Age-related change in flicker thresholds with rod- and cone-enhanced stimuli.

Amithavikram R Hathibelagal,Ahalya Subramanian,John L Barbur,Shrikant R Bharadwaj,James R E Sadler,Anil R Yadav,Hemant Khanna

doi:10.1371/journal.pone.0232784

Amithavikram R Hathibelagal, Ahalya Subramanian + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0232784

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Abstract

PurposeRod and cone photoreceptor-specific tests can be time-consuming. A new non-invasive test is described. The test is based on the measurement of flicker modulation thresholds with rod- and cone-enhanced visual stimuli, which requires only minimum adaptation time. Here, we investigated how the rod-and cone-mediated flicker thresholds vary with age.MethodsMonocular thresholds with rod and cone–enhanced stimuli were measured in 140 healthy adults, (age range: 18–75 years), foveally (0°) and at four parafoveal locations, at an eccentricity of 5° in each of the four quadrants using five, adaptive, interleaved staircases. Temporal frequencies, stimulus sizes, background luminance and spectral composition, were adjusted appropriately to achieve approximately 1 log unit separation in sensitivity between the rod- and cone-enhanced stimuli. Spectrally calibrated, ‘neutral density’ filters were used to enable adequate control of display luminance for rod enhanced stimuli.ResultsThe magnitude of central and parafoveal rod thresholds was significantly higher than the central and parafoveal cone thresholds, respectively (p < 0.001) in both the age groups. However, the rate of increase in central rod thresholds (y = 0.45x—12.79; linear regression equation) was not significantly steeper than the rate of increase in central (y = 0.29x—8.53) cone thresholds (p = 0.15). Centrally, cone thresholds showed a better correlation with rod central thresholds for the age > 45 years (Spearman correlation, ρ = 0.74, p < 0.001) compared to age ≤ 45 years (ρ = 0.41, p < 0.001).ConclusionsThresholds with rod- and cone-enhanced stimuli are largely invariant below 45 years of age and increase rapidly above this age. This age-wise normative database can be used as an effective functional-marker to assess photoreceptor sensitivities in retinal diseases.

Highlights

Flicker Modulation Thresholds (FMT) can provide a sensitive measure of changes in the temporal responses of the visual system [1]
Thresholds with rod- and cone-enhanced stimuli are largely invariant below 45 years of age and increase rapidly above this age
It has been shown that the differences in cone FMT between age-matched healthy individuals and patients with Age related Macular Degeneration (AMD) are largest in the central 5 ̊ of fixation [17], which is within the region of maximum vulnerability to damage in these patients [20, 21]

Summary

Introduction

Flicker Modulation Thresholds (FMT) can provide a sensitive measure of changes in the temporal responses of the visual system [1]. Flicker modulation thresholds measured at a single temporal frequency such as at 14 Hz is considered to be a sensitive indicator of cone function in patients with AMD, with regards to ease of testing and repeatability [7, 19]. It is desirable to develop an efficient test to measure rod- and cone-specific sensitivities within the central vision and to account for the effects of normal, healthy ageing. Such data are needed to detect loss of sensitivity that falls outside the normal limits as one might expect in patients at risk of developing and quantify the earliest losses in patients with AMD or diabetes

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