OBJECTIVE To evaluate the contribution of various factors on the progression of visual field damage in normal-tension glaucoma. METHODS Follow-up data of 56 eyes of 56 patients with normal-tension glaucoma, all of whom had an early stage of the disease with a mean deviation of -5 decibels or greater and were followed without therapy, were analyzed using regression analysis of survival data based on the Cox proportional hazards model. Factors studied were age, sex, presence or absence of diabetes or family history of glaucoma, refraction, systolic and diastolic pressures, cup:disc ratio, ratio of area of parapapillary atrophy to disc area, the mean deviations of the studied and contralateral eyes, and intraocular pressure and occurrence of disc bleeding during follow-up, both of which were treated as time-dependent variables. The progression of visual field damage was based on the glaucoma change probability analysis. RESULTS Cup:disc ratio, ratio of area of parapapillary atrophy to disc area, and intraocular pressure were found to have significant influence on the progression of visual field damage in normal-tension glaucoma. CONCLUSIONS Intraocular pressure may be involved in the development of normal-tension glaucoma. However, further prospective studies are needed to determine the validity of such a conclusion.