Long-term progression of visual field defects and related factors in medically treated normal tension glaucoma

Purpose To analyze factors related to long-term progression of visual field defects (VFD) in patients with normal tension glaucoma (NTG) under medical therapy. Patients and methods Clinical data from 622 eyes of 311 primary open-angle glaucoma and NTG patients were collected from April 2006 to March 2016. Of these patients, those with normal intraocular pressure (IOP); glaucomatous VFD judged by Anderson's criteria; corrected visual acuity ≥0.7; receiving more than 6 years medical therapy; having undergone ≥10 visual field tests performed at 6-month intervals using a Humphrey field analyzer (Swedish Interactive Threshold Algorithms standard, C 24-2 program); and having reliability coefficients of visual field testing <33% and mean deviation (MD) more than -20 decibels in the initial visual field test were included in data analysis. The relationship between MD slope deterioration at final observation and consecutive decreases in MD value during the observation period, as well as clinical characteristics and IOP-related factors, were analyzed. Results Of 134 eyes in 134 NTG patients meeting all eligibility criteria, significant MD slope deterioration was observed in 80 eyes (59.7%). MD slope deterioration was significantly associated with consecutive decreases in MD values (Cochran-Armitage trend test: P=0.0000; univariate logistic regression analysis: P<0.0001). While no significant relationship was observed between central corneal thickness, refractive error, or prevalence of disc hemorrhage, consecutive decreases in MD value was significantly related to MD slope deterioration (univariate logistic regression analysis: P<0.0001). A reduction of IOP during the follow-up period was significantly related to nondeterioration of the MD slope (multivariate logistic regression analysis: P=0.0020). Conclusion In this 6-year observation of NTG patients treated with medical therapy, the occurrence of three or more consecutive decreases in MD value was significantly associated with visual field deterioration. Reduction in IOP was postulated to be contributing in the prevention of VFD progression.