Abstract
Purpose :
To measure the long-term strains of the lamina cribrosa (LC) after lowering of intraocular pressure (IOP) by suturelysis compared to acute strains.
Methods :
LC of 12 patients (aged 66±7 years) who had trabeculectomy had optical coherence tomography (OCT) images before and 20 minutes after suturelysis and at follow-up 1-4 years later (Fig. 1). We published use of digital volume correlation (DVC) to correlate before to after lysis OCT scans to estimate acute LC strains and anterior LC border displacement (ALD) in these eyes (Czerpak 2022). Here, DVC was applied between follow-up scans and after-lysis scans to estimate long-term LC strains and ALD, which include the effects of creep, IOP change over time, and tissue remodeling in response to IOP-lowering. Linear regression was used to analyze for relationships between long-term strains, ALD, and IOP.
Results :
Mean IOP before trabeculectomy, after-lysis, and at follow-up were 20±8, 12±7 and 10±4 mmHg (iCare tonometry). While mean ALD did not change significantly just after lysis (1.33μm Czerpak 2022), mean ALD at follow-up was 63μm anterior, despite minimal additional IOP lowering (Table 1). Follow-up anterior-posterior strain Ezz was 10 times larger than acute Ezz (12% vs 1.2%). Higher before-trabeculectomy IOP was associated with greater expansion circumferential strain Eθθ (p=0.04). At follow-up, more anterior ALD was associated with greater tensile strain Ezz (p=0.007) and greater maximum principal strain, Emax (p=0.005). Thinner nerve fiber (RNFL) thickness was associated with larger long-term Ezz (p=0.03) and Emax (p=0.04). Eyes with a greater negative after-lysis shear compliance (after-lysis Ezθ /IOP decrease from lysis) had a greater long-term Ezθ (p=0.004).
Conclusions :
The immediate effects of IOP lowering are smaller than those measured years later. Remodeling increased LC thickness, reduced LC diameter, and increased anterior border movement. Long-term LC strains were greater with more RNFL loss. Progressive change in LC strains represent a new potential biomarker.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.