Acute loss of vision in optic neuropathy

CASE STUDY - Dr Louise Warburton was surprised to learn that a teenage boy could go blind overnight

Andrew first contacted the surgery because of deteriorating vision.

He was 15 years old and was struggling to see the blackboard at school.

His mother had taken him to an optician, who was alarmed to find that his visual acuities were 2/60 and 6/60 and arranged immediate assessment at the local eye A&E.

The visual impairment was confirmed, but only a routine outpatient appointment for six weeks' time was organised.

Understandably, Andrew's mother was worried and wanted to arrange a private consultation with an ophthalmologist, hence her visit to the surgery to get a referral letter.

The consultant who saw Andrew was concerned that his vision had been deteriorating for two to three weeks.

LOSS OF VISION

Visual assessment and several other methods of testing confirmed the poor visual acuities. Andrew's near vision was 2/12, which also confirmed a genuine loss of vision.

There had been some suggestion at the original eye A&E appointment that his visual loss might be hysterical.

A tentative diagnosis of acute optic neuritis was made and Andrew was treated with high-dose pulsed steroids, but this did not make any difference to his symptoms. An MRI of the brain was normal.

Andrew was then referred to a regional eye specialist, who diagnosed Leber's hereditary optic neuropathy or atrophy. A blood test was positive for the condition.

Enquiry revealed that a relative on the maternal side had suffered from optic atrophy at the age of three, though no diagnosis was ever reached.

Leber's hereditary optic neuropathy is a maternally linked mitochondrial genetic disease that preferentially causes blindness in young, adult males, affecting one in 25,000 of the British population. It is characterised by bilateral subacute loss of central vision owing to focal degeneration of the retinal ganglion cell layer of the optic nerve. Peripheral vision remains. It is the most common cause of optic atrophy.

SUDDEN ONSET

It is likely that environmental factors like smoking or exposure to carbon monoxide contribute to the onset of visual failure. There is sometimes spontaneous recovery, but this is rare.

I personally was not aware that a young boy could go virtually blind overnight like this. It is certainly devastating to him and his family.

There are many causes of sudden loss of vision, such as massive vitreous haemorrhage or retinal causes like retinal artery occlusion. Others include ischaemic optic neuropathy, stroke causing homonymous hemianopia, migraine or acute glaucoma. Quinine or methyl alcohol poisoning can also cause sudden loss of vision.

Some of these will cause unilateral loss of vision. Andrew had bilateral deterioration. With a normal fundoscopic examination and normal pupillary reactions, the most likely cause for his problem was an optic neuritis.

OPTIC NEURITIS

Optic neuritis occurs in the 20-45 year age group and is associated with multiple sclerosis. Patients complain of impaired vision and impaired colour discrimination.

In Andrew's case, his symptoms were most suggestive of an optic neuritis and he was correctly referred for urgent assessment. It is worth remembering that all causes of visual loss, including suspected hysterical cases, need to be referred for assessment.

Optic atrophy can be caused by a sudden blow to the head, causing ischaemia of the optic nerve. A history of head injury would, however, be apparent.

Ischaemia of the optic nerve can also occur because of giant cell arteritis.

This is the most important ophthalmic condition seen in general practice and usually occurs over the age of 60. The history is of malaise, weight loss, headache and sudden, profound visual loss. The ESR is characteristically raised.

This is a medical emergency and should be referred for urgent assessment.

Treatment is with high-dose steroids.

Leber's hereditary optic neuropathy is an uncommon presentation in general practice, but GPs need to be aware of the complications and refer promptly, and to take all complaints of poor visual acuity seriously.

- Dr Warburton is a GP in Ironbridge, Shropshire

LESSONS LEARNT FROM THIS CASE

- An unusual history should always be investigated properly.

- It is important to determine the correct cause of sudden loss of vision, especially in a young patient.

- GPs should be aware of uncommon presentations and their possible complications.

- All cases of visual loss should be referred for assessment.

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