Abstract
Purpose :
The single-flash light-evoked cone ORG is characterized by a fast contraction, followed by a slow elongation of cone outer segments (COS)(Pandiyan et al 2020, 2022). Prior work has hypothesized that the elongation is attributed to osmotic swelling resulting from an amplified byproduct of phototransduction. The paired-flash paradigm has been used extensively in ERG and patch-clamp electrical recordings to reveal mechanisms underlying sensitivity, kinetics and recovery of rod and cone photoresponses. Here, we characterize the recovery kinetics of the cone ORG using the same paradigm.
Methods :
Healthy subjects (n=3) were dark adapted for 2 minutes and imaged at 100 Hz volume rate using a coarse-scale ORG system (CoORG) based on a line-scan OCT (Jiang et al. 2022). The 3x3°imaging field was centered at 4° eccentricity. In each recording, an initial “test” stimulus (λ: 532±5nm, photon density: 6.9e6 photons/µm2, ~22% bleach) was presented followed by an identical second “probe” stimulus at various inter-stimulus intervals (ISIs) ranging from 0.5 to 40 s. COS length changes were extracted for the test and probe flashes using published methods for ORG processing. The recovery of probe flash amplitude and initial rate-of-rise were extracted and fitted with rising exponential functions of time (ISI) to quantify recovery kinetics.
Results :
The test flash cone ORG response followed prior reports. In contrast, the probe flash response showed substantially reduced amplitude and initial rate-of-rise of COS length at shorter ISIs, and then recovered exponentially to baseline as ISI increased. The recovery of the probe flash response to 1s ISI was particularly dramatic, exhibiting only 1/3rd and 1/10th of the rate and amplitude of the test flash response respectively. The maximum amplitude of the ORG response to the probe flash recovered to its baseline with a time constant of 9.4 ± 1.3 s while the initial rate-of-rise recovered three fold faster, with a time constant of 2.9 ± 0.3 s. These characteristics were consistent and repeatable among subjects.
Conclusions :
The recovery of the ORG response is consistent with the hypothesis of osmotically induced COS swelling and provides new insight into the properties of the amplified, osmotically active byproduct of phototransduction.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.