Figure 2. Time-dependent histological changes of rat optic nerves (ONs) induced by ocular hypertension (45 mmHg). Evaluation was performed four weeks after the injury. A: Representative images of cross-sections of ONs from rats treated with 0 (control), 1, 2, 3, 4, 5, 6, or 7 h of elevated intraocular pressure (IOP; 45 mmHg). In the control, which was subjected to 1–4 h of pressure, there was no identifiable axonal swelling or damage or gliosis in the ON. When the duration of ocular hypertension was 5 h or longer, there was apparent axonal damage (darkly stained axons) and swelling, and gliosis (lightly stained) became obvious. B: Higher magnification images of an ON from a control rat and one that had elevated IOP for 5 h, showing axonal damage. C: Semi-quantitative analysis of pressure-induced ON damage using the Optic Nerve Damage Score (ONDS). Each symbol represents mean±SEM (n=8). *p<0.001 versus the control group using a one-way ANOVA and a Dunnett’s test.