Natural history of normal-tension glaucoma

Objective: A recently reported randomized study described the role of intra ocular pressure (IOP) in normal-tension glaucoma (NTG) pathogenesis and the effect of therapeutic lowering of IOP. This is a report of an analysis of the natural course of NTG during the time eyes were not receiving therapy, either in the time interval awaiting randomization or after being randomly assigned not to receive treatment to lower the IOP. Design: Analysis of prospectively collected data on the long-term course of a cohort of untreated subjects with normal-tension glaucoma, a subset of s ubjects enrolled in a randomized controlled clinical trial. Randomization and Subject Selection: If the field defect in the study eye t hreatened the point of fixation, the subject was randomly assigned to start on treatment immediately or to be observed without treatment until progres sion was documented. Otherwise, an eye was randomly assigned only when and if, subsequent to enrollment, it showed visual field progression, progressi on of optic disc cupping, or a new disc hemorrhage. Participants: Data were collected for this report on 160 subjects observed without treatment among a total enrollment of 260, They consist of 49 subje cts who were randomly assigned on enrollment not to receive therapy, 24 fol lowed without treatment for a time until later being randomly assigned to t reatment, 31 similarly followed without treatment and who were later random ly assigned to be followed for an additional time without treatment, and 56 who enrolled but were never randomly assigned. Main Outcome Measures: Visual field data were used in this report only from the interval during which the eye had not been assigned to receive therapy and were analyzed by two measures of progression: the "survival" time to m eeting a criterion of confirmed localized progression and the rate of chang e in the mean deviation (MD) index over time. Results: The four subgroups just described were similar at baseline, except that the average MD index was slightly better for the 56 eyes that never p rogressed during the period of follow-up. By Kaplan-Meier analysis of all u ntreated subjects combined, approximately one third showed localized progre ssion within 3 years and about half within 5 to 7 years. Of subjects follow ed for 3 years or more, 62 of 109 did not show a statistically significant negative slope of MD regressed over time, whereas the others showed a stati stically significant MD decline, mainly between -0.2 and -2 db per year. Conclusions: Some cases of NTG progress more rapidly than others. Although approximately half of cases showed a confirmed localized visual field deter ioration by 7 years, the change is typically small and slow, often insuffic ient to measurably affect the MD index. Ophthalmology 2001;108:247-253 (C) 2001 by the American Academy of Ophthalmology.