Changes in the Outer Retina After Acute Increase of the Intraocular Pressure in Adult Mice

Abstract

Purpose: : To investigate the effects of increased intraocular pressure on the outer retina and its circuitry.

Methods: : Adult male swiss mice (30-45 g) received a mean of 75 laser impacts (532 nm wavelength, 300 mW power, 0.5 second duration, 100 µm diameter spot size) over the limbar and episcleral veins of the left eye. Intraocular pressure (IOP) was measured in both eyes with the Tonolab tonometer prior to and at 12 h, and 1, 2, 8 or 20 wks after lasering. Full field electroretinographic (ERG) responses were recorded from both eyes prior to and 1, 2, 8 or 20 wks after lasering. Mice were processed at 3 (n=5), 9 (n=4) or 21 (n=4) wks after lasering. Cryostat retinal sections were immunolabeled with antibodies against different neuronal markers. Images were obtained by fluorescent confocal microscopy.

Results: : Laser treatment induced an increase in mean intraocular pressure of approximately 130% over baseline 12 hours after lasering but reached basal levels by 1 wk. Three and 9 weeks after lasering, immunostaining with recoverin and transducin antibodies could not document any changes in the outer nuclear layer (ONL), where the number of photoreceptor nuclei was preserved, but both ON-rod bipolar and horizontal cells had lost their dendritic processes in the outer plexiform layer (OPL). Sprouting of horizontal and bipolar cell processes were observed into the ONL. Twenty one weeks after lasering, mice with severe impairment of their ERG (disappearance of b-wave) presented an important loss of photoreceptor cells. Kinase-C antibodies showed morphologic changes of ON-rod bipolar cells and Calbindin staining showed abnormal horizontal cells and a diminished number of these cells. Mice with b-wave partially affected showed a smaller loss of photoreceptors and lesser changes in the OPL.

Conclusions: : Increased intraocular pressure by laser photocoagulation of the perilimbar and episcleral veins in swiss mice results in changes of cell morphology in the outer retina and impairs retinal inner and outer circuitries.

Keywords: photoreceptors • electroretinography: non-clinical • intraocular pressure