In an attempt to detect patients in an early stage of glaucoma, a new screening test, the Flicker System, by which temporal modulation transfer function is evaluated, was performed in 64 normal-tension glaucoma patients and 65 normal eyes. The early stage of glaucoma, i.e., stage 0-1 of Aulhorn-Greve's classification, showed a significant decrease of the modulation in the range from 20 to 45 Hz in comparison with normal eyes (p value < 0.05). The moderate stage of glaucoma of stages 2-3 also revealed significantly decreased values of the modulation in the range from 14 to 55 Hz. In the range from 25 to 45 Hz, the reduction of modulation in the glaucoma with diffuse visual defect was more profound than in glaucoma with localized or mixed defects. The results seem to be compatible with the presence of diffuse visual function deficit in glaucoma.