Optic Disc and Retinal Strain Due to Vertical Duction

Purpose: To compare two-dimensional optic disc and retinal vessel strains due to vertical versus horizontal eye rotations in younger and older subjects using confocal scanning laser ophthalmoscopy (cSLO). Methods: In a younger subject group (n = 10; range, 18-39 years; mean age ± SD, 30 ± 6 years) and an older subject group (n = 29; at least 40 years of age; mean age ± SD, 67 ± 10 years), high-resolution infrared cSLO images were acquired in central gaze, 10° supraduction and infraduction, and 30° abduction and adduction. Images were segmented using a deep-learning model to identify retinal vessels, optic disc, and fovea. Ocular torsion was corrected, and eccentric gaze images were registered to the central gaze image. Displacement fields between image pairs were estimated using Recurrent All-Pairs Field Transforms (RAFT) optical flow and converted to two-dimensional strains. Repeatability was assessed on nine additional subjects (five younger, three older, and one child 14 years old) by analyzing duplicate image acquisitions. Results: Equivalent strain within the optic disc reached ∼2% during all four eccentric gazes despite smaller vertical ductions and decreased rapidly with distance from the disc. Younger subjects exhibited approximately twice the vessel strain as older subjects for the same gaze angles. Horizontal strain reached about 1% during adduction and was greater in eyes with longer axial length. Shear strain reached about 0.48% during supraduction. Conclusions: Modest vertical ductions produce two-dimensional retinal vascular strains comparable to large horizontal ductions. Age and axial length significantly influence strain magnitude during duction, suggesting that resulting mechanical loading on the posterior eye might be more significant than previously appreciated.