Verification of a formula developed to predict the postoperative intraocular pressure after cataract surgery in primary angle-closure glaucoma

BackgroundThe aim of this study was to verify the accuracy of a formula predicting postoperative intraocular pressure (IOP) after phacoemulsification and intraocular lens implantation (PHCE-IOL) in primary angle-closure glaucoma (PACG). In a retrospective chart review of patients with PACG who underwent PHCE-IOL between 2011 and 2014, we collected preoperative IOP, axial length, anterior chamber depth (ACD), number of pre-PHCE glaucoma medications, and IOP and glaucoma medications at 1 month and 3 months post-PHCE.MethodsPost-PHCE IOP values at 1 month and 3 months were compared with those predicted using the formula: postoperative IOP = 6.354 + 0.186 pre-PHCE IOP × pre-PHCE ACD. Agreements between measured and predicted IOP values were analyzed using correlation coefficients and Bland-Altman plots.ResultsOf the 62 eyes included, the average pre-PHCE IOP was 19.47 ± 5.84 mm Hg. Post-PHCE IOP values were 14.94 ± 4.03 mm Hg at 1 month and 14.21 ± 3.51 mm Hg at 3 months. Patients using more preoperative medications tended to show greater postoperative declines in medication usage. Predicted IOP significantly correlated with post-PHCE IOP measured at 1 month (R = 0.314, p = 0.013) and 3 months (R = 0.325, p = 0.01). Bland-Altman plots of difference against average of measured and estimated IOP revealed two cases falling outside ± 1.96 standard deviation at 1 month, and five cases at 3 months, indicating good consistency between measurement and prediction.ConclusionThis formula was useful for predicting IOP at 1 month and 3 months after PHCE-IOL in PACG. It aids clinicians in preoperative assessment of whether PHCE-IOL alone is likely to achieve acceptable postoperative IOP control.