A study was carried out to measure the thickness of the retinal nerve fiber layer (RNFL) at the optic disc border.RNFL thickness at the optic disc border was histomorphometrically measured on histological sections of 22 human eyes with normal optic nerves and 21 human eyes with absolute secondary angle-closure glaucoma. For three eyes with normal optic nerves, serial sections through the whole optic disc area were available.In the eyes with normal optic nerves, the RNFL at the optic disc border showed a double hump configuration with the highest mean thickness in the inferior quadrant (mean +/- S.D: 266+/-64 microm), followed by the superior quadrant (240+/-57 microm), the nasal quadrant (220+/-70 microm), and finally the temporal quadrant (170+/-58 microm). In the three globes with serial sections, RNFL was thickest at the inferior disc pole (397+/-58 microm), followed by the superior disc pole (313+/-38 microm), the nasal disc pole (165+/-19 microm), and finally the temporal disc pole (131+/-15 microm). In the eyes with absolute glaucoma, mean thickness of the remainder of the RNFL was 40+/-18 microm with no marked differences between the disc regions.In normal eyes, the RNFL shows a double hump configuration with its thinnest part at the temporal disc pole, followed by the nasal disc pole and the superior disc pole. RNFL is thickest at the inferior disc pole. In glaucomatous optic neuropathy, the inner limiting membrane moves backward about 60-100 microm at the temporal disc border, and more than 200 microm at the inferior and superior disc poles.