Abstract
Purpose :
It is well established which band in OCT images corresponds to the photoreceptor layer, yet no in vivo experiments support it. Our goal is to demonstrate which retinal layer in OCT images contains visual photopigments through correlation with two-photon vision psychophysics experiments.
Methods :
Two-photon (2P) vision is triggered when light from a pulsed light source is focused on the photopigments. SS-OCT device operating at 1.6MHz rate was used to trigger 2P vision and perform OCT imaging. 1.06μm wavelength light was seen by the subjects as green. OCT data were acquired in the fovea and 7° nasally from the fovea over 5°×5°FOV. The focal plane was moved across the retina over ±312μm from the photoreceptor layer in 31 steps. 6 data sets were taken at each. The same defocus steps were implemented in a random order in the 2P psychophysics experiment. A 5° horizontal line was scanned over the retina. For each defocus the subjects were matching the brightness of a green LCD screen placed in the eye fixation path to the apparent brightness of the OCT line providing a relative measure of the 2P perception intensity. 186 trials were completed. 4 normal subjects were tested. The accommodation was blocked with Tropicamide. The study was approved by the Bioethics Committee of NCU and was adhering to the Declaration of Helsinki.
Results :
The effect of defocus on the OCT images was analyzed in C-scans by calculating speckle contrast. With increasing beam defocus from the selected retinal depth, the contrast was deteriorating. Maximum contrast was occurring at different retinal depths as the focal plane was moving across the retina. 2P vision deteriorated as the beam was defocused from the layer containing photopigments. The focal plane position at which the 2P vision was strongest correlates with the maximum contrast of the inner/outer photoreceptor segments junction (IS/OS).
Conclusions :
2P vision can be used to determine in which retinal layer in the OCT images the visual photopigments are located. We were able to determine that the strongest 2P perception correlates with the maximum contrast of the IS/OS layer, demonstrating in in vivo experiment that the light-sensitive band is indeed identified in OCT images as the photoreceptors layer.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.