Simulations for FASTPAC and the standard 4-2 dB full-threshold strategy of the Humphrey Field Analyzer.

PURPOSE

This study evaluates the accuracy, reproducibility, and efficiency of FASTPAC, a new fast strategy for automated perimetry using 3-dB steps with single threshold crossing, compared to the standard 4-2 dB full threshold strategy by means of computer simulations.

METHOD

An "artificial patient" module was developed to create responses to stimuli by a Monte-Carlo technique from a given probability distribution. The authors performed 10,200 simulations with threshold values ranging from 0 to 50 dB.

RESULTS

Results demonstrate an 18% decrease in the number of presentations per threshold determination, which is equal to a similar reduction in testing time. For both strategies, there is a considerable influence of the starting deviation (difference between starting value and actual threshold) on threshold error (difference between estimated threshold and actual threshold): negative starting deviations lead to negative threshold errors and vice versa. This relationship is more pronounced for FASTPAC (slope 0.18 dB/dB, P < 0.0001) than for the full-threshold strategy (slope 0.13 dB/dB, P < 0.0001). In addition, fluctuations of the determined thresholds, described as the distance between the 16th and 84th percentiles of the threshold errors, increase with increasing absolute starting deviations. This is particularly true of FASTPAC:

CONCLUSIONS

The influence of the starting value on the threshold determination may lead to a considerable underestimation of visual field defects, accompanied by a higher fluctuation. This is an intrinsic property of both staircase procedures. FASTPAC, however, is more affected than the standard 4-2 dB full-threshold strategy. FASTPAC, therefore, provides time reduction at the expense of accuracy and reliability.