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Q1: What are the diagnostic possibilities and what is the most likely diagnosis?
In case 1, the patient who presented with optic disc oedema, possibilities include disorders that cause optic disc swelling such as papillitis (demyelinative, diabetic), neuroretinitis (for example, cat scratch fever), toxoplasma infection, non-arteritic anterior ischaemic optic neuropathy (NAAION), toxic optic neuropathies, and neoplastic compression of the optic nerve. DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, deafness) syndrome is another condition which needs to be considered in any diabetic patient with optic atrophy. The diagnosis of NAAION was made after exclusion of other possible diagnoses. In case 2, though the patient did not present to the eye hospital until after the acute episode, the clinical picture and negative investigations supported the same diagnosis as the first degree relative.
Q2: What are the risk factors for non-arteritic anterior ischaemic optic neuropathy?
Risk factors for NAAION include conditions predisposing to macrovascular disease (diabetes, smoking, hyperlipidaemia, and hypertension) and abnormal anatomy of the optic disc (known as “disc at risk”), which is described in detail in the discussion below.
Q3: What are the therapeutic options available for this condition?
The only effective therapeutic measure is prophylactic aspirin therapy to prevent the involvement of the second eye. However, as macrovascular risk factors have been found to be associated with this condition, it would be reasonable to treat any if they are present.
NAAION is a frequent cause of visual loss in the adult population,1 and is characterised by an acute loss of central visual acuity and visual field loss (usually inferior altitudinal). It is associated with swelling of the optic disc and flame shaped haemorrhages, either within the substance of the optic disc, or in the peripapillary retina. The cause is thought to be acute ischaemia of the most anterior part of the optic nerve head with occlusion of the posterior ciliary circulation. Risk factors for macrovascular disease, including diabetes mellitus, hypertension, hyperlipidaemia and smoking, are associated with NAAION,2-4 but in addition, certain anatomical features of the optic nerve head appear to be underlying predisposing factors. Cross sectional studies have observed that patients with NAAION have a smaller optic disc and a reduced cup to disc ratio,5 and it has also been suggested that increased branching of central retinal vessels within the disc may also predispose to NAAION.6The cluster of all or some of these predisposing factors identifies a “disc at risk”. These abnormalities may provoke ischaemia secondary to overcrowding of axons as they pass through the lamina cribrosa.
Both patients had abnormal optic discs. The discs of case 1 (fig 1A, B, and C; see p 267) showed additional blood vessels and additional branches of main retinal blood vessels were also visible. In case 2, the optic discs (fig 2; see p 267) had no physiological cup in either eye. Extra branches and abnormal branching of the main retinal vessels could also be observed. Each of the patients had different macrovascular risk factors and also had features of “disc at risk”. The observation of abnormal anatomical features of the optic disc in two generations of the same family suggests that the “disc at risk” may be an inherited characteristic, which is the principal predisposing factor to NAAION. NAAION has been reported previously to occur in siblings7-9 and in twins,8 in whom it was associated with a reduced cup to disc ratio. The present cases further support the possibility that these anatomical abnormalities of the optic disc may be inherited. If this is so, recognition of a “disc at risk” before the onset of NAAION may allow the introduction of prophylactic treatment to try to prevent the onset of this disease. Though NAAION has been associated with an increased prevalence and mortality from cardiovascular and cerebrovascular disease,2 the only beneficial therapy is treatment with aspirin, reducing the risk of NAAION in the non-affected eye.10 There may be a case for screening family members of affected patients and treating them prophylactically with aspirin. In addition, any identifiable macrovascular risk factors should be treated.
NAAION is a cause of visual loss associated with oedema of the optic disc.
Macrovascular risk factors are associated with the development of this condition.
A diagnosis of NAAION should be considered when patients present with papilloedema and visual loss.
Increased awareness of this condition is required by doctors screening diabetic patients for eye complications of diabetes.
In diabetic patients, this condition can be confused with diabetic papillitis, which is a relatively benign condition with a good prognosis. It is important to consider this condition when patients present with unilateral disc oedema and visual loss, and particularly if they have any macrovascular risk factors. Although NAAION is familiar to ophthalmologists, an awareness of this condition needs to be increased among physicians in order to avoid unnecessary investigations and diagnostic confusion. In particular, it is important that doctors or optometrists who screen diabetic patients for eye complications are aware of its existence.
Non-arteritic anterior ischaemic optic neuropathy.