INTRODUCTION: This study aimed to investigate intraocular pressure (IOP)-independent factors associated with the progression of primary open-angle glaucoma (POAG) with IOP ≤15 mm Hg. METHODS: POAG patients with maximum IOP ≤15 mm Hg at the Kyoto University Hospital between January 2011 and August 2021 were retrospectively enrolled. We evaluated effects of various factors on the rate of mean deviation (MD) changes in the visual field (VF) examinations using a linear mixed model. These factors included hypertension, diabetes mellitus (DM), hyperlipidemia (HL), cardiovascular disease, arrhythmia, disc hemorrhage, sleep apnea syndrome, orthopedic diseases, and malignant tumors. RESULTS: In total, 98 eyes from 68 patients were included. The baseline MD was -9.74 ± 7.85 dB. The mean rate of MD change and IOP during the observation period were -0.28 ± 0.04 dB/year and 11.8 ± 1.0 mm Hg, respectively. Comorbidity of DM or HL showed a significant positive association with the rate of MD change (β = 0.35, p = 0.0006 and β = 0.18, p = 0.036, respectively) in the model adjusted for age, sex, axial length, mean IOP, and standard deviation of IOP during the observation period. However, no significant association of DM or HL was found after adjusting for central corneal thickness. CONCLUSION: This study suggests that DM or HL is associated with VF deterioration in glaucoma with lower IOP, but the association may be due to differences in IOP characteristics.