In an attempt to determine an optimal sector pattern of the central 10 degrees visual field in glaucoma, we applied the VARCLUS procedure, a new clustering algorithm provided by SAS Institute, to 379 glaucoma visual fields of the central 10-2 program of the Humphrey visual field analyzer. The subjects were 211 normal-tension glaucoma (NTG) and 168 primary open angle glaucoma (POAG) eyes with early to moderately advanced stages of visual field defects. The 68 2-degree grid test points in the central 10 degrees visual field were divided into 10 sectors. The sector pattern was compatible with the projection of nerve fiber layers and no sectors extended over the horizontal meridian. Comparison of the mean of total deviation in the sector of 76 eyes of 76 POAG patients with the maximum intraocular pressure: (IOP) > or = 25 mmHg (high-tension group) and 85 eyes of 85 NTG patients with the maximum IOP < or = 18 mmHg (low-tension group) revealed that four sectors nasal superior to the fixation were significantly more damaged in the low-tension group. We suggest that the sector pattern obtained here is useful in studying the visual field of glaucoma and that the damaging processes in the optic nervehead are not the same in the high-tension and low-tension groups.