Background: The main objective of this analysis was to assess the impact of severity of disease on the quality of life (QoL) of patients with ocular hypertension (OHT) and early, moderate, or advanced primary open-angle glaucoma (POAG). Methods: This multicenter study was conducted at 2 university hospitals and 13 ophthalmology practices in Germany. QoL data were assessed by the Health Utility Index (HUI3) and the 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25). Results: 154 patients (17.5% OHT, 27.9% early, 22.7% moderate, and 31.8% advanced POAG) were included. The HUI3 scores for OHT, early, moderate, and advanced POAG were 0.87 ± 0.09, 0.85 ± 0.15, 0.75 ± 0.23, and 0.58 ± 0.32, respectively. Compared to a normal population matched by age and gender, for moderate and severe POAG a difference of -0.06 ± 0.24 and -0.19 ± 0.28, respectively, was observed. NEI-VFQ-25 scores illustrate different dimensions of the impact on QoL; reduced peripheral vision or difficulties to drive a car were more crucial to glaucoma patients than social factors. Conclusions: The key difference for QoL impairment in glaucoma lies between OHT/early POAG versus moderate/severe POAG, hence every possible effort needs to be made to prevent disease progression over this threshold.