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

PLoS One. 2020 Jul 8;15(7):e0232784. doi: 10.1371/journal.pone.0232784. eCollection 2020.

Abstract

Purpose: Rod 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.

Methods: Monocular 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.

Results: The 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).

Conclusions: Thresholds 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.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Aging / physiology*
  • Female
  • Flicker Fusion / physiology*
  • Humans
  • Male
  • Middle Aged
  • Photic Stimulation*
  • Retinal Cone Photoreceptor Cells / cytology*
  • Retinal Rod Photoreceptor Cells / cytology*
  • Sensory Thresholds / physiology*
  • Young Adult

Grants and funding

"John L Barbur is an inventor of AVOT tests (some employed in this study); an employee of City, University of London; and a director of City Occupational Ltd. (a City University spin out company setup to manufacture and supply AVOT tests). The funder provided support in the form of salaries for author [JS], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.