Normal, age‐related differences in cone‐ and rod‐enhanced rapid flicker thresholds

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Aims/Purpose: To establish the differences in normal, age‐related, monocular thresholds and the inter subject variability in cone and rod‐mediated flicker thresholds at the point of fixation and in each quadrant at 5o eccentricity.Methods: We examined 108 normal participants aged 10 to 86 years. None had any history or signs of ocular disease. Monocular flicker thresholds were measured under stimulus conditions that favoured either rods or cones to establish the limits of flicker sensitivity and changes in inter subject variability with increasing age. Mean luminance, spectral composition, stimulus size and temporal flicker frequency were selected appropriately so as to isolate either rods or cones. The measurements were carried out at the fovea (0o) and at an eccentricity of 5o in each quadrant.Results: Below 45 years of age both cone and rod mediated flicker thresholds remain relatively stable, both centrally and in the periphery. Above 45 years, cone and rod thresholds increase exponentially with increasing age. The rate of increase in threshold with increasing age is ~ 1.4 times greater for rods than for cones. Peripheral thresholds exhibit much reduced inter subject variability for both rods and cones. Rod thresholds increased more rapidly in central vision above 45 years of age and exhibited progressively larger inter subject variability.Conclusions: Although both rod and cone‐mediated thresholds increase systematically with increasing age, two major differences have emerged. The inter subject variability remains relatively constant in the periphery for both rods and cones. In central vision, the measured thresholds reveal much greater variability which increases monotonically with age. Differences in retinal illuminance caused by variations in macular pigment optical density in central vision and selective, lens absorption of short wavelength light with increasing age account well for the large variability in rod‐mediated thresholds in central vision.