developing MS increases to 72%. Figure 6 hopes to clarify the difference between neuritis presentations.
Figure 6
Kirit Patel is an optometrist in independent practice in Radlett, Hertfordshire.
