The effect of background intensity on the components of fluctuation as determined by threshold-related automated perimetry.

We studied the effect of various background intensities on the components of fluctuation by testing 20 healthy subjects on the Humphrey Field Analyzer. Our results show little difference in the total fluctuation between two low photopic background intensities similar to those commonly used on commercial perimeters: 3.02 dB for 31.5 apostilbs (asb) and 2.77 dB for 3.15 asb. However, an increase in total fluctuation (3.74 dB for 0.315 asb and 4.24 dB for 0.0315 asb) as well as in its short-term, long-term heterogeneous, and interindividual components was seen at mesopic background intensities as compared with the low photopic range. This study suggests that in healthy individuals, little difference exists in the fluctuation resulting from differences in background intensities commonly used on commercial perimeters, whereas mesopic illumination may increase the variability of threshold responses.