Abstract
Purpose :
To characterize the rod intensity-based optoretinogram (iORG) and compare its signal morphology to cone iORGs.
Methods :
Two subjects with no known retinal pathology were imaged using an adaptive optics scanning laser ophthalmoscope. iORGs were obtained in one eye of each subject over four trials consisting of 10 acquisitions each from a single location 10-12° temporal from each subject’s anatomical fovea. Each trial was preceded by 30 minutes of dark adaptation. Individual acquisitions consisted of 2 seconds of imaging with a 760nm single-wavelength laser, delivery of a 66ms 3.6uW/° stimulus (λ=554nm; Δλ=±45nm), and 5 seconds of post-stimulus imaging. The stimulus was designed to induce a ~4% rod bleach and ~7% cone bleach per delivery. Following data acquisition, each video was co-registered to ensure a cell-to-cell correspondence using custom software. Cone and rod locations were semi-automatically identified in the average image generated from all co-aligned videos. The iORG root mean square (RMS) signal was extracted from rods and cones using a previously described approach.1 Two measurements were extracted from each iORG RMS signal: amplitude, defined as the difference between the median pre and post stimulus reflectance, and intrinsic time, defined as the time to the maximum of the iORG RMS amplitude. Cone iORGs were compared to rod iORGs at the same location and assessed for differences in intrinsic time and amplitude.
Results :
We obtained iORGs from 970 cones and 959 rods. Cone intrinsic time was shorter than the rod intrinsic time for both subjects (506±166ms, 450±166ms vs 590±143ms, 602±121ms). Cone RMS amplitude was higher than the rod RMS amplitude (0.38±0.10, 0.38±0.08 vs 0.2±0.05, 0.16±0.06) for both subjects.
Conclusions :
We believe we have demonstrated the en-face intensity-based optoretinogram in rod photoreceptors for the first time. Compared to cone iORGs, rod iORGs exhibited a slower intrinsic time and lower amplitude, consistent with expected photopigment kinetics for these cell types. Further studies are needed to both assess individual rod iORGs and examine the rod iORG in individuals with retinal diseases that primarily affect rods.
1. PMC7771891
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.