PURPOSE: To investigate sectoral differences in the relationship between intraocular pressure (IOP) dynamics during dark-room prone testing (DRPT) and visual field (VF) defect progression in primary open-angle glaucoma (POAG) patients. DESIGN: Retrospective, longitudinal study. PARTICIPANTS: This retrospective study included 116 eyes of 84 POAG patients who underwent DRPT and had at least 5 reliable VF tests conducted over a more than 2-year follow-up period. We excluded eyes with mean deviation worse than -20 dB or a history of intraocular surgery or laser treatment. METHODS: Average total deviation (TD) was calculated in the superior, central, and inferior sectors of the Humphrey 24-2 or 30-2 program. During DRPT, IOP was measured in the sitting position, and after 60 minutes in the prone position in a dark room, IOP was measured again. The relationship between IOP change during DRPT, IOP after DRPT, and TD slope in each quadrant was analyzed with a linear mixed-effects model, adjusting for other potential confounding factors. MAIN OUTCOME MEASURES: Total deviation slope in each quadrant, IOP change during DRPT, and IOP after DRPT. RESULTS: Intraocular pressure after DRPT and IOP change during DRPT were 18.16 ± 3.42 mmHg and 4.92 ± 3.12 mmHg, respectively. Superior TD slope was significantly associated with both IOP after DRPT (β = -0.28, P = 0.003) and IOP change during DRPT (β = -0.21, P = 0.029), while central (β = -0.05, P = 0.595; β = -0.05; P = 0.622) and inferior (β = 0.05, P = 0.611; β = 0.01, P = 0.938) TD slopes were not. CONCLUSION: Dark-room prone testing might be a useful test to predict the risk of superior VF defect progression in eyes with POAG. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.