Increase of retinal layer thickness in a rat model of acute intraocular hypertension

We investigated the retinal response to acute elevation of intraocular pressure (IOP) in rat eyes. IOP elevation was induced in the right eyes of adult Wistar rats using laser photocoagulation of the trabecular meshwork, while the left eye served as untreated controls. Retinal layer thickness was measured in vivo using a home-built spectral-domain optical coherence tomography (SD-OCT) system. Glial cell reactivity was assessed using immunofluorescence staining for glial fibrillary acidic protein (GFAP). IOP was significantly increased in treated eyes one day after laser treatment (31.4 ± 6.4 mmHg), returning to normal in most animals by the second day (10.1 ± 2.0 mmHg). We followed the retinal layer thickness for 4 weeks (n = 14) with a subset for 9 weeks (n = 5). OCT images showed a significant increase in retinal layer thickness that persisted for 9 weeks. Histological analysis of retinal sections corroborated the in vivo OCT findings. Furthermore, the immuno-biochemical analysis revealed a marked GFAP upregulation, primarily in the retinal nerve fiber layer (RNFL). Quantification of retinal ganglion cells (RGCs) showed no significant loss of RGCs in the treated eyes in ten days after laser photocoagulation. These findings demonstrated that acute IOP elevation in this rat model induces a persisted significant increase in retinal layer thickness, rather than the commonly expected decrease in RNFL thickness. This thickening is associated with the activation of glial cells, suggesting a potential mechanism for this response.