A 60-year-old woman noticed gradually worsening blurred vision in the right eye for several weeks. The patient had history of anxiety and depression. She had never smoked cigarettes and drank alcohol only socially. An optometrist had assessed her vision 2 weeks after the symptoms had begun and recorded visual acuity of 6/60 right and 6/6 left, with a mild right relative afferent pupillary defect, but normal ophthalmoscopic examination. One month later, her right eye vision had worsened, with a slowly progressing left eye blurry vision as well. An ophthalmologist recorded vision of counting fingers only in the right eye and 6/30 in the left eye. There was a mild right relative afferent pupillary defect on the right but again ophthalmoscopy was normal bilaterally. An MR scan of the brain and orbits without contrast was interpreted as normal.

QUESTION 1. WHAT IS THE DIFFERENTIAL DIAGNOSIS FOR THIS PATIENT'S BILATERALLY DECREASED VISION?

She has severely decreased central visual acuity in each eye with a mild right relative afferent pupillary defect but normal appearance of the optic nerve heads, suggesting a bilateral retrobulbar optic neuropathy. Table 1 lists the possible causes of this with pros and cons for each condition.

Non-glaucomatous optic neuropathy in patients aged over 50 years has several possible causes.

Non-arteritic anterior ischaemic optic neuropathy is the most common of these. However, this can be excluded since non-arteritic anterior ischaemic optic neuropathy requires the presence of a swollen optic nerve, whereas in this case, both optic nerves appeared normal at the time of her visual loss. Also, the onset of visual loss is sudden in this condition whereas here it was of gradual onset.

Arteritic ischaemic optic neuropathy (giant cell arteritis) should also be considered in anyone over the age of 50 with the new onset of optic neuropathy. It is usually anterior (ie, presents with optic nerve …