The influences of stimulus wavelength and eccentricity on short-wavelength pathway isolation in automated perimetry

The aim of the study was to determine whether the suggested stimulus and background parameters employed in commercially available short-wavelength sensitive perimetry (SWAP) are clinically appropriate. Threshold versus intensity curves were measured using a modified Humphrey Field Analyser. The reduction in background luminance was achieved using aperture stops in order to avoid changes in the chromaticity of the background. Short-wavelength thresholds were determined for 440, 450 and 460 nm stimuli and were corrected for pre-receptoral absorption. Short-wavelength sensitive pathway isolation was approximately 1.5 log units and decreased with increases in eccentricity and in stimulus wavelength. It would seem that the use of a 450 nm narrowband stimulus filter would offer a compromise between both the physiological requirements and the physical properties of the stimulus. Such an approach would reduce some of the inherent between-subject normal variability associated with SWAP.