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(BrJ Ophthalmol 1996; 80: 304-308) Computer simulation of the visual field test makes it possible to investigate the interaction of patient characteristics and test strategies without the time and expense of an actual trial.The KRAKEN systeml 2 is one simulation procedure developed for use in the analysis of static full threshold perimetry. The system has been used to explore the effects of changing the variables of staircase algorithms such as the starting and final step sizes, the starting intensity, the number of reversals, and patient response variability.The staircase strategy widely used to monitor glaucoma in programs such as the 30-2 and 24-2 on the Humphrey, Henson, and Octopus perimeters,3 is a two reversal strategy with an initial step size of 4 dB changing to 2 dB after the first reversal. This strategy (4-2) is used in the current simulation with the last seen presentation being taken as the threshold estimate. The threshold estimate derived by the 4-2 strategy is subject to a certain degree of error which can be defined as the difference between the true threshold and the threshold estimated by the staircase.A patient's sensitivity and response variability at a given retinal location are well described by the frequency of seeing (FOS) curve.47This S-shaped curve gives the percentage of stimuli seen at a range of intensities which straddle the threshold. The threshold sensitivity is normally defined as the intensity at which 50% of the stimuli will be seen while response variability is represented by the

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