This is a case control study with consecutive sampling technique. Samples were divided into 2 groups: (1) individuals with normal-tension glaucoma (case group) and (2) individuals without normal-tension glaucoma (control group). Each group consists of 30 individuals. Inclusion criteria for case groups: (1) Normal-tension glaucoma patient, (2) Age ≤ 50 years old, and (3) Provided written informed consent. Inclusion criteria for control group: (1) Subjects with age ≤ 50 years old, (2) No glaucomatous optical nerve papilla found in direct ophthalmoscope examination, (3) Intraocular pressure < 21 mmHg, (4) Provided written informed consent. Exlusion criteria includes normal-tension glaucoma or a non-glaucoma patient but with a tendency of platelet hyperaggregation such as in thrombotic stroke, myocard infarct, diabetes mellitus; or platelet hypoaggregation such as in uremia, liver diseases, myeloproliferative diseases, dengue fever; or drug use (aspirin, sulphinpyrazone, dipiridamol, thienopyridine, clopidogrel, glycoprotein blockers). Association between platelet aggregations with normal-tension glaucoma was evaluated with odds ratio, while association between platelet aggregation values with confounding factors was measured with multivariate analysis with coefficient of regression.