Age‐related changes in flicker sensitivity with rod‐ and cone‐enhanced stimuli

Abstract

AbstractPurposeCone and rod photoreceptors are usually isolated using high light levels for cone vision and full dark‐adaptation, when only rods respond to light. Such methods are not ideal for clinical use. A new rod/cone flicker test has been designed to isolate and measure rod‐ and cone‐mediated signals in the absence of colour signals with one minute adaptation.Methods118 healthy adults (Mean age ± standard deviation: 40 ± 15 years), were investigated. None of the participants had a history of or exhibited signs of ocular disease. Rod and cone thresholds were measured monocularly in central vision and in each of the four quadrants (superonasal, superotemporal, inferonasal and inferotemporal) at an eccentricity of 5°. Temporal frequencies, stimulus sizes, background luminances and spectral composition were adjusted appropriately to achieve approximately equal thresholds with ~ 10‐fold separation in sensitivity between the rod‐ and cone‐enhanced stimuli. Flicker thresholds were measured using five adaptive (two‐down, one‐up), interleaved staircases. Spectrally calibrated, ‘neutral density’ glasses were used to enable adequate control of display luminance at low levels.ResultsThe superotemporal quadrant had the lowest mean rod and cone thresholds compared to other tested quadrants. For participants, above 50 years of age, the central rod thresholds increased 0.53% per year, whereas cone thresholds increased 0.29% per year and this decline was faster than other respective quadrants. Overall, among the locations tested, the central rod (ρ = 0.547; p < 0.005) and cone (ρ = 0.504, p < 0.005) thresholds demonstrated the strongest correlation with age.ConclusionsThe new test isolates rod and cone signals sufficiently well to detect selective loss of photoreceptor function in normal ageing. The potential use of rod‐ and cone‐enhanced tests in patients with selective loss of photoreceptors and other retinal diseases (e.g., AMD, glaucoma, diabetes) remains to be explored.