Dual-wavelength AOSLO imaging in the 13-lined ground squirrel

Abstract

Purpose : To develop a dual-wavelength AOSLO system for the 13-lined ground squirrel (13-LGS) that allows simultaneous collection of confocal and non-confocal signals generated by near-infrared (NIR) and visible (VIS) wavelengths.

Methods : A custom AOSLO was used to collect images of the cone mosaic in 4 (2M, 2F) 13-LGS during the late summer/fall-transition season. Simultaneous imaging with a long-coherence 785nm source (NIR) and a 673nm source (VIS) was done. The NIR confocal (NIRCON) signal was collected with a 40µm pinhole (1.67 ADD). Non-confocal light passing through an annular aperture (inner/outer diameter = 2.1 / 20.9 ADD) was halved and sent to two detectors in a “split-detection” scheme.^a The VIS confocal (VISCON) signal was collected through a 50µm annular aperture (1.63 ADD), and reflected non-confocal light was captured by an orthogonally-oriented quadrant detection scheme (inner/outer diameter = 5.2 / 18.7 ADD).^b 24 videos of 150-200 frames were collected, and 50-75 frames were registered and averaged to generate NIR and VIS confocal and non-confocal images. Split-detection images were calculated using multiple detector combinations: NIR left & right; VIS left & right quadrants; NIR left & VIS right; VIS left & NIR right; VIS top & bottom; and VIS diagonal quadrants.

Results : Variable reflectivity and multi-modal cones were observed in both NIRCON and VISCON images; combining the two images resulted in a more uniformly-appearing cone mosaic. Irregularly shaped sub-photoreceptor structures were observable in both NIR- and VIS- horizontal split-detection images, though additional morphological features were visible in VIS split-detection images. Relative to NIR split-detection images, image contrast appeared subjectively more uniform across VIS split-detection images; however there was no significant difference in relative cone contrast between the modalities (Wilcoxon signed rank test; p=0.83). In the mixed NIR-VIS split-detection images, we observed variation in the appearance of individual cones.

Conclusions : We demonstrated simultaneous dual-wavelength confocal and non-confocal AOSLO imaging in the 13-LGS. Similar contrast of the split-detection images between wavelengths is consistent with previous reports in human confocal images.^c Combinations of wavelengths and orientations may facilitate generating images that are more amenable to automated cone detection algorithms.

^aPMID: 24906859
^bPMID: 33680539
^cPMID: 16396019

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.