Linear relation between structure and function.

The main limitation of the study by Danesh-Meyer et al. was neither discussed nor mentioned. The time axis was not taken into account. The functional change after an acute event such as anterior ischemic optic neuropathy (AION) is immediate, but there is a delay before the anatomic changes take place. In this study, most of the patients with nonarteritic anterior ischemic optic neuropathy (NAION) or arteritic anterior ischemic optic neuropathy (AAION) were tested a short period after the acute event, as described by the authors. In a similar study by Hood et al., the patients were tested at least 5 months after the AION event, with a median of 2.95 years. The reason was to allow sufficient time to minimize the effects of optic disc swelling and to allow the retinal ganglion cell (RGC) axons to degenerate. The results of the study in Hood et al. are obviously contrary to those presented by Danesh-Meyer et al. The relationship between a structure (optical coherence tomography [OCT]– determined retinal nerve fiber layer thickness) and function (standard automated perimetry [SAP]– determined sensitivity loss) is the same in patients with AION as in those with open angle glaucoma (OAG). It is not adequate to use visual field perimetry results as a criterion for comparison in the population examined by Danish Meyer et al., as visual acuity and visual fields improve up to 6 months from the onset of NAION. The only conclusion that can be made from the results of Danish-Meyer et al. is that a few months after the acute event of NAION/AAION the optic disc and RNFL look different than they do in OAG. Aharon Wegner Alexander Erben