A new screening test involving the Flicker System was used to measure temporal modulation transfer function in an effort to detect early-stage glaucoma. The study involved 64 normal-tension glaucomatous eyes and 65 normal control eyes. Patients with early-stage glaucoma (stage 0-1 of the Aulhorn-Greve classification) showed a significant modulation decrease in the 20-45 Hz range, compared to the modulation in normal eyes (P < 0.05). Patients with moderate stage glaucoma (stage 2-3) also exhibited significantly decreased modulation values in the 14-55 Hz range. In the 25-45 Hz range, the reduction of modulation in patients with diffuse visual defect was more profound than in those with localized or mixed defects. The results of the present study suggest the presence of diffuse visual function deficit in glaucoma.