Blue‐on‐yellow perimetry

Abstract

SummaryLaboratory based studies which employ foveal stimuli have demonstrated a selective short‐wavelength sensitive (SWS) pathway deficit prior to visual field loss in glaucomatous patients. Early glaucomatous visual field loss as revealed by conventional perimetry, however, is generally accepted to occur outside the fovea. Consequently, blue‐on‐yellow perimetry was developed which permits the assessment of SWS function across the central visual field. This new clinical technique employs a blue stimulus to preferentially stimulate the SWS pathway and a high luminance yellow background to saturate the other receptor types. Clinical studies suggest that blue‐on‐yellow perimetry reveals early glaucomatous field loss before conventional perimetry which follows a pattern dictated by the anatomy of the retinal nerve fibre bundles.Blue‐on‐yellow perimetry is particularly prone to attenuation by the ocular media and macular pigment because of the use of a short‐wavelength stimulus. Ocular media absorption (OMA) increases with increase in age (approx. a 10 dB increase in mean OMA between 20 and 70 years relative to 410 nm), exhibits a large variation between individuals of the same age (approx. 9 dB) and is exaggerated in diabetics. Both OMA and forward light scatter (LS) result in a diffuse reduction of blue‐on‐yellow sensitivity. Macular pigment absorption (MPA) does not vary systematically with age (P > 0.05) but exhibits a large variation between individuals (approx. 10 dB relative to 460 nm). MPA results in a symmetrical reduction of blue‐on‐yellow sensitivity centred on the fovea (mean foveal MPA 4 dB, P < 0.001) with 5° eccentricity.The psychophysical techniques employed to quantify OMA, forward LS and MPA are time‐consuming and not suitable as routine clinical procedures. Methods of analysis which avoid the use of absolute sensitivity values need to be employed to identify abnormality in the blue‐on‐yellow visual field. Such an approach may rely on the identification of change in shape (i.e. pattern standard deviation) or symmetry (i.e. glaucoma hemifield test) of the visual field. Alternatively, the clustering of stimulus locations with markedly reduced sensitivity and the conformity of clusters to recognized patterns of glaucomatous nerve fibre loss should provide sensitive measures of abnormality.