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

Abstract

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.

Short wavelength automated perimetry

“…A narrowband blue stimulus, originally employed by Sample and colleagues (Sample & Weinreb 1990, 1992; Sample et al 1993), ensures greater SWS pathway isolation than a broadband filter and is less susceptible to shifts in the peak retinal wavelength due to ocular media absorption (Sample et al 1996) but reduces the dynamic range of the perimeter due to the reduced transmission of the filter (Moss et al 1995; Hudson et al 1993). A broadband stimulus employed by Johnson and colleagues (Johnson et al 1993ab, 1995a; Demirel & Johnson 2001) and by others (Moss et al 1995; Hudson et al 1993; Wild et al 1995; Wild & Moss 1996) increases the dynamic range of the perimeter but may, in the presence of an extensive SWS defect, stimulate the MWS pathway (Sample & Weinreb 1990).…”

“…Yeh and colleagues (Yeh et al 1989) argued that a background luminance of 300 cdm −2 was necessary for adequate saturation of the rod pathway. Johnson and colleagues (Johnson et al 1988a, 1993ab) used a background luminance of 200 cdm −2 and others of 330 cdm −2 (Hudson et al 1993; Moss et al 1995; Wild et al 1995; Wild & Moss 1996). However, Sample and Weinreb (1990) employed a background of 80.9 cdm −2 and maintained that any greater level of background luminance merely increased the SWS threshold rather than increased the magnitude of isolation.…”

Short-wavelength sensitive visual field loss in patients with clinically significant diabetic macular oedema

“…Short-wavelength automated perimetry employs a blue stimulus in order to preferentially stimulate the short-wavelength sensitive (SWS) pathway and a high luminance yellow background to saturate both the medium-and long-wavelength sensitive pathways and to simultaneously suppress rod activity [1]. Numerous studies have shown that short-wavelength perimetry detects glaucomatous visual field damage at an earlier stage in the disease process than conventional white-on-white perimetry [2±11].…”

Influence of laser photocoagulation for clinically significant diabetic macular oedema (DMO) on short-wavelength and conventional automated perimetry

“…Short-wavelength perimetry uses a relatively narrow band (cf. the polychromatic stimulus of conventional perimetry) blue stimulus to preferentially stimulate the short-wavelength sensitive pathway and a high luminance yellow background to saturate both the medium-wavelength and long-wavelength sensitive pathways and to simultaneously suppress rod activity [21,22]. The group mean times to complete each stimulus condition as a function of order for visits 2, 3 and 7 are shown in Table 1.…”