Figure 1: The luminance of each stimulus begins 6 dB dimmer than the presumed threshold and increases stepwise in intensity by 4 dB with each pulse (B1-Bx) to a visibly bright luminance at which point the patient perceives the stimulus. The stimulus duration is 100 ms (C) followed by a 600 ms break (D). Information regarding the threshold is then taken into account to calculate the start values for other test locations, and is also used to estimate the level of fluctuation. At neighbouring test locations, the stimulus starts at around 8 dB lower intensity than the last seen stimulus (sub-threshold). If a stimulus is seen from the beginning (within 800 ms), it is later repeated starting at the minimum luminance level (40 dB).