Abstract
Purpose :
Prior work has shown that iORGs are sensitive to the coherence length of the illumination source.1 However, these studies investigated this relationship in temporally separated trials, barring concurrent views of multiple coherence lengths in the same cell.2 This work assesses the impact of coherence length on iORGs when viewed both separately and simultaneously.
Methods :
Adaptive optics scanning light ophthalmoscopy was used to collect iORG data using three light sources centered at 850nm, 845nm, and 760nm with 1.6µm, 6.8µm, and 674µm coherence lengths, respectively. iORGs were acquired 1°-2° from the fovea in five individuals with no retinal pathology (1M, 4F; Ages=22-36 yrs) under five different illumination conditions (Table 1). Trials consisted of 10 videos collected after three minutes of dark adaptation. For stimulus trials, a 554nm (18.4µW) stimulus was presented for 68ms two seconds into each video. Prior to analysis, frames with mean pixel values below 35 were excluded. The remaining frames were standardized (µ=70; σ=35). Each cone was identified and iORGs were extracted and summarized using root mean square (RMS). We compared population-wide RMS amplitudes in the single-source illumination conditions using repeated measures ANOVA followed by Tukey’s multiple comparisons test. Single-cell RMS amplitudes were assessed in the two concurrent illumination conditions using the Wilcoxon signed-rank test.
Results :
The differences in population-wide RMS between the 1.6 µm and 674µm sources and the 6.8µm and 674µm sources were significant across all individuals (p<0.0002 for all but one: p=0.034). The difference between the 1.6µm and 6.8µm sources was significant in three individuals (p<0.05) and not significant in two (p=0.09 and 0.66). Significant differences were observed in concurrent illumination conditions (p<0.0001). Considerable variation was observed in concurrently measured iORGs, with substantial differences in amplitude and polarity in some cells and minimal differences in others.
Conclusions :
Illumination coherence length results in variable iORG differences across individual cells and participants. These data support the hypothesis that differences in coherence lead to changes in iORG waveforms, likely due to differences in the interference within cone outer segments.
1. PMID: 33379485
2. PMID: 19606274
This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.