What Reduction in Standard Automated Perimetry Variability Would Improve the Detection of Visual Field Progression?

Abstract

PURPOSE. The test-retest variability of standard automated perimetry (SAP) severely limits its ability to detect sensitivity decline. Numerous improvements in procedures have been proposed, but assessment of their benefits requires quantification of how much variability reduction results in meaningful benefit. This article determines how much reduction in SAP procedure variability is necessary to permit earlier detection of visual field deterioration. METHOD. Computer simulation and statistical analysis were used. Gaussian distributions were fit to the probability of observing any sensitivity measurement obtained with SAP and the Full Threshold algorithm to model current variability. The standard deviation of these Gaussians was systematically reduced to model a reduction of SAP variability. Progression detection ability was assessed by using pointwise linear regression on decreases of -1 and -2 dB/year from 20 and 30 dB, with a custom criteria that fixed detection specificity at 95%. Test visits occurring twice and thrice per annum are modeled, and analysis was performed on single locations and whole fields. RESULTS. A 30% to 60% reduction in SAP variability was required to detect pointwise deterioration 1 year earlier than current methods, depending on progression rate and visit frequency. A reduction of 20% in variability generally allowed progression to be detected one visit earlier. CONCLUSIONS. On average, the variability of SAP procedures must be reduced by approximately 20% for a clinically appreciable improvement in detection of visual field change. Analysis similar to that demonstrated can measure the improvement required of new procedures, assisting in cost-benefit assessment for the adoption of new techniques, before lengthy and expensive clinical trials.

Choice of Stimulus Range and Size Can Reduce Test-Retest Variability in Glaucomatous Visual Field Defects

“…44 At the same time, when perimetry with size III returns a defect of À5 dB at a visual field location on one visit, it may return a defect of À20 dB or 0 dB on the next visit. 3 The ability to reduce test-retest variability in defects has the potential 8 to make perimetry a more useful clinical tool in patients with severe damage, where imaging measures are no longer useful.…”

“…Increased variability also adds time and complexity to clinical trials that attempt to assess effects of treatment. [8][9][10] Increased test-retest variability is not present for frequency-doubling perimetry, which uses large, sinusoidal stimuli. [11][12][13][14][15] Knowledge about why frequency-doubling stimuli have this property could help identify a wider range of potential new stimuli for perimetry with improved test-retest variability near and within glaucomatous defects.…”

Effect of Restricting Perimetry Testing Algorithms to Reliable Sensitivities on Test-Retest Variability

“…It remains to be seen whether this would reach the 20% reduction in variability that has been reported to be needed to reduce the average time taken to detect progression by one visit. 3 However, our study demonstrates the principle that reducing the technical range of perimetry would reduce variability not just in highly damaged regions of the visual field, but also in less damaged areas by allowing more precise thresholding within the same test duration.…”

“…However, results from perimetry are highly variable, especially in regions of more severe damage. 1,2 Simulation studies suggest that reducing variability (defined as the spread of the frequency-of-seeing [FOS] curve) by 20% would enable progression to be detected, on average, one visit sooner, 3 and more than that for many patients.…”

Towards Patient-Tailored Perimetry: Automated Perimetry Can Be Improved by Seeding Procedures With Patient-Specific Structural Information

“…Previous simulations have shown that this likely requires a reduction in variability of 20% to 40% at damaged locations. 24 Experiment Two demonstrated this magnitude of reduction only for observers making high rates of response errors. Smaller reductions in test-retest variability may still be beneficial, though, particularly in clinical trial situations where different approaches may be taken to progression detection, such as the ''wait and see'' approach recently suggested by Crabb and Garway-Heath.…”