Some patients may become stressed when they are informed they have developed glaucoma. Clinicians should be aware that informing patients of the diagnosis of glaucoma might be associated with a reduction in the patient's mental health. To test whether mental health status as assessed by the National Eye Institute's Visual Function Questionnaire-25 (VFQ) decreases in patients with ocular hypertension after the diagnosis of early primary open-angle glaucoma (POAG). This cohort study was a post hoc analysis of prospective data from The Ocular Hypertension Treatment Study (OHTS) phase 1 and 2 among all participants with ocular hypertension who developed early POAG and had completed a VFQ within 2 years before and within 2 years after POAG diagnosis. The VFQ was administered every 2 years between January 2001 and December 2008. Propensity-matched participants with ocular hypertension who did not develop POAG over the same period were selected as controls. This analysis was conducted between March 7, 2024, and March 20, 2025. The main outcome was change in VFQ mental health score before and after POAG diagnosis in the POAG group compared with change over the same period in matched controls who did not develop POAG. Fifty participants developed POAG and met criteria for inclusion (mean [SD] age, 67.9 [9.2] years; 21 [42%] female; and 17 [34%] Black). There were 100 matched OHTS control participants who did not develop POAG (mean [SD] age, 66.6 [9.3] years; 37 [37%] female; and 34 [34%] Black). Among participants who developed POAG, the mean (SD) pre-POAG and post-POAG VFQ mental health scores were 94.5 (8.6) and 88.0 (13.6), respectively, for a mean (SD) change of -6.5 (11.3). In the matched control group, the mean (SD) preperiod and postperiod VFQ mental health scores were 93.3 (8.9) and 92.6 (8.0), respectively, for a mean (SD) change of -0.7 (8.3). The mean (SD) difference between the POAG group and control group in pre- and post-VFQ mental health scores was -5.8 (9.4) (95% CI, -9.05 to -2.60; P = .048). These findings support the need for further studies to confirm the association between POAG diagnosis and a decrease in mental health score and to develop strategies to inform patients about their POAG diagnosis without producing undue distress, anxiety, and depression.