Background Many studies indicated that short-term and long-term intraocular pressure (IOP) fluctuations in primary open angle glaucoma patients might lead to glaucomatous progression. However, seldom study has evaluated the long-term fluctuation of IOP in primary chronic angle closure diseases. The objective of this study was to investigate the long-term IOP fluctuation of primary angle closure diseases and its associations following laser peripheral iridotomy (LPI) with or without laser peripheral iridoplasty. Methods A total of 158 patients with primary angle closure suspect (PACS, n=21), primary angle closure (PAC, n=81) and primary angle closure glaucoma (PACG, n=55) had been treated by LPI with or without laser peripheral iridoplasty and followed up for more than 12 months. IOP was measured with Goldman applanation tonometer. Multivariate linear regression with generalized estimating equation (GEE) regression models was used to evaluate the association of long-term IOP fluctuation (maximum IOP minus minimum IOP) with gender, age, baseline IOP, baseline peripheral anterior synechia (PAS), baseline vertical cup/disc ratio (VCDR), baseline mean deviation (MD), need for IOP-lowering medications. Results IOP fluctuation during follow-up in PACS, PAC and PACG groups were (4.83+/-2.90), (5.67+/-3.35), and (9.40+/-7.14) mmHg, respectively. IOP fluctuation was strongly correlated with baseline IOP (r=0.356, P <0.001), PAS (r=0.374, P <0.001). IOP fluctuation was higher in patients with higher baseline IOP (0.18 mmHg per unit increase, 95% CI: 0.05-0.31 mmHg). Conclusions Long-term IOP fluctuation in PACG group was larger than that in PACS or PAC group. Eyes with higher baseline IOP were observed to have larger long-term IOP fluctuation. Chin Med J 2011;124(19):3066-3069