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 stim ulus filter and a high luminance yellow background) are in conflict wi th those that allow a maximum dynamic range. A modification is describ ed for increasing the dynamic range of the Humphrey Field Analyzer (HF A) for blue-on-yellow perimetry. The position of the HFA stimulus bulb was lowered by reducing the length of both terminals. A concave mirro r with a 28 mm radius of curvature was positioned behind the lowered s timulus bulb to give a filament image partly above and partly overlapp ing the original filament profile within the confines of the size V st imulus patch diameter. The modification achieved a 60% increase in the light output on the default 0 dB value of 10000 apostilbs and, theref ore, a useable dynamic range for blue-on-yellow perimetry of 2.94 log units. The effective increase in voltage supply to the stimulus bulb p ermitted a filament life of 260 operating hours. Furthermore, the modi fication ensured the correct calibration of the instrument.