The disc and rim areas in 15 eyes from 15 selected low-tension glaucoma (LTG) patients were compared with those in 15 eyes from 15 selected high-tension glaucoma (HTG) patients. In all patients, visual field defects (VFD) were at an early stage (mean deviation greater than -5 dB, program 30-2 of Humphrey Visual Field Analyzer, STATPAC) and were confined to either the upper or lower hemifield. There were no significant differences in the degree of VFD between LTG and HTG, and the peak intraocular pressure averaged 18.9 and 29.2 mmHg for LTG and HTG eyes, respectively. The disc and rim areas were determined from stereoscopic disc photographs using the method of Littman. The half rim area corresponding to the upper or lower hemifield without VFD was significantly smaller for LTG than HTG (LTG 0.26 +/- 0.08 mm2, HTG 0.31 +/- 0.08 mm2, mean +/- SD, n = 15, P less than 0.005). The rim area corresponding to the upper or lower hemifield with VFD was also significantly smaller for LTG than HTG (LTG 0.19 +/- 0.08 mm2, HTG 0.24 +/- 0.08 mm2, P less than 0.01). On the other hand, there was no significant difference in the disc area between LTG and HTG (LTG 1.96 +/- 0.57 mm2, HTG 2.03 +/- 0.45 mm2, P greater than 0.4). It was suggested that the differences in rim area were already present prior to the manifestation of the VFD.