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 10,000 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 bulb permitted a filament life of 260 operating hours. Furthermore, the modification ensured the correct calibration of the instrument.
Hudson
C
C
Department of Vision Sciences, Aston University, Aston Triangle, Birmingham, UK.
Wild
J M
JM
Archer-Hall
J
J
D003116:Color; D004867:Equipment Design; D008027:Light; D010775:Photic Stimulation; D010783:Photometry; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D058609:Visual Field Tests / Q000295:instrumentation*