Non-arteritic anterior ischaemic optic neuropathy (NAION) is a widespread visually disabling disease in the middle-aged and elderly population.1 Based on clinical observations by Hayreh, Beck, Savino and others, a low cup/disc diameter ratio and a small optic disc have been described to be structural factors associated with the disease.1^–14 The physiological correlation between disc size and cup/disc ratios explains15 why both parameters have been connected with NAION. Hayreh and colleagues discussed that a nocturnal arterial hypotension may lead to a small circumscribed ischaemia in the optic nerve head.1 16 17 In normal-sized discs or large discs, this ischaemic event may go unnoticed and may not be associated …