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Maximizing the dynamic range of the Humphrey Field Analyzer for blue‐on‐yellow perimetry

The conditions employed for blue‐on‐yellow perimetry (i.e. a blue stimulus filter and a high luminance yellow background) are in conflict with those that allow a maximum dynamic range. A modification is described for increasing the dynamic range of the Humphrey Field Analyzer (HFA) for blue‐on‐yellow perimetry. The position of the HFA stimulus bulb was lowered by reducing the length of both terminals. A concave mirror with a 28 mm radius of curvature was positioned behind the lowered stimulus bulb to give a filament image partly above and partly overlapping the original filament profile within the confines of the size V stimulus patch diameter. The modification achieved a 60% increase in the light output on the default 0 dB value of 10000 apostilbs and, therefore, a useable dynamic range for blue‐on‐yellow perimetry of 2.94 log units. The effective increase in voltage supply to the stimulus Kilb permitted a filament life of 260 operating hours. Furthermore, the modification ensured the correct calibration of the instrument.