Purpose
To investigate cluster-based characteristics of visual field progression in low tension glaucoma (LTG) and high tension open-angle glaucoma (HTG) using 2 trend-based analysis methods.
Methods
Records of glaucoma patients with ≥30 months of follow-up and ≥6 standard automated perimetry (SAP) tests were reviewed. Inclusion required age ≥40 years, visual acuity ≥20/40 and reliable SAP. LTG was defined as untreated IOP ≤21mmHg, no history of IOP >21mmHg, open iridocorneal angles, reproducible glaucomatous SAP abnormality and corresponding optic nerve damage. The 2 groups were matched for age, follow-up time and baseline MD. SAP test locations were grouped into 10 clusters based on the topographic distribution of the RNFL. Progression was determined using: A) Corrected Cluster Trend Analysis (CCTA; EyeSuite, Haag-Streit, Switzerland), defined as progression rate (dB/yr) in mean pattern deviation (PD) values of each cluster at p<0.01; B) Pointwise Linear Regression Analysis (PLR; ProgressorTM, UK) defined as pointwise progression rate at p<0.01 in ≥1 location in each cluster. Random effect models, ANOVA, and regression analyses were performed.
Results
70 eyes (35 LTG, 35 HTG) were enrolled. Patients with LTG and HTG had similar age (71.5±8.9; 72.0±9.0yrs; p=0.79), follow-up time (60.9±22.4; 64.3±29.2mos; p=0.58), treated IOP (14.4±2.9; 14.6±3.9mmHg; p=0.78), baseline MD ( 4.5±4.0; -4.4±4.0dB; p=0.91), and rate of loss in MD ( 0.33±0.57; -0.15±0.72 dB/yr; p=0.27). The rate of loss in square root of loss variance (sLV) was worse in LTG (0.27±0.38dB; p=0.01) vs HTG (0.03±0.39dB). More LTG eyes were classified as progressors compared with HTG eyes using CCTA (26 vs 17; p=0.048) and PLR (27 vs 16;p=0.01). The number of progressing LTG eyes in inferior arcuate cluster was higher than the number of progressing HTG eyes (12 vs 4; p=0.03) but was similar (p>0.05) in all other clusters using CCTA. The cluster-based rates of loss were steeper in LTG in inferior arcuate ( 0.17±0.43dB/yr; p=0.03) and inferior paracentral clusters ( 0.33±0.62dB/yr; p=0.02) vs HTG ( 0.01±0.28 and -0.04±0.67dB/yr) using CCTA. Both methods agreed on 25 LTG and 16 HTG progressors, and 2 LTG and 0 HTG non-progressors (kappa=0.40;p=0.01).
Conclusions
Paracentral and arcuate clusters progress faster and more frequently in LTG compared with HTG and should be monitored more closely.
Keywords: 758 visual fields