June 2022
Volume 63, Issue 7
Open Access
ARVO Annual Meeting Abstract  |   June 2022
Background Adaptation, Stimulus Duration, and the ON and OFF Components of the Full-Field Photopic Flash Rat Electroretinogram
Author Affiliations & Notes
  • James D Akula
    Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
    Ophthalmology, Harvard Medical School, Boston, Massachusetts, United States
  • Emma Ziska
    Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
    Northeastern University, Boston, Massachusetts, United States
  • Jashwa Peralta
    Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
    Northeastern University, Boston, Massachusetts, United States
  • Rithvik Manne
    Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
    Northeastern University, Boston, Massachusetts, United States
  • Jagvi K Patel
    Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
  • Footnotes
    Commercial Relationships   James Akula None; Emma Ziska None; Jashwa Peralta None; Rithvik Manne None; Jagvi Patel None
  • Footnotes
    Support  NIH EY028953
Investigative Ophthalmology & Visual Science June 2022, Vol.63, 757 – F0409. doi:
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      James D Akula, Emma Ziska, Jashwa Peralta, Rithvik Manne, Jagvi K Patel; Background Adaptation, Stimulus Duration, and the ON and OFF Components of the Full-Field Photopic Flash Rat Electroretinogram. Invest. Ophthalmol. Vis. Sci. 2022;63(7):757 – F0409.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : To assess the impact of light adaptation on the ON and OFF contributions to the amplitude of the photopic b-wave in the rat.

Methods : Electroretinograms (ERGs) were elicited from Long-Evans rats using 4–512 ms (5 durations) stimuli in the presence of 6–500 cd/m2 (5 intensities) backgrounds. Stimuli were 3–518,240 cd/m2. In respective sessions covering each of the 25 combinations of duration and background, nine flashes of increasing Weber contrast (0.5–1,036) were presented. To determine if an "equivalent background" could be measured, photopic b-waves were elicited in the dark, 800 ms after a 262 cd.s/m2 conditioning flash (CF). The respective depolarizing (ON) and hyperpolarizing (OFF) components of each ERG were estimated by optimizing a sum of sigmoidal curves to the stimulus/response (SR) data at multiple timepoints along the ERG traces (Akula et al., 2019). Finally, b-wave amplitude SR data were fit with the Naka-Rushton (NR) equation to estimate the semisaturating intensity (σ).

Results : The b-wave SR function never displayed the "photopic hill" characteristic of the human response. Although it varied by session, across stimulus duration and background intensity, the respective mean maximal derived ON and OFF response was >200 and <40 µV. At fixed stimulus duration, the Weber contrast at σ was stable across background intensity. The "equivalent background" of the CF, assessed from σ, was ~290 cd/m2.

Conclusions : First, in contrast to the human photopic ERG OFF response, which is of approximately equal amplitude to the ON, in rat the OFF response is <1/5th as large as the ON. This may have important implications for rat daytime vision and likely explains the lack of a rat "photopic hill" (notably, all human conditions characterized by a lack of photopic hill are believed to cause ON pathway deficits). Second, regardless of stimulus duration, amplitudes of the photopic b-wave and its constituent ON and OFF components are mediated by stimulus contrast rather than intensity. Therefore, accurate absolute calibration of photopic stimuli is of secondary importance to internal (i.e., relative) consistency, mitigating issues such as pupil size and instrumentation differences. Third, the value of the NR σ parameter can be used to determine equivalent background, such as for conditioning flashes, which may be of use in designing certain experiments into cone function.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

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