Can lamina cribrosa pressure challenge predict future structural glaucoma progression?

Abstract

Purpose : The lamina cribrosa (LC) has been hypothesized to be an initial target for glaucomatous damage. This study examines if changes in LC microstructure observed in OCT imaging under acute IOP modulation can predict future glaucomatous structural progression.

Methods : Subjects with glaucoma or glaucoma suspects underwent acute IOP modulation with an ophthalmodynamometer. IOP was increased to mild (30mmHg) and high (40-50mmHg) pressure settings while acquiring swept source OCT 3D cube images with orthogonal horizontal and vertical raster scans centered on the optic nerve head (ONH) and focused on the LC. Beam thickness-to-pore diameter ratio (BPR) and connective tissue volume fraction (CTVF; beam volume/total volume) were measured using an automated segmentation algorithm of our own design. Subjects with ≥3 follow up clinical visits where OCT scans of the ONH and macula regions were obtained (Cirrus HD-OCT; Zeiss, Dublin, CA) were enrolled. Subject’s retinal nerve fiber layer (RNFL) and ganglion cell inner plexiform layer (GCIPL) thicknesses rates of progression were computed by linear regression. A linear regression model adjusting for initial age and RNFL or GCIPL thickness was used to determine the association between LC microstructure changes and future rate of RNFL and GCIPL progression.

Results : Twenty eyes were included in the study (Table). A statistically significant and negative association was detected between change in BPR and CTVF from baseline to high IOP settings and the rate of GCIPL progression (Figure). Difference in CTVF from baseline to mild setting was also significantly and negatively associated with the rate of GCIPL progression. Therefore, a faster future rate of GCIPL thinning is observed when BPR and CTVF at high IOP setting are higher than baseline. No significant associations were detected with RNFL thickness progression. However, 30% of all eyes had initial RNFL thickness near the minimal measurable level (≤69µm). Previous studies have shown that GCIPL changes can be observed below the RNFL threshold.

Conclusions : Changes in LC structure in response to IOP modulation can predict future structural glaucomatous thinning of the GCIPL. The lack of RNFL associations is likely due to high prevalence of advanced RNFL damage in our cohort where only minimal further damage can be detected. The clinical implications of this “stress test” to predict glaucoma trajectory merit further study.

This abstract was presented at the 2023 ARVO Imaging in the Eye Conference, held in New Orleans, LA, April 21-22, 2023.