Quantitative differences between the optic nerve head and peripapillary retina in low-tension and high-tension primary open-angle glaucoma

PURPOSE: To determine whether quantitative differences in optic nerve topography could be identified between patients having primary open angle glaucoma with normal intraocular pressure (low tension primary open-angle glaucoma [LT-POAG]) vs those with elevated intraocular pressure (high-tension primary open-angle glaucoma [HT-POAG]). METHODS: We attempted to match 31 eyes of 31 patients in the LT-POAG group on a case-by-case basis with comparable eyes of 31 patients with HT-POAG. We used the Heidelberg Retina Tomograph to evaluate the optic nerve head and retinal nerve fiber layer. RESULTS: Cup areas and cup:disk area ratios were significantly larger (P <.05), whereas rim areas, rim volumes, retinal nerve fiber layer heights, and retinal nerve fiber layer cross-sectional areas were consistently smaller, but not significantly so (P >.05), in the LT-POAG group. The inferior neuroretinal rim area was significantly smaller (P <.05) and the mean deviation of superior arcuate area was significantly greater than the opposite sector in patients with LT-POAG bur not in those with HT-POAG. A relationship between localized measurements of the optic nerve head and mean deviation was more apparent in the LT-POAG group than in the HT-POAG group. CONCLUSIONS: The optic cups were larger in patients with LT-POAG than in those with HT-POAG. Measurements of sectors of the optic disk correlated better with visual field changes in LT-POAG than did global measurements of the whole nerve head, indicating more vulnerability of the optic nerve to focal damage with low intraocular pressure.