The intended aim of the false positive (FP) index is to flag perimetry test results from “trigger-happy” patients whose results cannot be trusted, i.e., examinations in which patients too frequently pressed the perimeter's response button without actually having perceived a stimulus. On that basis, researchers believe that current methods of estimating FP rates are far from optimal.

The team simultaneously evaluated FP effects in all three SITA testing algorithms (SITA Standard, SITA Fast and SITA Faster) in 126 patients (mean age 67; 51% women) with manifest or suspect glaucoma at both of their visits. The researchers then calculated inter-visit differences in mean deviation (MD), visual field index (VFI) and number of statistically significant test points as a function of FP rates and of general height.

Increasing FP values were associated with higher MD values for all three algorithms, but the effects were small, 0.3dB to 0.6dB, for an increase in FP rate of 10 percentage points rate. For VFI, this change was even smaller, 0.6% to 1.4%. The coefficient of determination, r2, the variability in the dependent variable that is explained by the explanatory variable, was very small for all strategies of FP vs. MD and even smaller for FP vs. VFI. The effects of FP were larger in severe glaucoma, with MD increases of 1.1dB to 2.0dB per 10 percentage points of FP, and r2 values ranging from 0.04 to 0.33. Numbers of significantly depressed total deviation points were affected only slightly, and pattern deviation probability maps were generally unaffected.

General height was much more strongly related to perimetric outcomes than FP was and was usually highly significant. The researchers suggested “general height or other analyses might be better suited than FP rates for identifying unreliable results in patients who frequently press the response button without actually having perceived stimuli."

Anders H, Michael PV, Flanagan JG, et al. False positive responses in Standard Automated Perimetry. Am J Ophthalmol. July 17, 2021. [Epub ahead of print].