Purpose
To calculate and characterize the regional distributions of lamina cribrosa (LC) beam diameter (BD), pore diameter (PD), connective tissue volume (CTV) and connective tissue volume fraction (CTVF) from high-resolution, digital 3D optic nerve head (ONH) reconstructions of 23 normal NHP eyes so as to identify their correlations to LC thickness.
Methods
ONH reconstructions of 23 eyes (age 1.4 - 32.2 yrs) were aligned to a clinical photograph or confocal scanning laser tomographic (CSLT) image and the lamina cribrosa was 3D segmented [IEEE Trans Med Imag, 2006; 25:245-255]. Each voxel was assigned a “diameter” value based upon the largest sphere that fit inside the “beam” or “pore” in which it was contained. CTV was defined to be the total volume of beam voxels. CTVF was defined to be the ratio of CTV to total volume (pore + beam voxels). ONH, BD, PD, CTV and CTVF data were transformed into right eye orientation and mapped to a cylinder of radius 1.5 mm and 120 µm thickness. Data were regionalized into 12 sectors using the BMO centroid to foveal (FoBMO) axis as the horizontal midline allowing direct comparisons between eyes with varying laminar and scleral geometries. Mean BD and PD within each sector were normalized by dividing them by the standard deviation to ensure homogeneity of the residuals and hence validity of the subsequent analysis. Mixed effects models were constructed to detect effects of LC thickness accounting for spatially correlated data within each eye.
Results
BD (Mean / SD), CTV and CTVF were all significantly predicted by LC thickness; p=0.005 for BD, p<0.001 for CTV, and p=0.043 for CTVF. No relation was found between LC thickness and PD, p=0.149.
Conclusions
These data expand our previous characterizations of normal NHP LMA [H. Lockwood et al, ARVO, 2012; Roberts, et al IOVS. 2009;50:681-690] to include laminar BD, PD, CTV and CTVF to a total of 23 normal eyes. The regional distributions of normal NHP laminar BD, PD, CTV and CTVF are eye-specific, however pooled overall data for all 23 eyes (see plots below) suggest that BD and CTVF are correlated to LC thickness.
Keywords: 551 imaging/image analysis: non-clinical •
577 lamina cribrosa •
629 optic nerve