Abstract
Purpose :
Local displacements in and around the optic disc during horizontal duction have been demonstrated using scanning laser ophthalmoscope (SLO). Here, we used deep learning-based optical flow to map strains during horizontal duction in healthy adults over and under age 40 yrs.
Methods :
A Heidelberg Spectralis SLO with rotating azimuth camera head imaged fundus in central gaze, and 35° ad- and abduction for 22 younger (26±5 yrs, mean±SEM) and 19 older (64±10 yrs) adults. Image sets for central gaze paired with adduction, and central gaze paired with abduction were registered to minimize rigid body motion within pairs. The recurrent all-pairs field transformation (RAFT) optical flow was applied to image pairs to track feature points and precisely estimate displacements. To track feature points limited to retinal vessels that served as fiducials, vascular masks were generated using a convolutional neural network. Displacements were converted into strains.
Results :
In younger groups, tensile horizontal strain in the nasal hemidisc was significantly higher at 0.70±0.20% during adduction, while strain during abduction was nearly zero (P=0.014). There was little strain in the temporal hemidisc for either duction. In older groups, the greatest tensile horizontal strain was in the nasal hemidisc at 0.82±0.18% in adduction, which was insignificantly higher than tensile strain in abduction of 0.31±0.13%. In the temporal hemidisc of older groups, there was 0.52±0.21% compressive strain in adduction, but 0.28±0.25% tensile strain in abduction (P=0.001). During adduction, horizontal strain peripheral to the disc occurred only in the nasal peripapillary region as tension, and it decreased monotonically from disc to the most far periphery by an average of 21% and 35% in the younger and older groups, respectively. Vertical and shear strains were minimal for both duction directions in all areas.
Conclusions :
Adduction but not abduction creates tensile horizontal strains in the nasal half of the optic disc and nasal peripapillary retina of both younger and older adults. In the temporal hemidisc, older but not younger adults experience compressive horizontal strain in adduction and tensile strain in abduction. This may reflect optic nerve tethering in ad- but not abduction. Strain was less widely transmitted to the peripapillary region in older than younger adults, presumably due to tissue stiffening with age.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.