Abstract
Purpose :
To measure the strain response to intraocular pressure (IOP) decrease produced in the lamina cribrosa (LC) after suture lysis surgery and analyze for the effects of glaucoma damage.
Methods :
Twenty-nine suture lysis procedures after trabeculectomy were performed on 27 eyes from 26 glaucoma patients, average age = 68 years, IOP decrease = 12mmHg, and mean deviation (MD) range = -0.17 to -29.2dB. iCare IOP and radial scans by optical coherence tomography (OCT) of the optic nerve head were captured before and 20 minutes after suture lysis (Midgett et al. 2019). Images were enhanced (Fig. 1) and the anterior LC border manually marked. Digital volume correlation (DVC) was applied to the OCT images to calculate the strain response. Compliance of the strain response (strain/ΔIOP) and retinal nerve fiber layer (RNFL) were averaged overall and in four LC quadrants (inferior, superior, nasal, temporal). Linear regression was used to analyze relationships between strain, compliance, IOP, RNFL, MD, and visual field index (VFI).
Results :
A larger IOP decrease produced larger tensile anterior-posterior strain (Ezz), maximum principal strain (Emax), and maximum shear strain (Γmax) (p<0.01). Anterior lamina depth (ALD) did not consistently increase or decrease with IOP decrease; 24% of eyes had posterior ALD change. Eyes with thinner RNFL had a more compliant Emax, Γmax, and torsional shear strain (Eθz) response to IOP change (p<0.04) (Fig. 2). A more compliant Emax, Eθz, and Erz response was found for eyes with worse MD (p<0.05), and a more compliant Eθz and Erz for lower VFI (p<0.05). Analyzing quadrant averages showed that the association between thinner RNFL and more compliant Emax and Γmax response occurred in the nasal quadrant and also in the inferior quadrant for Γmax (p<0.05).
Conclusions :
IOP decrease predicted tensile strain, but not ALD change direction. The LC of eyes with greater glaucoma damage (thinner RNFL, worse MD, and lower VFI), had a more compliant strain response. These findings may result from progressive LC remodeling with glaucoma damage into a more curved structure or may represent baseline LC biomechanics prone to damage.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.