Sir,

The paper by Yusuf et al1 describing cases of transient artery occlusion following phacoemulsification surgery provides an important addition to the differential for visual loss following cataract extraction, and in their subsequent letter2 they suggest prospective case finding to establish what risk factors might be associated with this phenomenon. They state that OCT ‘may provide the only objective evidence of TRAO, particularly in patients not presenting in the immediate post-operative period’. Unless patients are seen acutely when the characteristic inner retinal thickening may be evident, OCT changes may be quite subtle until inner retinal atrophy develops some time later. A modality that may be helpful in this intermediate period is electroretinography, which provides objective assessment of function, with some localisation of dysfunction. The full-field flash electroretinogram (ERG) can discern inner retinal dysfunction (by selective impairment of the b-wave in comparison with a relatively preserved a-wave, giving an electronegative ERG,3 and also, more recently described, by reduction of the photopic negative response4). Electrodiagnostic testing is not as readily available as OCT, so this may not be always feasible. The development of handheld devices may allow more widespread use,5 although recordings using these devices may need greater validation. Also, more localised arteriolar insufficiency may not be detected so sensitively by full-field techniques, in which case multifocal electroretinography can be helpful. This highlights the likely added value of using objective tests of retinal function in conjunction with high-resolution imaging of retinal structure; the latter is not always abnormal when function can be markedly impaired.