Elevated intraocular pressure (IOP) is the most important modifiable risk factor associated with glaucoma development. Many experimental studies have demonstrated sustained intraocular pressure reduction after routine cataract extraction in eyes with or without ocular hypertension or glaucomatous disease.[6–8] So far, the mechanism remains poorly understood and the magnitude of this effect is highly variable and unpredictable. In patients with narrow angles, the IOP-lowering effect appears to also be proportional to the degree of anterior chamber angle deepening induced by cataract surgery. However, for POAG, the mechanism is not as clear. Many studies have focused on the relationship between the ocular anatomy and IOP reduction after phacoemulsification. Anterior chamber and angle parameters have been found to be predictive factors. For example, the ratio of the preoperative IOP and anterior chamber depth (ACD)—the pressure-to-depth ratio (PD ratio)—and changes in angle opening distance (AOD) have been reported to be associated with IOP reduction after phacoemulsification in non-glaucoma subjects.