AIM: To observe the differences of damage patterns of retinal nerve fiber layer (RNFL) between acute and chronic intraocular pressure (IOP) elevation in primary angle closure glaucoma (PACG) using optical coherence tomography (OCT). METHODS: Twenty-four patients (48 eyes) with unilateral acute PACG (APACG) attack in the 6 months after admission and 36 patients (64 eyes) with chronic PACG (CPACG) were included in this prospective study. For all cases, IOP has been controlled under 21mmHg after treatment. Using stratus OCT, the RNFL thickness was assessed in eyes with PACG within 3 days, 2 weeks, 1, 3 and 6 months after IOP was controlled. Repeated measures ANOVA was used to examine the changes of RNFL thickness at different time after IOP being controlled in both acute attack eyes and unaffected fellow eyes of APACG and eyes with CPACG. RESULTS: The mean RNFL thickness for the APACG- attacked eyes increased significantly within 3 days (121.49±23.84)μm after acute onset and then became thinner along with time [(107.22±24.72)μm at 2 weeks,(93.58±18.37)μm at 1 month, (84.10±19.89)μm at 3 months and (78.98±19.17)μm at 6 months]. In APACG-attacked eyes, there were significant differences of average RNFL thickness at 5 different times after IOP was controlled (P＜0.001). In the APACG unaffected fellow eyes and CPACG eyes, there were no significant differences in mean RNFL thickness at 5 different times(F=0.450, P=0.104 in APACG unaffected fellow eyes and F=1.558, P=0.200 in CPACG eyes). There was significant difference for interaction between time periods and groups (F=1.912, P=0.003). CONCLUSION: RNFL damage patterns are different under different IOP elevated courses. In APACG, RNFL was found to be swollen and thickening right after acute attack and then becomes thinning and atrophy along with the time, while RNFL was found to be diffused thinness in CPACG.