['To compare histologically the thickness of conjunctival specimens of normal tension glaucoma (NTG) patients with primary open-angle glaucoma (POAG) patients.', 'In this prospective study, 54 patients scheduled for trabeculectomy were categorized into NTG and POAG based on their maximum untreated intraocular pressure at any time (IOPmax) as measured by Goldmann applanation tonometry. Sixteen patients with NTG (IOPmax≤21 mm Hg) and 36 patients with high tension POAG (IOPmax>21 mm Hg) were included in the study. Biopsies were taken from the superior bulbar conjunctiva during trabeculectomy. The specimens were fixed in formalin, embedded in methacrylate, histologically sectioned, stained with toluidine blue, and analyzed with a light microscope. The stromal conjunctival thickness (CT) was measured in a standardized way and compared between the 2 groups. Intergroup comparisons were performed using the Mann-Whitney U test for continuous variables and the Fisher exact test for categorical variables. The correlation between the central cornea thickness (CCT) and the CT was investigated by the Spearman test.', 'The stromal CT was significantly thinner in NTG compared with POAG (64±31 vs. 103±44 µm, respectively; P=0.002). Stromal CT of the whole group was positively correlated with IOPmax (r=0.41; P=0.002; 95% confidence interval, 0.15-0.62) but not with central cornea thickness (r=-0.005; P=0.97; 95% confidence interval, -0.28 to 0.27).'] Is the Conjunctiva in Normal Tension Glaucoma Patients Thinner Than in Primary Open-Angle Glaucoma Patients : A Comparative Histologic Study?