Risk factors of non-arteritic anterior ischemic optic neuropathy (NAION): ocular or systemic.

We retrospectively analyzed 22 patients with non-arteritic anterior ischemic optic neuropathy (NAION) seen at Chung-Ho memorial hospital between 1994 and 1996 to investigate the risk factors of NAION. The risk factors were divided into two groups: ocular and systemic. The ocular factors include refractive state, intraocular pressure, and cup-disk ratio of fellow eye. The systemic factors include diabetes, hypertension and cardiovascular diseases. The analysis revealed:(1)only 22.6% of patients with NAION have systemic risk factors;(2)intraocular pressure is not specific to NAION;(3)most of fellow eyes(72.6%)have cup-disk ratio not more than 0.1; and (4) most patients (90.9%) are hyperopic or emmetropic, only 9% of patients are myopic in either affected or fellow eyes. The statistical comparison between ocular (including cup-disk ratio and refractive state) and systemic factors is significant. The correlation with systemic factors in our study was not so high as previous study had reported. On the contrary, crowding effect of small cup-disk ratio, which induces a vicious circle of generally circulatory compromised disk, may play an important role in NAION. Besides, hyperopic or at least emmetropic eyes are more prone to NAION than myopic eyes. This may be due to lack of flattening of the temporal excavation, therefore adding a predisposing factor to a generally circulatory compromised disk. The risk factors associated with NAION seem more strongly correlated with ocular factors than with systemic factors.