Abstract
Purpose :
Although optic nerve (ON) tethering occurs beyond ~26° adduction, the distribution of resulting ocular strain is predicted to vary depending on local tissue properties. We measured peripapillary strain by imaging displacements of embedded vessels using SLO during horizontal duction.
Methods :
Using azimuth rotation of Heidelberg Spectalis SLO to achieve 35° ab- & adduction from central gaze, we imaged a 8.9X8.9 mm2 region centered on the optic disc of young (42 eyes, age 27±5 years, ±SD) and older (39 eyes, 65±9 years) healthy adults. A MATLAB algorithm equalized brightness, corrected torsion, & registered globally across gaze positions. The VLFeat Team scale-invariant feature transform detector was used to quantify displacements of corresponding features that were analyzed in nasal vs. temporal sectors at disc radius increments from the disc center. A vessel mask was used to exclude non-vascular corresponding features from analysis.
Results :
Vascular features on the disc were displaced temporally in adduction & nasally in abduction. During adduction, nasal hemi-disc vessels were displaced temporally by similar amount of 11.0±23.0 μm in younger & 10.6±16.7 μm in older subjects. This was significantly more than the temporal hemi-disc was displaced nasally at 4.1±14.0 μm in young & 4.7±11.6 μm in older subjects (P=0.005). During adduction, nasally directed displacement of peripapillary vessels located >3 disc radii from center averaged 3.1±13.5 μm for younger, but only 0.5±12.2 μm for older subjects (P=0.02). Peripapillary features located between 2 & 3 disc radii shifted nasally in abduction by 2.4±13.3 μm in older (P<0.001) but not significantly in young adults at 0.0±8.8 μm. There were no significant vertical displacements in either group.
Conclusions :
Consistent with ON tethering, SLO demonstrates greater local disc & peripapillary vessel displacements in add- than abduction that are greater in the nasal than temporal hemi-disc. Since vessels are embedded in other tissues, these displacements represent local strains that are quantitatively similar in both younger & older subjects. Lesser peripapillary strain in older subjects during adduction may be due to scleral stiffening, which would increase associated stress during tethering. Lesser deformation in abduction than adduction is consistent with ON tethering in adduction but not abduction.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.