Purpose: To determine if baseline diurnal intraocular pressure (D-IOP) can predict the progression rate of visual field (VF) loss in normal-tension glaucoma (NTG). Methods: NTG eyes (n = 73) with D-IOP (measured from 8 AM to 4 PM at 90-minute intervals), which had been followed-up for more than 10 years were enrolled in this study. Eyes were categorized into a low-teen NTG group (n = 30, D-IOP = 12.2 ± 1.5 mmHg) and a high-teen NTG group (n = 43, D-IOP = 15.7 ± 1.4 mmHg). In each group,

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... linear regression was used to find factors (including maximum D-IOP parameter and IOP reduction after treatment) associated with visual field index progression rate based on Humphrey VF tests. Results: In the low-teen NTG group, VF progression rate was significantly associated with age (p < 0.001), IOP reduction after treatment (p = 0.01), and maximum D-IOP (p = 0.02) after adjustment for multiple confounding factors. However, in the high-teen NTG group, age (p = 0.04) and IOP reduction after treatment (p = 0.02), but none of the D-IOP or follow-up IOP parameters, were significantly associated with VF progression rate. Conclusions: D-IOP measurement could be helpful in predicting long-term VF progression, especially in low-teen NTG eyes.