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Background Testosterone may be a possible modifiable risk factor for open-angle glaucoma (OAG) and intraocular pressure (IOP), but evidence has been scarce and conflicting. In this study we evaluated the association of testosterone and its genetic predisposition with incident (i) OAG, IOP, retinal nerve fiber layer (RNFL), and ganglion cell-inner plexiform layer (GCL +). Methods Participants aged 45–100 years were derived from the prospective, population-based Rotterdam Study. Ophthalmic examinations and serum testosterone measurements (including bioavailable and free testosterone) were performed from 1991 onwards. Follow-up took place every 4–5 years. A total of 187 out of 7898 participants were diagnosed with incident (i) OAG during follow-up. Genotyping was performed in 165 glaucoma cases and 6708 controls. We calculated sex-specific weighted genetic risk scores (GRS) for total and bioavailable testosterone. Associations with iOAG were analyzed using multivariable logistic regression. Associations with IOP, RNFL, and GCL + were analyzed with multivariable linear regression. Analyses were stratified on sex and adjusted for at least age, body mass index, and follow-up duration. Results In men, testosterone was not associated with iOAG. However, the GRS for higher total testosterone was associated with an increased iOAG risk (odds ratio [OR] with 95% confidence interval [95% CI]: 2.48 [1.18; 5.22], per unit). In women, higher values of bioavailable testosterone (2.05 [1.00; 4.18] per nmol/L) and free testosterone (1.79 [1.00; 3.20] per ng/dL) were significantly associated with increased risk of iOAG. Moreover, the GRS for higher bioavailable testosterone was associated with an increased iOAG risk (2.48 [1.09; 5.65], per unit). Higher bioavailable and free testosterone were adversely associated with IOP (0.58 [0.05; 1.10] per nmol/L and 0.47 [0.04; 0.90] per ng/dL). Higher total testosterone was inversely associated with peripapillary RNFL and GCL + (Beta [95% CI]: − 3.54 [− 7.02; − 0.06] per nmol/L and − 2.18 [− 4.11; − 0.25] per nmol/L, respectively). Conclusions In women, higher testosterone levels increased the risk of iOAG. Both IOP-dependent and IOP-independent mechanisms may underlie this association. Managing testosterone levels may be particularly relevant for the prevention of neurodegeneration in the eye. Future research should confirm these findings.