Objective To analyse the changes of nitric oxide and nitric oxide synthase in rat retina under acute high ocular pressure and study the effect of nitric oxide in rat retinal damage under hypertension. Methods Sixty Wistar rats were divided randomly into five groups:Ocular hypertension 30 min,60 min,90 min and 12 h,24 h after reperfusion．Elevation of the ocular pressure in the anterior chamber of the rat eye ca used retina ischemic damage．The changes of retinal nitric oxide content were ob served indirectly by measuring NO2－/NO3－ content in retina.The distribution and changes of neuronal constitutive nitric oxide synthase (ncNOS)were studied by immunocytochemical localization of ncNOS. Results ncNOS positive neurons were distributed in the inner nuclear layer (INL),ganglion cell layer (GCL) and the inner plexiform layer of the normal and ischemic rat retina.During acute high IOP 30 min,60 min and 90 min,NO content decreased gradually and ncNOS immune activity weakens.During reperfusion,NO content increased remarkably (Plt;0.05) as compared with the groups of hypertension 90 min and decreased remarkably as compared with the normal rat retina.But ncNOS positive neurons continue to decrease compared with the groups of hypertension 90 min. Conclusion NO participates the rat retinal injury by acute elevated intraocular pressure, and nitric oxide synthetized by ncNOS may play an important role in protecting the retina from ischemic and post-ischemic injury.