Comparison of the new perimetric GATE strategy with conventional full-threshold and SITA standard strategies

Abstract

Purpose: A new, fast-threshold strategy, German Adaptive Thresholding Estimation (GATE/GATE-i), is compared to the full-threshold (FT) staircase and the Swedish Interactive Thresholding Algorithm (SITA) Standard strategies. GATE-i is performed in the initial examination and GATE refers to the results in subsequent examinations.

Methods: Sixty subjects were recruited for participation in the study: 40 with manifest glaucoma, 10 with suspected glaucoma, and 10 with ocular hypertension. The subjects were evaluated by each threshold strategy on two separate sessions within 14 days in a randomized block design.

Results: SITA standard, GATE-i, and GATE thresholds were 1.2, 0.6, and 0.0 dB higher than FT. The SITA standard tended to have lower thresholds than those of FT, GATE-i, and GATE for the more positive thresholds, and also in the five seed locations. For FT, GATE-i, GATE, and SITA Standard, the standard deviations of thresholds between sessions were, respectively, 3.9, 4.5, 4.2, and 3.1 dB, test-retest reliabilities (Spearman's rank correlations) were 0.84, 0.76, 0.79, and 0.71, test-retest agreements as measured by the 95% reference interval of differences were -7.69 to 7.69, -8.76 to 9.00, -8.40 to 8.56, and -7.01 to 7.44 dB, and examination durations were 9.0, 5.7, 4.7, and 5.6 minutes. The test duration for SITA Standard increased with increasing glaucomatous loss.

Conclusions: The GATE algorithm achieves thresholds that are similar to those of FT and SITA Standard, with comparable accuracy, test-retest reliability, but with a shorter test duration than FT.

Figures

Figure 1

Frequency distribution of glaucomatous field loss, according to the scoring system of Aulhorn et al., which refers to the morphologic pattern of the glaucomatous visual field defects, and to the classification system according to Mills et al. Staging was performed according to the first SITA Standard visual field results.

Figure 2

Examination results with the four thresholding strategies: full threshold 4-2-1, GATE-i, GATE, and SITA Standard from a patient with manifest glaucoma and advanced visual field loss (Aulhorn stage III)

Figure 3

Differences between local DLS thresholds, obtained with (magenta) SITA Standard (SITA) and full-threshold (4-2-1), and with (black) GATE-i (GATE) and full threshold (4-2-1). Vertical lines: 5th and 95th percentiles; vertical bars: interquartile ranges; small dots: median values (graphic modified after Artes et al.16). All DLS values are given in standardized decibels (dBS), referring to the background luminance level, which is identical between all perimeters (10 cd/m2), instead of referring to the regular decibel scale, which is related to the maximum stimulus luminance level, which differs from instrument to instrument. The dBS values can be transformed into the Humphrey dB scale by adding 25.

Figure 4

Color-coded mean difference (in decibels) in DLS thresholds between the three fast-threshold strategies with the full-threshold strategy (4-2-1) at each location in the visual field: between the (A) GATE-i, (B) GATE, or (C) SITA Standard strategy and the full-threshold strategy. (A, ○) Five seed point locations of the full threshold and the GATE-i strategies; (C, ○) four seed point locations of the SITA Standard strategy.

Figure 5

(A) Average point-wise RMS errors of DLS thresholds, obtained with (red) full threshold (4-2-1), (light green) GATE-i for the initial examination, (dark green) GATE for subsequent examinations, and (blue) SITA Standard (SITA) as a function of average baseline sensitivity. Note that all strategies have high error rates below −5 dBS (20 dB on the Humphrey scale). The low rate of errors on the far left of the graph reflects a floor effect of range restriction of measurement for all instruments and strategies. The apparent low error rate for the SITA Standard on the far right may reflect the tendency of this strategy to terminate prematurely with high sensitivities, thereby artificially lowering variability. (B) Differences between test–retest values of local DLS thresholds as a function of baseline sensitivity. Vertical lines: 5th and 95th percentiles; vertical bars: interquartile ranges, respectively; small dots: median values. Graphics modified in accordance with Artes et al. For a description of DLS values, see Figure 3.

Figure 6

The effect of visual field severity on examination duration for FT, SITA Standard, GATE-i, and GATE. Flexible splines were fit to the data from each threshold strategy to illustrate the relationship between defect depth and examination duration.