To the Editor. —Aiello et al, 1 in their correspondence in the September 1992 issue of theArchives, reported two cases of spontaneous improvement of progressive anterior ischemic optic neuropathy (AION). While I do not doubt their results, it must be noted that significant visual field defects remain. The poor prognosis in cases of AION, including the progressive subset of this condition, has been well documented. 2 In optic nerve sheath decompression, a tool has been developed whereby the perineural edema, and therefore pressure, can be reduced sooner than would occur naturally. 2 The theoretical model of progressive AION involves an initial insult that destroys axons, followed either by an increase in perineural or intraneural edema and pressure that destroys an additional number of axons or by causing axons to be more susceptible to ischemia, and thus the progression. In the patients described who had improvements in central visual acuity,