Optic cup enlargement followed by reduced optic nerve head circulation after optic nerve stimulation

PURPOSE. To investigate changes in optic nerve head (ONH) circulation, visu al evoked potentials (VEPs), and ONH cupping after stimulation of the optic nerve. METHODS. Electrodes were fixed above the optic chiasma in rabbits under gen eral anesthesia. Screw-type electrodes for VEP recording were fixed on the dura. ONH circulation, intraocular pressure (IOP), and blood pressure (BP) were measured after the passage of a current of 0.1 mA, for 0.1 second (wea k stimulation), 1 mA for 1 second (moderate), 5 mA for 10 seconds (strong), or 25 mA for 10 seconds (severe). Normalized blur (NB), indicative of tiss ue blood flow and velocity, was measured in the ONH after each stimulation, by using a laser speckle circulation analyzer. Changes in VEP and ocular f undus were also recorded. The ratio of cup area (CA) to disc area (DA) was measured before and 4 weeks after stimulation. After all experiments, the O NH was histologically examined. RESULTS. Weak stimulation increased NB in ONH for 10 minutes, whereas stron g or severe stimulation significantly decreased NB for a longer time, in a dose-dependent manner. BP showed no significant change, except with severe stimulation. IOP was not significantly changed. VEP amplitude was reduced 3 0 minutes after strong stimulation. The CA-to-DA ratio was significantly in creased 4 weeks after strong stimulation. In some rabbits. disc hemorrhage occurred, followed by enlargement of disc cupping, with slight gliosis. CONCLUSIONS. Electrical stimulation of the optic nerve changed ONH circulat ion and VEPs and increased disc cupping. This technique warrants further in vestigation as an experimental model for normal-tension glaucoma.