Ischemia results 3 months later in altered ERG, degeneration of inner layers, and deafferented tectum: neuroprotection with brimonidine.

PURPOSE To investigate the long-term effects of transient ligature of the ophthalmic vessels (LOV) on the inner and outer retina as well as on retinotectal projection, and whether brimonidine (BMD) has protective effects. METHODS In adult rats, the left eye was subjected to 90 minutes of LOV. One hour before ischemia, 2 drops of saline alone (vehicle group) or saline containing 0.5% brimonidine (BMD group) were instilled in the left eye. The effects of LOV on the inner and outer retina were assessed with ERG recordings of a- and b-wave amplitudes at 1, 8, and 12 weeks after LOV and with analysis of layer thickness in paraffin sections. The retinotectal projection was orthogradely labeled with cholera toxin subunit B (CTB) injected in the left eye and measured in serial coronal sections of the superior colliculus. RESULTS There were significant reductions in the mean b-wave amplitudes of the ischemic eyes at 8 and 12 weeks after LOV in the vehicle-treated group of animals, but not in the BMD-treated group. The thickness of the inner nuclear and inner plexiform layers of the vehicle-treated group of retinas had decreased to approximately 71% of the thicknesses in the BMD-treated groups. Three months after LOV, the mean volume of the retinotectal projection in the vehicle- or BMD-treated group of animals had decreased to approximately 54% or 83%, respectively, of the mean values found in the control group of animals. CONCLUSIONS LOV induces degeneration of the inner retinal layers and the retinotectal projection 3 months after the insult. BMD administration significantly protected against LOV-induced retinal damage and degeneration of retinal projection.