Sir,

Sudden onset of optic neuropathy in the elderly is most frequently vascular in aetiology; however, when bilateral, the diagnosis of LHON should still be considered. We report the oldest documented case of visual loss due to LHON.

Case report

A 73-year-old man presented with severe painless sequentially bilateral visual loss over the past few weeks. He recorded counting fingers vision bilaterally, but ocular examination was unremarkable with only mild dry age-related macular degeneration, normal retinal vessels, and healthy looking optic discs. Investigations including fluorescein angiography, CT scan of head and orbits, and extensive blood testing failed to provide any explanation.

He was a known hypertensive with a history of previous myocardial infarction and peripheral vascular disease requiring bilateral femoral bypass grafting. Carotid Doppler ultrasound scanning demonstrated internal carotid artery stenosis of >70% on the side of the initially affected eye, but no significant stenosis on the other side.

A family history of LHON was elicited. Genetic screening to investigate this possible diagnosis was undertaken which found a guanine to adenine mutation at position 11 778 on the mitochondrial DNA. His optic discs had become pale by the 10th week after presentation and he could see only hand movements.

Comment

LHON is a maternally inherited condition caused by point mutations in the mitochondrial DNA. Penetrance, independent of genotype, is estimated at 25–50% in males and 5–11% in females,1 visual loss becoming bilateral within 1 year in 97% of cases. The typical interval between eyes is 2–4 months, although simultaneous bilateral involvement is reported.2

Of patients who eventually suffer visual loss, almost 70% will do so before the age of 30.2 Those unaffected by the age of 50 are >95% likely to remain so, although asymptomatic carriers have been found to demonstrate significant subtle chronic changes such as peripapillary microangiopathy, retinal nerve fibre layer thickening,3 and colour vision deficit.4

Metabolic or ischaemic factors are well-recognised triggers to visual loss in LHON. The precipitant of visual loss in our patient was felt to be ischaemia due to vascular disease leading to an exceptionally late clinical presentation.

This case demonstrates that there may be no upper limit to the age at which LHON should be considered in the differential diagnosis of bilateral or sequential optic neuropathy.