Lamina Cribrosa Microarchitecture in Monkey Early Experimental Glaucoma: Global Change

Abstract

PURPOSE. The purpose of this study was to characterize experimental glaucoma (EG) versus control eye differences in lamina cribrosa (LC), beam diameter (BD), pore diameter (PD), connective tissue volume fraction (CTVF), connective tissue volume (CTV), and LC volume (LV) in monkey early EG. METHODS. Optic nerve heads (ONHs) of 14 unilateral EG and 6 bilateral normal (BN) monkeys underwent three-dimensional reconstruction and LC beam segmentation. Each beam and pore voxel was assigned a diameter based on the largest sphere that contained it before transformation to a common cylinder with inner, middle, and outer layers. Full-thickness and layer averages for BD, PD, CTVF, CTV, and LV were calculated for each ONH. Beam diameter and PD distributions for each ONH were fit to a gamma distribution and summarized by scale and shape parameters. Experimental glaucoma and depth effects were assessed for each parameter by linear mixed-effects (LME) modeling. Animal-specific EG versus control eye differences that exceeded the maximum intereye difference among the six BN animals were considered significant. RESULTS. Overall EG eye mean PD was 12.8% larger (28.2 6 5.6 vs. 25.0 6 3.3 lm), CTV was 26.5% larger (100.06 6 47.98 vs. 79.12 6 28.35 3 10 6 lm 3 ), and LV was 40% larger (229.29 6 98.19 vs. 163.63 6 39.87 3 10 6 lm 3 ) than control eyes (P 0.05, LME). Experimental glaucoma effects were significantly different by layer for PD (P ¼ 0.0097) and CTVF (P < 0.0001). Pore diameter expanded consistently across all PDs. Experimental glaucoma eyespecific parameter change was variable in magnitude and direction. CONCLUSIONS. Pore diameter, CTV, and LV increase in monkey early EG; however, EG eyespecific change is variable and includes both increases and decreases in BD and CTVF