Question 5: Discuss the pathophysiology of NAION, including the risk factors.

You suspect that the patient has non-arteritic anterior ischaemic optic neuropathy (NAION).

Question 5: Discuss the pathophysiology of NAION, including the risk factors.

Answer

The pathophysiology of NAION is controversial with no one mechanism definitively demonstrated. It is presumed to result from circulatory insufficiency within the optic nerve head. Blood flow through the short posterior ciliary arteries (SPCAs) is reduced in patients with NAION. One proposed mechanism is that the acute ischaemia at the optic nerve head impairs orthograde axonal transport and results in axonal oedema. This then creates a compartment syndrome in predisposed eyes (e.g. those with crowded discs).

Risk factors associated with the development of NAION include hypotension (especially nocturnal), systemic arterial hypertension, diabetes mellitus, hyperlipidaemia, anaemia,  obstructive sleep apnoea syndrome, hyperhomocysteinemia, various coagulopathies, migraine, smoking, optic disc drusen, and uncomplicated cataract extraction (Miller and Arnold 2015).

Answer ends