Multifocal pupillographic perimetry with white and colored stimuli

We investigated issues that could impair the capacity of multifocal pupilliographic perimetry to detect visual field damage. Differential blue light absorbance causes between-subject variance so we compared stimuli with differing blue content. We also quantified declining response gain at higher stimulus intensities (saturation), which can reduce sensitivity to changes in the visual field.

Independent stimuli were delivered to 44 regions of both eyes whereas pupil responses were recorded under infrared illumination. Luminance-response functions were measured at 88 locations for white, yellow, and red stimuli at luminances ranging from 36 to 288 cd/m2. Response saturation was quantified by fitting power functions: Response =α Luminance, z<1 indicating declining response gain. Experiments were conducted on 2 groups containing 16 and 18 different normal subjects. The second experiment was designed to confirm the results of the first and to include red stimuli.

Response saturation occurred in all visual field regions: the mean exponents ranged from 0.57 ± 0.01 to 0.74 ± 0.02 (mean ± SE), that is up to 30 SE away from an exponent of 1 (no saturation). The stimulus-response functions appeared to be determined by luminance rather than color. Signal to noise ratios and regional visual field sensitivities were similar for all stimulus colors.

Response saturation was a feature of all visual field locations. Stimuli with reduced blue light content produced the same signal to noise ratios as white stimuli. Given that these stimuli would not be affected by variable lens brunescence, they might be preferable for perimetry.